OFFICE OF THE PRIME MINISTER’S CHIEF SCIENCE ADVISOR

Professor Sir Peter Gluckman, ONZ KNZM FRSNZ FMedSci FRS
Chief Science Advisor

Methamphetamine contamination in residential properties: Exposures, risk
levels, and interpretation of standards

Draft Report

6 April 2018

1  Background
Methamphetamine: therapeutic use to drug of abuse
Methamphetamine  belongs  to  a  class  of  drugs  cal ed  stimulants.  It  is  a  legal y  prescribed
medication in the United States for the treatment of attention deficit hyperactivity disorder
(ADHD), obesity, and narcolepsy. It affects the brain and central nervous system by increasing
the amount of dopamine, a chemical associated with pleasure and reward, in the brain.
Because of its stimulant and euphoria-inducing properties, methamphetamine is commonly
used as a recreational drug. It is usual y smoked from a glass pipe, but it also can be injected,
snorted or swal owed. In the short-term, users experience symptoms such as increased heart
rate, attention, and wakefulness, agitation, and decreased appetite. Longer-term use results in
a  constel ation  of  side  effects  involving  physical  (weight  loss,  cardiovascular  and  organ
damage),  mental  (anxiety  and  confusion,  psychosis),  and  behavioural  (a  tendency  towards
recklessness and violence) aspects [1].
Methamphetamine is highly addictive, so recreational use in most cases leads to continual
drug-seeking behaviour and drug abuse. Once addicted, abusers require repeated and ever-
increasing doses to achieve a ‘high’. To pay for their habit they often turn to crime to support
their habit. There is a significant criminal activity associated with importing or manufacturing
and sel ing the drug. These factors further perpetuate the problem in the community.
The methamphetamine problem in New Zealand
Methamphetamine  is  not  used  therapeutical y  in  New  Zealand;  it  is  classified  as  a  Class  A
control ed drug under the Misuse of Drugs Act 1975. Due to the severity of the potential health

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risks  posed  by  its  abuse,  and  the  immense  social  costs  and  downstream  burden  on  wider
society, particularly the health and law enforcement systems, it carries severe penalties for
possession,  supply,  and  manufacture.  Possession  of  as  little  as  5  grams  (a  tablespoon)  is
enough to warrant a conviction for ‘possession for the purpose of sale or supply’.
In New Zealand methamphetamine is commonly known as ‘P’, ‘meth’, and ‘ice’. It is obtained
either through smuggling into the country, or by being manufactured local y in clandestine
laboratories  (so-cal ed  ‘clan  labs’  or  meth  labs)  using  common  household  equipment  and
accessible chemical ingredients.
New  Zealand  drug  use  surveys  suggest  that  methamphetamine  use  and  availability  are
increasing, and that prices are declining [2]. Gangs and professional drug dealers appear to
have  growing  involvement  in  its  supply  [3].  Remarkably,  methamphetamine  appears  to  be
more easy to obtain than cannabis throughout the country [4].
While methamphetamine supply seems to be plentiful, the number of confirmed meth labs
detected has been decreasing in recent years. Seventy-four meth labs were identified in 2016,
of which 50 were rental properties and 4 were Housing New Zealand properties [5]. Preliminary
data  suggest  that  border  seizures  of  ephedrine,  the  main  precursor  used  for  cooking
methamphetamine in New Zealand,a have declined. This may reflect a preference for obtaining
ful y  synthesised  methamphetamine  from  overseas  rather  than  manufacturing  local y.
Nonetheless, smal -scale meth labs are stil  likely to be active throughout New Zealand. These
meth  labs  may  be  found  in  residential  dwel ings,  commercial  accommodation,  and  even
vehicles.
Trends in methamphetamine manufacturing
Traditional methamphetamine manufacturing methods involve a range of hazardous (caustic
and  corrosive)  chemicals  and  solvents.  When  heated  and  volatilised  during  a
methamphetamine ‘cook’, these highly toxic substances contaminate the immediate area and
can  spread  through  the  dwel ing.  Exposure  to  such  contaminants,  either  by  being  present
during the production process (and thus likely inhaling volatile toxins in the air), or by coming
in contact with contaminated surfaces, poses a significant health risk.
However,  fol owing  a  number  of  restrictions  on  the  sale  of  solvents  and  certain  precursor
chemicals,  production  methods  changed  in  New  Zealand.  Now  the  most  commonly  used
methods do not use solvents, and the reaction is mostly performed in contained vessels that
do not emit fumes. Therefore, the primary contaminant associated with both manufacture and
smoking is methamphetamine itself.

a Use of pseudoephedrine as a precursor has not been common in NZ since it was reclassified from a
class C to a class B2 control ed drug in 2011, meaning it can only be obtained via prescription.

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Detecting methamphetamine in houses
Negative perceptions around methamphetamine have extended from societal worries about
the drug culture itself, to the effects left behind by its participants, including traces of the drug
in houses where it has been smoked. Media coverage of gang involvement in supply, and
criminal behaviour and serious health harms fol owing severe methamphetamine abuse, has
likely  contributed  to  the  overall  perception  that  any  contact  with  methamphetamine  is
inherently dangerous.
Techniques developed for forensic analysis to identify clandestine meth labs have evolved to
a high level of sensitivity that can detect very low levels of the drug and its precursors on
surfaces, to aid in the investigation of il icit drug production activity. These techniques have
increasingly been used in New Zealand to detect methamphetamine in houses, regardless of
whether or not criminal manufacturing activity is suspected, and an industry of operators that
test  and  remediate  contaminated  dwel ings  has  flourished.  This  industry  is  currently
unregulated,  with  some  operators  not  adhering  to  appropriate  and  scientifically  sound
sampling and clean-up guidelines.
The  extensive  publicity  surrounding  methamphetamine  contamination,  fuel ed  by  industry
claims of the high health risks posed by living in dwel ings where residues of the drug can be
detected, has led to considerable alarm especial y amongst tenants, landlords, and potential
home buyers and property investors. Evidence of contamination is placed in Land Information
Memorandum (LIM) reports, which impacts on property values. Outrage over the possibility of
innocent  parties  being  put  at  risk  by  the  irresponsible  and  il egal  actions  of  others  is
compounded by a lack of knowledge about the effects of chronic low-level exposure, and an
assumption that the presence of any level of residue would have adverse health effects.
Misunderstandings of hazard, exposure and risk
Concerns around the methamphetamine contamination issue in New Zealand appear to be
particularly  large  compared  to  other  jurisdictions,  and  likely  stem  from  misunderstandings
about the concepts of hazard, exposure and risk.
The risk posed by a hazardous substance (that is, a source of potential harm) depends on how
toxic it is, and the level of an individual’s exposure and sensitivity to it (Figure 1). For exposure,
things to consider include the amount of a substance a person is exposed to, how they are
exposed (the route of exposure – for example through the skin, or inhaling or ingesting the
substance), and how long they are exposed.

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Exposure
(dose)
Hazard
(toxicity)
Sensitivity
Risk

Figure  1:  Risk  of  a  hazardous  substance  is  dependent  on  levels  of  both  environmental  exposure  and
individual sensitivity.
In  this  context,  two  interrelated  factors  have  been  mostly  absent  from  the  discourse  on
methamphetamine contamination. The first is the level of methamphetamine found in affected
dwel ings, which dictates how much exposure a person can have by living there and coming
in  contact  with  the  affected  surfaces.  There  is  widespread  misperception  that  the  mere
presence of methamphetamine in a dwel ing, no matter how low the level, presents a health
risk  and  should  be  cleaned  up.  However,  general y  speaking,  the  mere  presence  of
methamphetamine does not present a health risk; it only poses a risk if there is a realistic route
and duration of exposure, and the doses are high enough throughout this exposure to have a
physiological effect.
The second factor is whether the dwel ing had been used for methamphetamine manufacture
(which may also involve smoking) or for smoking alone. This distinction is about what hazards
may be present. Dwel ings used for manufacture, depending on the process used, may pose
risks from a number of hazardous chemicals and by-products of production of the drug. In
contrast, with smoking the potential hazard is methamphetamine itself, residues of which may
be deposited on surfaces near where the activity occurred. The risk wil  be based on whether
the levels are high enough to result in physiological effects (and what those effects are) in
individuals exposed to them through skin contact or ingestion via hand-to-mouth transfer
from contaminated surfaces. These  issues are expanded upon in sections 2, 3 and 4.
New Zealand guidelines and standards
Because  of  the  known  risks  of  exposure  to  traditional  methamphetamine  manufacturing
chemicals and solvents, guidelines have been developed international y around cleaning of
contaminated  premises  after  a  meth  lab  has  been  discovered.  These  guidelines  use  the
detection of methamphetamine below a specified low level after remediation as a signal that
other contaminants have been sufficiently cleaned away.
In New Zealand, prior to June 2017, the threshold of residue levels at which a dwel ing was
considered to be ‘contaminated’ and thus require clean-up, was based on the 2010 Ministry
of Health Guidelines for the remediation of clandestine methamphetamine laboratory sites [6].
The guideline’s cut-off value was 0.5 µg of methamphetamine per 100 cm2 surface area, which

Mail: PO Box 108-117, Symonds Street, Auckland 1150, New Zealand
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was derived directly from an Australian assessment for meth labs [7], and is considered to be
very conservative – there is no evidence that chronic exposure to methamphetamine at levels
several times higher than this wil  lead to adverse health effects. Nonetheless, this guideline
provided a benchmark that was then used by the methamphetamine testing industry to signal
that  testing  and  remediation  was  necessary,  and  led  to  the  belief  that  even  low  levels  of
methamphetamine were potential y dangerous. It began to be used to test large numbers of
houses  for  any  traces  of  methamphetamine.  Despite  the  clean-up  guidelines  applying
specifical y to former meth labs, these types of properties became conflated with properties
unlikely to have been used for manufacture, leading to much confusion.
This threshold resulted in numerous properties testing positive for methamphetamine. The
efforts  of  Housing  New  Zealand  to  test  for  methamphetamine  and  remediate  properties
exceeding  the  guideline,  incurring  large  expenses  and  resulting  in  removal  of  numerous
properties available for habitation, have received intense media scrutiny. Emotive stories, such
as of tenants being evicted or of young families feeling unable to move into newly purchased
properties fol owing detection of methamphetamine residues, have also been reported. The
idea  that  residences  with  low  levels  presented  a  risk  that  needed  to  be  remediated  have
aroused fears and may have led to reporting of health affects believed to be attributed to
methamphetamine contamination.
A New Zealand Standard released in June 2017 [8] adopted a higher – but stil  conservative –
clean-up standard of 1.5 µg/100 cm2 without distinguishing between former meth labs and
non-meth  labs.  At  the  time  of  writing,  this  standard  has  not  yet  been  cited  in  an  Act  or
Regulation, and is therefore not yet legal y enforceable. The higher level of methamphetamine
allowable in the new standard has meant that a considerable number of properties that were
previously designated as needing remediation were now considered safe to occupy. However,
this does not mean that levels above the standard’s threshold are necessarily unsafe. In fact,
detecting levels above this should not be a cause for alarm, unless other factors suggest that
methamphetamine manufacturing activity has taken place within the dwel ing. This report aims
to explain this distinction more thoroughly.
2  Methamphetamine contamination: what’s the issue?
What does methamphetamine contamination really mean?
In this report, the term ‘contamination’ is used to refer to the presence of methamphetamine
as a non-natural substance. It is not intended to imply that levels are high, or, importantly, that
any health risk is posed.
In New Zealand, the term ‘methamphetamine contamination’ has been taken wel  beyond its
use in other countries. Where in other places the concern is primarily about what is left behind
after methamphetamine has been manufactured in a dwel ing, here the issue has been taken
more broadly to concern al  levels of detectable methamphetamine.

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How does contamination happen?
Methamphetamine residue can be deposited on surfaces within dwel ings in areas where the
drug has been ‘cooked’ or smoked. Some surfaces may be more contaminated than others,
depending on how close they were to the activity, and how frequently the activity was carried
out. Methamphetamine residues can be detected on surfaces only at trace levels by assays
that report levels general y in the range of 0.01–1,000 μg of methamphetamine per 100 cm2
surface area (ref 25, cited in [9]).
Is contamination different between meth labs and dwellings used for
smoking?
Manufacture  and  smoking  have  different  implications  for  health  risks,  because  while  both
result in surface contamination by methamphetamine, the former activity potential y involves
additional risks posed by residues of other hazardous chemicals used in the manufacturing
process. The specific range (and levels) of additional contaminants that may be present in the
dwel ing depends on the method of manufacture and rigour of the process [10], and toxicity
assessments on these contaminants have been made [7].
It is important to note that in New Zealand, methamphetamine has long been manufactured
mostly  using  smal ,  purpose  built  metal  cylinders,  and  involving  solvent-free  methods  [9].
Various chemical reactions that occur during manufacture are contained within this sealed
pressure vessel, which, unlike traditional glassware setups, prevents the release of associated
fumes and contaminants. This method of manufacture only releases methamphetamine and
very  smal   amounts  of  various  by-products  during  the  later  phases  of  the  manufacturing
process [9].
Nevertheless,  manufacture  in  general  results  in  greater  contamination  levels  for
methamphetamine  than  smoking  alone  [11].  Experiments  involving  simulated  smoking  of
methamphetamine found that contamination levels decline markedly over a few days [9, 12].
Samples taken soon after ‘smoking’ estimate that a single session may result in levels lower
than  0.1  μg/100  cm2,  and  multiple  sessions,  1.5–5.1  μg/100  cm2  [11].  These  levels  were
calculated using conservative measurements, and are likely to overestimate levels arising in
practice.
Methamphetamine levels that are observed in known former meth labs are substantial y higher
than  these.  Forensic  work  by  the  Institute  for  Environmental  Science  and  Research  (ESR)
suggests that levels of methamphetamine can be assessed against an ‘excessive’ threshold
that is indicative of manufacturing activity [9]. A US study has reported levels typical y higher
than 25 μg/100 cm2 [13], and New Zealand ESR data from 136 meth labs found an average
level of 54 μg/100 cm2, with about 25% of samples exceeding 30 μg/100 cm2 [9].b The ESR
data suggests that in a 20 m2 room, a level of 30 μg/100 cm2 would require around 1,500

b Further New Zealand data are available from ref [14] which reports levels from 20 suspected clan labs,
although interpretation is limited by most sites having been cleaned prior to sampling.

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smoke sessions. Hence, levels around or exceeding 30 µg/100 cm2 are regarded as strongly
suggestive of manufacturing activity.
What does this difference mean for health risks?
Although it is not possible to conclusively determine whether a dwel ing had been used for
manufacture or only for smoking based solely from the methamphetamine levels found, it is
reasonably straightforward to determine the health risks involved. Assuming that the same
level of methamphetamine residue has been found in two different dwel ings – one used only
for  manufacture,  and  the  other  only  for  smoking  –  then  the  health  risk  posed  by
methamphetamine itself is the same in both dwel ings.
In theory, a former meth lab may potential y have other contaminants that contribute to the
health risk. In cases where there are signs of traditional manufacturing activity, these may be
of concern if high levels of methamphetamine contamination indicate that cleaning has not
done.  However,  the  manufacturing  methods  most  often  used  in  New Zealand  now  mostly
involve sealed vessels that minimise contaminant spread, and use of highly toxic substances
such as lead and mercury has not been recorded [9]. In addition, since methamphetamine
levels are considered a marker for the levels of other potential contaminants, a former meth
lab containing low levels of methamphetamine is also likely to contain low levels of other
associated substances.
Hence  from  a  health  risk  perspective,  if  methamphetamine  levels  are  low,  it  is  likely  to  be
immaterial whether a dwelling was used as a meth lab or not. The relevance of distinguishing
between the two types of dwel ings relates to forensic and law enforcement purposes.
3  Establishing health-based standards for
methamphetamine exposure
A health-based risk assessment is a process used to estimate the nature and probability of
adverse health effects in people who may be exposed to chemicals in the environment. Such
assessments start with a toxicological characterisation of the substance to establish whether it
has the potential to cause harm (is it a hazard?), and if so, under what circumstances. This
involves determining the numerical relationship between exposure to the substance and any
resulting  health  effects,  known  as  a  dose-response  assessment.  After  this,  exposure
assessments are conducted to identify the extent to which the exposure actually occurs. Al  of
this information feeds into a risk characterisation, which forms a conclusion about the nature
and the size of the risk, and whether additional risk management measures are needed.
Toxicity assessments
We know that methamphetamine has the potential to cause harm (as do most chemicals if the
exposure is high enough) – but at what doses or exposures would this occur? The aim of a
toxicity assessment is to establish the relationship between an adverse effect of a substance

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(the harm it causes) and the dose (the exposure level) at which it takes place. Then, a threshold
‘dose’ can be calculated to indicate the dose that would have either no effect on human health,
or represent the lowest dose at which an effect might be observed. This difference in how the
threshold  dose  is  defined  is  important,  as  it  can  lead  to  very  different  thresholds  being
calculated.
Toxicity assessments on methamphetamine have been undertaken independently by the US
states of California [15] and Colorado [16, 17], for the purpose of establishing a risk-based
remediation standard for methamphetamine. California developed a ‘Reference Dose’ (RfD),
which is a formal toxicological measure that estimates the amount of a substance that humans
(including  children  and  other  sensitive  groups)  can  be  exposed  to  daily,  over  their  lifetime,
without  any  harmful  effects.  Because  there  are  no  data  to  suggest  that  low  doses  of
methamphetamine are toxic in humans, the assessment was based on a single clinical study
of methamphetamine used as a weight control therapy in pregnant women in order to have a
starting point from which to measure any dose effects [18]. The lowest dose that exhibited any
effect in this study was 5,000 μg per day (equivalent to 80 µg/kg body weight/day for the
average  woman).  Incorporating  a  large  safety  factor  to  ensure  that  there  would  be  no
possibility of an effect in even the most sensitive individual, the RfD was calculated to be 0.3
μg/kg body weight/day [15]. It means that an individual who may be especial y sensitive to
methamphetamine, such as a smal  child (10 kg) or a woman of childbearing age (70 kg), can
respectively consume 3 μg or 21 μg of methamphetamine every day for the rest of their lives,
without il  effect.
In contrast, Colorado developed a health-based reference value, which indicates the lowest
dose that humans (including children and other sensitive groups) can be exposed to at which the
first onset of any adverse health effect may occur. This value is distinct from a RfD, which by
definition is more conservative. The reference value was calculated, based on a number of
animal toxicology studies, as 5–70 μg/kg body weight/day (it is expressed as a range to
reflect the different results from the body of studies assessed) [16, 17]. Calculating from the
more  conservative  end  of  this  range,  the  lowest  dose  at  which  there  is  a  potential  for  an
adverse effect would be 55 µg of methamphetamine daily for a child, or 345 µg daily for an
adult.
A  comparison  of  the  two  assessments,  summarised  in  Table  1  and  further  described  in
Appendix 7.1, shows that the California-derived reference dose is more conservative than the
Colorado health-based reference value by a factor of between 17 and 233 (depending on
which end of the range – 5 or 70 µg/kg body weight/day – is taken). This means that Colorado’s
assessment allows for at least 17 times the amount of methamphetamine a sensitive individual
can be exposed to before possible onset of a health effect. This marked difference mainly
reflects the difference in how safety has been defined (i.e. level with no appreciable risk vs
lowest level at first possible adverse effect), and these definitions have in turn been informed
by very different types of studies (one primary human study vs multiple animal studies). It is
therefore not possible to give primacy to one assessment over the other, but it should be

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emphasised that both assessments incorporate very conservative assumptions and a very large
(~300-fold) safety factor.
Table 1: Summary of methamphetamine toxicity assessments

California (OEHHA)
Colorado (CDPHE)
Measure of toxicity
Reference dose
Health-based reference value
Definition
The  dose  at  or  below  which  Lowest dose at which an adverse
adverse health effects are unlikely  effect may occur
to occur
Study  population  and  Reduced  weight  gain  in  pregnant  Developmental and reproductive
effects
women
toxicity in laboratory animals
Calculated  dose  (μg/kg  0.3
5–70
body weight/day)

These values can also be placed in perspective by comparison with the recommended doses
for  therapeutic  purposes  (Figure  2).  Treatment  of  children  six  years  and  older  for  ADHD
symptoms begins at 5,000 µg and increases to about 20,000–25,000 µg daily, while treatment
of adults for obesity involves 5,000 µg per meal over a few weeks. As with most medications,
therapeutic use of methamphetamine may involve side effects such as headaches and appetite
loss, though it is not known how common these effects are [19].
20,000
20,000
15,000
15,000
10,000
5,000
5,000
se (µg/day)
6 26
100435
Do
0
California
Colorado
ADHD
ADHD
Obesity
therapy
therapy
(initial dose)
20-kg child
87-kg adult

Figure 2: Comparison of maximum daily intakes derived from the California and Colorado guidelines with
therapeutic daily doses for ADHD treatment in a six-year-old child or for obesity treatment in an adult.
The lower end of the recommended ADHD therapy dose (20,000 µg/day) for a six-year-old child is shown.
Obesity treatment dose assumes that three meals are consumed daily.
Estimating passive exposure doses to establish remediation guidelines
This section briefly describes how various jurisdictions have estimated the exposure doses of
sensitive individuals to methamphetamine in remediated dwel ings, and how these estimates

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were used to establish remediation guidelines. It is important to note that all the guidelines
(except  the  New  Zealand  ESR  report  [20],  as  discussed  later)  have  considered
methamphetamine residues only in former meth labs, and that residues arising from smoking
alone have not been considered.
Each  agency  used  different  mathematical  models  to  estimate  methamphetamine  exposure
doses. The models take numerous factors into account, such as the type of surface containing
the residue (hard floors or carpets), the way exposure to residues might occur (through skin
on  hands  and  body,  or  through  ingestion  from  a  child’s  ‘mouthing’  activity  with  toys  and
fingers), and how frequently the mouthing activity occurs. Where such data were not available,
best estimates from a conservative standpoint were used.
•  California found that, in order not to exceed their previously determined Reference
Dose  of  0.3  µg/kg  body  weight/day  for  a  child  aged  1–2  years  old,  the  surface
concentration of methamphetamine should be no higher than 1.5 µg/100 cm2 [21].c
•  Colorado analysed 3 proposed remediation standards: 0.05, 0.1, and 0.5 µg/100 cm2.
Their  model ing  found  that  for  an  infant,  a  6-year-old  child,  and  a  woman  of
childbearing age, a standard of 0.5 µg/100 cm2 led to exposure doses well below the
health-based reference value of 5,000–70,000 µg/kg body weight/day .d
•  In  Australia,  the  government  adopted  a  value  of  0.5  µg/100  cm2  as  a  clean-up
guideline [22] – this was based on a risk assessment report that model ed estimated
doses against California’s Reference Dose [7].e
New Zealand risk assessment
In 2010, the New Zealand Ministry of Health published a remediation guideline of 0.5 µg/100
cm2  for  former  meth  lab  dwel ings  [6].  This  was  directly  taken  from  the  Australian  risk
assessment report in lieu of a separate assessment.
A 2016 ESR report [20]f commissioned by the Ministry of Health has since proposed a New
Zealand-specific  set  of  remediation  standards.  It  estimated  the  total  exposure  doses  for  a
young child and for an adult woman (through whom a fetus may become exposed). It also

c The model also showed that the most important factor in determining overal  exposure dose was the
fraction of methamphetamine that is transferred from surface to skin.
d Remediation standards higher than 0.5 µg/100 cm2 were not assessed.
e This guideline is more conservative than that adopted by California, despite use of the same Reference
Dose. The risk assessment report attributed this to use of a less complex model to estimate exposure
doses, as wel  as use of more conservative estimates.
f This report provided an up-to-date review of the scientific and ‘grey’ literature on methamphetamine,
evaluated the remediation guidelines from other jurisdictions, and presented modelling work estimating
exposures for the New Zealand population. It differs from other assessments by providing guidelines
for both non-carpeted and carpeted dwel ings, and also distinguishing between dwel ings previously
used by methamphetamine smokers or by methamphetamine manufacturers.

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model ed the exposure doses in houses with and without carpets. In order not to exceed the
California Reference Dose, the following clean-up levels were recommended:
•  2 µg/100 cm2 for non-carpeted dwel ings that have not been used for manufacture.
•  1.5 μg/100 cm2 for carpeted houses not used for methamphetamine manufacture.
The level is lower because carpeted floors lead to higher exposure doses.g
Although in theory the above guidelines are appropriate for remediated houses regardless of
whether they had been used for manufacture or smoking, the report acknowledges that former
meth labs carry an additional risk of additional contaminants that may have been undetected
or not adequately removed during clean-up. Therefore, as a precautionary measure, the report
recommended the considerably more conservative guideline of 0.5 μg/100 cm2 for dwel ings
previously used for methamphetamine manufacture.
The rationale is that lower levels of methamphetamine are likely to indicate lower levels of
other chemicals. Thus, this lower level should not be interpreted as methamphetamine per se
posing a greater risk in a former meth lab. In theory, and according to the report’s guidelines,
a test result showing a level of 0.5–2.0 μg/100 cm2 in a known former meth lab would be
considered to pose no safety risk from methamphetamine itself.h
The New Zealand standard
In  June  2017,  Standards  New  Zealand  published  a  standard  on  the  testing  and
decontamination  of  methamphetamine-contaminated  properties  (NZS  8510:2017).i  The
standard does not focus on risk assessment or health effects, but the selection of a clean-up
level was informed by the 2016 ESR report. On the basis of this report and public submissions,
a single remediation level of 1.5 μg/100 cm2 was chosen, irrespective of whether the dwel ing
had been used for manufacture or smoking, or whether carpets are present or not.j
Table 2 summarises the chosen remediation values by each agency.

g California also include carpeting in their model, but only the single guideline of 1.5 µg/100 cm2 is
provided.
h  The  ESR  report  proposed  that  screening  for  lead  and  mercury,  which  are  heavy  metals  that  can
accumulate  in  the  body,  should  be  undertaken  in  dwel ings  formerly  used  as  clan  labs.  However  as
current manufacturing methods in New Zealand do not use these components [9], they are no longer
considered to pose a risk unless deemed otherwise by a forensic investigator (J Fowles, report co-author,
pers comm, 20 March 2018), or unless production methods change to include these components (C
Nokes, ESR, pers comm, 20 March 2018).
i  The  purpose  of  this  standard  was  to  provide  best  practice  guidelines  to  accurately  sample  and
effectively decontaminate affected dwel ings, and to ensure that methods for testing are reliable. The
wider aim was to ensure that a dwel ing previously used to manufacture or smoke methamphetamine
is safe for subsequent occupants.
j The reasons for adopting a single level, in contrast ESR’s four recommendations for specific situations,
are discussed in the Standards document [8]. They general y relate to practicability, for example that
not al  clan labs can be easily identified, and that sampling of carpet may itself be a destructive process.

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Table 2: Guidelines for maximum methamphetamine levels in remediated dwellings. Al  except for NZ
Standards are risk-based assessments. Note that Australia and ESR based their assessments on California’s
more conservative reference dose.

California  Colorado  Australia  NZ (ESR)
NZ
Standards
Former meth lab
1.5
0.5
0.5
0.5
Guideline
Carpeted  -
-
-
1.5
1.5  (3.8  for
(µg/100
Non-
low-use
2.0  (3.8*
cm2)
meth lab  Non-
areas)
-
-
-
for  adult
carpeted
woman)
* This value is higher than that for young children due to greater body weight and an assumed absence of
exposure via oral ingestion.
Comparison of the guidelines
Despite the variation in recommended remediation levels (Appendix 7.2), al  of the described
guidelines (except the New Zealand standards) are risk-based, meaning they take into account
the toxicity of methamphetamine as wel  as the potential levels of exposure to it.
There are two important points to be noted about al  of the remediation guidelines as a whole.
First, from a health perspective, none should be interpreted as a specific ‘threshold’ that if
exceeded – and particularly by a smal  margin – is likely to result in an adverse effect. The
second point is that all of the guidelines can be considered to be very conservative as they are
deliberately based on factors assuming ‘worst case’ scenarios that are unlikely to reflect a real-
world  situation  (Appendix  7.3).  It  should  also  be  noted  that  methamphetamine  does  not
accumulate in the body,k and animal studies suggest that the effects in the brain from single
or short-term exposure to a high dose are reversible [25].
Alternative calculations of risk levels
The ESR report calculated clean-up guidelines based on the level at which the California RfD
would not be exceeded. However, the ESR exposure data can also be scaled up to calculate
the  maximum  residue  level  at  which  Colorado’s  health-based  reference  value  wil   not  be
exceeded.l This calculation gives a maximum acceptable contamination level of 33 µg/100
cm2 for dwel ings without carpets, and 23 µg/100 cm2 for carpeted dwel ings.m These figures

k The time taken for half of an oral y ingested dose of 10–20 mg methamphetamine to be cleared from
the body (the ‘half-life’ – used in pharmacology to indicate how quickly a drug is eliminated) is about
10 hours [23], Within 24 hours, about 70% of the dose is excreted in urine [24].
l J Fowles, pers comm via C Nokes, 1 March 2018.
m ESR’s exposure data show that at a contamination level of 0.1 µg/100 cm2 in non-carpeted dwel ings,
the total exposure dose for a young child is 0.015 µg/kg body weight/day. This relationship was scaled
up in a linear manner such that a dose of 0.3 µg/kg body weight/day (i.e. California’s RfD) would be
reached  at  the  ESR  guideline  of  2  µg/100  cm2.  Further  extrapolation  to  a  dose  of  5  µg/kg  body
weight/day  (Colorado’s  health-based  reference  value)  results  in  a  value  of  33  µg/100  cm2.  The  ESR
analysis found that in a carpeted dwel ing a child would reach the California RfD at a contamination

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indicate levels above which an adverse health effect may be observed; in other words, lower
levels are unlikely to have health impacts. Notably, these figures are 15–22 times as high as
that adopted by Standards New Zealand.
A  similar  exercise  extrapolating  the  calculated  contamination  level  based  on  Colorado’s
exposure  data  and  their  own  health-based  reference  value  can  likewise  be  performed
(Appendix 7.4).
4  Are there health risks from passive methamphetamine
exposure?
The  health  risks  posed  by  methamphetamine  depend  primarily  on  the  type  and  level  of
exposure (Figure 3). The adverse effects of first-hand exposure – that is, its abuse involving
large doses over a prolonged period, are well documented. In New Zealand, the number of
hospitalisations attributed to methamphetamine abuse has risen dramatical y between 2012
and 2016, from 51 cases to 262 [5].
First-hand
Direct use
Dwel ing concurrently
used for manufacture
Second-hand
Dwel ing concurrently
used for smoking
Remediated
Dwel ing previously used
for manufacture
Non-remediated
Third-hand
Remediated
Dwel ing previously used
for smoking
Non-remediated

Figure 3: Methamphetamine exposure pathways. Note these are not mutual y exclusive.

level of 1.4 µg/100 cm2 (J Fowles, pers comm via C Nokes, 1 March 2018). Extrapolating this level in a
similar manner, using Colorado’s reference value, results in a value of 23 µg/100 cm2.

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There are also reports of il -health associated with second-hand exposure via residing in a
dwel ing concurrently or previously used as a clan lab [26, 27]. The drug can be detected in
hair of exposed children [28], in whom behavioural problems are common [26], although the
latter finding may be confounded by other social factors. Less is known about the effects of
breathing in smoke arising from methamphetamine use, and the US National Institute on Drug
Abuse notes that available evidence for negative health effects of second-hand exposure is
currently lacking [29].
In contrast, there are almost no known data relating to third-hand exposure situations, which
affect a greater majority of the population – that is, non-users living in dwel ings (whether
remediated or not) that had been  previously used only for smoking of methamphetamine
(Figure 3). To the best of our knowledge there is currently no available evidence in the scientific
or  grey  literature  that  low-level  methamphetamine  exposure,  involving  levels  that  may  be
encountered from skin contact or oral ingestion of residues on household surfaces, poses a
health risk in humans. Realistic scenarios of exposure through contact with surface residues,
even for toddlers who often put their hands in their mouths, do not suggest that levels would
reach close to a threshold where adverse effects would be observed.
Under the Health Act 1956, “poisoning arising from chemical contamination of environment”
is a notifiable disease [30]. This includes methamphetamine poisoning. Since 2013 a national
register  monitoring  diseases,  injuries  and  il nesses  from  hazardous  substances  has  been
maintained.n Between 2014 and 2016, two cases of food poisoning (from the same household)
were  attributed  to  methamphetamine  intake  via  a  contaminated  container [31].o  No  other
confirmed cases have been reported.
The Ministry of Health also notes that there have been no recorded cases in New Zealand of
poisoning  or  injury  arising  from  residing  in  dwel ings  that  had  been  previously  used  for
manufacture or use of methamphetamine.p While there have been some anecdotal reports of
minor il  effects associated with such dwel ings, as publicised in the media, there are no reports
on  whether  these  cases  have  received  a  formal  medical  diagnosis,  or  had  their  causes
attributed.  Furthermore, the  reported  symptoms (e.g.  asthma,  skin  rashes)  are  diverse  and
general y not known to be physiological effects of methamphetamine. The contribution of
other common factors known to affect health, such as dampness and mould, or other chemical
exposures in houses, has not been examined and may be equal y or more likely explanations
of the diverse symptoms claimed. Reporting of such effects to public health services appears

n  This  surveil ance  system  is  undertaken  by  Environmental  Health  Indicators  New  Zealand  (EHINZ),
Massey University, on behalf of the Ministry of Health.
o Additional details provided by D Read, EHINZ, pers comm, 4 April 2018.
p S Gilbert, Ministry of Health, pers comm, 21 Feb 2018. The Ministry has not received any notifications
of poisoning arising from chemical contamination of the environment under the Health Act 1956, or of
hazardous  substances  injuries  under  the  HSNO  Act  due  to  exposures  to  methamphetamine
contaminated dwel ings.

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to have declined fol owing the introduction of the new standard (NZS8510:2017),q with its
higher  ‘contamination  threshold’  for  a  property  requiring  cleaning.  This  suggests  that  a
significant proportion of the reports prior to this were based mainly on the perception that low
levels of methamphetamine were dangerous.
There  is  currently  very  limited  toxicity  data  that  can  inform  the  assessment  of  long-term
environmental exposures to methamphetamine residues. Methamphetamine is not considered
‘toxic’ at low doses – if it was, it could not be used as a therapeutic drug for ADHD and obesity.
It  is  not  listed  in  hazardous  substances  registries  such  as  the  ATSDR  (Agency  for  Toxic
Substances and Disease Registry), an extensive database run by the US Centers for Disease
Control and Prevention (CDC). However, some substances that are not toxic at low doses can
accumulate  in  the  body,  causing  adverse  effects  over  time.  Although  there  are  cumulative
effects  from  high-dose,  long-term  methamphetamine  use  due  to  its  addictive  effects,  the
chemical  itself  does  not  stay  in  the  body  or  accumulate  to  higher  levels.  Ingested
methamphetamine is general y eliminated from the body within about a day. This means that
doses  or  exposures  that  do  not  have  an  effect  in  the  short  term  are  not  additive,  and
theoretical y should not lead to any long-term harm.
Indeed, animal studies suggest that chronic low-doser methamphetamine promotes brain cell
development  and  function  [32],  and  improves  outcomes  fol owing  severe  traumatic  brain
injury [33, 34]. Clinical studies in humans with brain injury, involving multiple doses of 5,000–
100,000 µg D-amphetamine (a related drug with similar effects), have not reported any adverse
effects associated with the drug itself [35].
5  Towards an evidential and health risk-based approach for
managing potential exposure and contamination
Risk is a combination of the likelihood of a negative event happening (such as coming into
contact  with  a  level  of  methamphetamine  that would  produce  an  adverse  effect),  and  the
consequence of that event happening (what the effects are, and how serious they are). A risk-
based approach to methamphetamine contamination means that actions taken to manage the
potential health risks are proportionate to the level of risk.
Risks in perspective
When thinking about how to determine whether a risk is high enough to warrant substantial
mitigation measures, it sometimes helps to compare the risk to other similar risks, and consider
how they are dealt with (or not) in society. For example, we do not test for or regulate ‘third-

q D Barnfather and J Whitmore, Auckland Regional Public Health Service, pers comm, 21 March 2018.
r Rodents are less sensitive than humans to methamphetamine, and therefore higher absolute doses are
required to observe health effects. Thus the doses used in these studies are considered to be ‘low’ in
the context of animal research.

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hand  smoke’  residues  from  cigarettes,  which  contain  carcinogenic  polycyclic  aromatic
hydrocarbons  such  as  benzopyrene,  as  wel   as  nicotine,  which  are  measurable  on  indoor
surfaces  months  after  the  last  smoke  [36,  37].  Similarly,  other  household  hazards  such  as
mould, lead paint and asbestos pose greater health risks than third-hand methamphetamine
exposure (at least in a non-meth lab environment).
With regard to methamphetamine ‘contamination’, there is evidence in some New Zealand
communities that methamphetamine can be detected on banknotes [38, 39], and occasional y
at levels close to that found in many houses currently testing ‘positive’ and deemed to be in
need of remediation.
It is also worth noting that the UK Independent Scientific Committee on Drugs found in 2010
that the overal  harm caused by methamphetamine use is far outweighed by that caused by
alcohol [40].
Is the current approach in New Zealand commensurate with the risk?
What  we  know  from  the  preceding  discussion  is  that  the  likelihood  of  being  exposed  to
enough methamphetamine on household surfaces to absorb (through the skin or via hand-
to-mouth activities) a quantity that would have a physiological effect is extremely low, even in
young children. The effects of low-level exposure, if they occur, are likely to be transient – so
general y the consequences are also low. Considering the available evidence, the perception
of the risk, and the reaction to it in New Zealand, has been disproportionate.
New  Zealand  appears  to  be  unique  with  regard  to  its  approach  to  the  issue  of
methamphetamine  contamination  of  residential  properties.  While  other  countries  and
jurisdictions  have  also  established  standards  for  remediation  of  premises  where
methamphetamine clan labs have been identified, these standards are for the most part not
used for guiding clean-up of dwel ings where no manufacture has taken place. Some states in
the US issue only practical guidelines for cleaning a known (former) meth lab, and do not
require testing for methamphetamine levels [41].
The  international  guidelines  use  methamphetamine  as  a  marker  for  the presence  of  other
contaminants, recognising that these chemicals and solvents are the main hazards associated
with clandestine laboratories. The range and levels of contaminants vary widely among meth
labs, making it difficult and costly in practice to test for every single potential contaminant that
may  remain  after  clean-up.  It  is  for  this  reason  that  an  extra  conservative  guideline  is
specifical y for former clandestine labs, where lower levels of remaining methamphetamine are
assumed  to  indicate  lower  levels  of  other  contaminants.  This  does  not  imply  that
methamphetamine itself poses a greater health risk in former labs.
The trends in methamphetamine manufacturing in New Zealand mean that lab activity is no
longer always obvious in a dwel ing. But this also means that in general, production methods
are cleaner, and the main contaminant associated with any methamphetamine-related activity
is the drug itself. Nonetheless, the methamphetamine testing and decontamination industry

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has promoted the idea that al  properties are potential y in danger from methamphetamine
contamination.
A study by ESR of ~1,600 New Zealand public sector residential properties that were suspected
to  have  methamphetamine  contamination  can  provide  a  general  idea  of  the  range  of
methamphetamine levels that may be found in affected dwel ings [9]. Of the total number of
properties  tested,  approximately  two  thirds  showed  some  detectable  methamphetamine
‘contamination’. These dwel ings by definition represent a biased sample with higher potential
for  methamphetamine  contamination,  being  rental  accommodation  and  including  social
housing, and considering that in most cases the landlord or agency had ‘reasonable cause’ to
suspect methamphetamine use. The data are therefore likely to significantly overestimate the
extent of the problem in the wider New Zealand housing stock. The data show that out of
more than 13,000 surface samples taken, over 75% had methamphetamine levels under 1.5
μg/100 cm2, and approximately one third were negative. The average level in positive samples
was  2.7  μg/100  cm2.  Thus,  smoking-related  levels,  although  general y  exceeding  the  NZ
standard clean-up level, are stil  relatively low.
Less than 1% of the samples in the ESR dataset tested above 30 μg/100 cm2, suggesting a low
prevalence of properties potential y used for manufacture. Even then, toxic compounds such
as lead and mercury that are typically used in traditional production methods have not been
found in New Zealand.
Implications for methamphetamine screening in affected properties
Given the low probability of encountering excessive levels of methamphetamine in properties
where meth lab activity is not suspected, and also considering the very conservative nature of
the  standards  with  respect  to  the  risks  of  adverse  effects  from  third-hand  exposure  to
methamphetamine,  a  risk-based  approach  suggests  that  the  guideline  of  1.5  μg/100  cm2
should not be universal y applied.
Remediation is certainly warranted if high levels of methamphetamine are present that are
indicative of manufacturing activity or excessive smoking (levels >30 μg/100 cm2 signify that
manufacture is likely to have taken place; suggested testing criteria are lower [>15 µg/100 cm2
–  see  Recommendations).  Remediation  includes  removal  of  al   potential y  contaminated
porous materials or items (furnishings, carpets) and cleaning of the contaminated surfaces,
using the NZS 8510:2017 standard as a guide.
Where lower levels are detected, remediation is often not justified. However, as low levels
cannot definitively rule out manufacture, remediation down the 1.5 µg/100 cm2 standard may
be prudent if there is also sound reason to suspect previous clan lab activities. This would only
be  as  a  precautionary  measure  to  remove  other  toxicants  that  may  be  present  but  not
measured.
With regard to making screening of properties commensurate with the possible risks, some
specific aspects require consideration:

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Problems with field composite screening
Combining multiple samples taken throughout a dwel ing into a single composite sample, as
permitted in NZS 8510:2017, has limited value and does not accurately reflect levels of risk,
and depending on how the data are integrated can lead to quite misleading interpretation
and false impressions of high exposure. This approach of composite analysis is promoted as a
cost-effective option for initial screening, but it is in fact costly because it can falsely impose a
requirement for further testing without identifying the areas of potential contamination.
Given the low health risk in properties that were not used as meth labs, if they are to be tested,
the  initial  screening  should  not  involve  composite  field  testing  that  could  produce  a  false
positive result – that is, detecting a level of 1.5 μg/100 cm2  (or slightly above) from a composite
field  sample  that  adds  the  readings  from  al   swabs  together.  Such  field  composite  testing
means that every sample can be below the standard, but when combined can raise the overal
result, triggering another round of expensive testing.
Recommendations
•  Testing  for  methamphetamine  in  residential  properties  should  not  be  the  default
pathway. Testing is only recommended where meth lab activity is suspected or where
very heavy use is suspected.
•  Composite field testing that uses a cumulative value to make a yes/no decision against
the 1.5 μg/100 cm2  standard to determine ‘contamination’ should not be used.
•  There is merit in using tests that rapidly provide a simple positive or negative result in
multiple locations for detection of higher levels on site, fol owed by sensitive testing in
targeted  to  areas  that  produce  a  positive  signal.  For  example,  NIOSH-validated
colourimetric tests are available in the US that detect levels >15 μg/100 cm2 [42, 43].
In  most  cases,  if  methamphetamine  is  not  detected  at  this  level  anywhere  within  a
property, there is little cause for concern unless there are other reasons to suspect
methamphetamine  manufacturing  activity.  If  the  screening  test  shows  levels  >15
μg/100  cm2,  then  a  more  thorough assessment should  be  conducted  to  determine
whether there is an area of high contamination that needs to be remediated.
•  Where a former meth lab has been identified, remediation should continue to current
guidelines.
6  Conclusions
There is currently no evidence (in either humans or animals) that the levels typical y resulting
from third-hand exposure to smoking residues on household surfaces can elicit an adverse
health effect. Toxicity assessments and exposure dose models used to establish standards for
remediation  of  former  meth  labs  (and  which  are  used  in  the  NZS  8510:2017  to  guide
remediation  for  both  manufacture  and  use)  have  deliberately  adopted  very  conservative
assumptions, with very large (~300-fold) safety margins built in.

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Taken  together,  these  factors  indicate  that  methamphetamine  levels  that  exceed  the  NZS
8510:2017 clean-up standard of 1.5 µg/100 cm2 should not be regarded as signal ing a health
risk. Indeed, exposure to methamphetamine levels below 15 μg/100 cm2 would be unlikely to
give rise to any adverse effects.
Testing for low levels of methamphetamine in residential properties in New Zealand has come
at a very high cost. Although promoted as being protective of human health, the actions taken
in pursuit of zero risk have been largely disproportionate to the actual health risks. Trade-offs
need to be considered, particularly within social housing, where the risk of being in an unstable
housing situation is often greater than the risk of exposure to low levels of methamphetamine
residues. There have been huge costs to homeowners, landlords, and the state – not only of
testing and remediation itself, but the unnecessary stigma of ‘contamination’, often based on
little or no actual risk.
It is crucial that guidelines for mitigation measures are proportionate to the risk posed, and
that remediation strategies should be informed by a risk-based approach. This means that,
because  the  risk  of  encountering  methamphetamine  on  residential  surfaces  at  levels  that
might  cause  harm  is  extremely  low,  testing  is  not  warranted  in  most  cases.  Remediation
according to the NZS 8510:2017 standard is appropriate only for identified former meth labs
and  properties  where  excessive  methamphetamine  use,  as  indicated  by  high  levels  of
methamphetamine contamination, has been determined.
7  Appendix
7.1 Establishing threshold doses for methamphetamine
California: Reference Dose
To review the toxicity of methamphetamine, the California Environmental Protection Agency’s
Office of Environmental Health Hazard Assessment (OEHHA) relied primarily on human studies
[15].  From  the  available  literature,  a  study  on  pregnant  women  who  were  given
methamphetamine to control weight gain was used to calculate the RfD [18]. This is a 1961
placebo-control ed, double-blind study that involved relatively smal  sample sizes and did not
provide statistical analyses. However its findings were corroborated by another similar but
smal er  study  [44].  While  weight  change  does  not  necessarily  reflect  an  ‘adverse’  health
outcome, it gives an indication of dose levels at which physiological effects can be observed.
The  drug  was  given  in  a  sustained  release  formulation  (the  same  as  that  used  for  ADHD
therapy),  which  is  thought  to  best  mimic  the  continuous  exposure potential y  experienced
within a contaminated dwel ing.
Using the study data, the OEHHA determined that the lowest dose resulting in an observed
effect  on  weight  gain  was  5,000  µg/day  (equivalent  to  80  µg/kg  body  weight/day  for  the
average woman). Guided by other scientific literature on the effects of methamphetamine, the

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OEHHA  further  applied  widely  accepted  uncertainty  factors  to  this  value,  resulting  in  a
reference dose of 0.3 µg/kg body weight/day.
It is important to note that an RfD focuses on absence of potential for harm, and over the long
term. Thus, exceeding the dose even over an extended period is unlikely to result in an adverse
effect. Furthermore, this level is orders of magnitude lower than the doses that are prescribed
for therapeutic purposes (see Figure 2).
Colorado: Health-based reference value
The  Colorado  Department  of  Public  Health  and  Environment  (CDPHE)  reviewed  multiple
laboratory  animal  studies  on  the  developmental  and  reproductive  effects  of
methamphetamine exposure [16, 17]. They calculated that the dose at which 10% of the effect
can  be  observed  is  1,500–20,000  μg/kg  body  weight/day.  After  applying  conservative
uncertainty  factors,  a  health-based  reference  value  of  5–70  μg/kg  body  weight/day  was
determined. The lowest end of this range was derived from a single study showing decreased
fetal weight in mice [45]. This study intravenously administered 5,000 or 10,000 µg/kg body
weight/day methamphetamine to pregnant mice for 3–7 days. Decreased fetal weight was
observed in al  treatment groups. From this, the CDPHE calculated a benchmark dose level
(BMDL)s of 1,500 µg/kg body weight /day. Applying a safety factor of 300 yields a value of 5
µg/kg body weight/day.
Figure 4 compares the relative estimated doses for a typical young child and an adult woman
that would be reached at the California RfD and Colorado health-based reference value.

s  For this assessment, the BMDL was taken as the dose associated with the 95% confidence interval
around the BMD10 (the dose associated with a 10% effect).

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400
345
350
300
se (µg) 250
Do
200
150
100
55
50
21
3
0
California
Colorado
California
Colorado
Child
Adult

Figure 4: Maximum long-term daily dose of methamphetamine below which adverse events are unlikely
to occur (California), or above which an adverse health effect may occur (Colorado), for a 10-kg child and
a 70-kg woman.
7.2 Why are there so many different remediation guideline levels?
There are multiple reasons for the considerable variation in remediation guidelines among
different agencies.
•  Different mathematical models were used to estimate exposure doses: simpler models may
take fewer factors into account and involve more simplistic calculations; some may aim to
be especial y conservative while others provide better exposure estimations but with less
of a buffer. Further, the results of model ing can be only as rigorous as the quality of the
data being input, and each model relies on somewhat different assumptions from others.
•  There is a substantial difference between the California reference dose and the Colorado
health-based exposure value (0.3 vs 5–70 µg/kg body weight/day): this in turn directly
impacts on the calculated remediation level.
•  Unlike the other models, Colorado did not consider the contribution of carpet residues in
the exposure calculations. This is because guidelines developed specifical y for remediating
former clan lab dwel ings require that carpets be stripped, so it was assumed that carpeting
in  a  remediated  dwel ing  would  not  contain  any  residues.  Australia’s  ERS  did  find  that

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including soft surfaces led to a two-fold difference in exposure, but concluded that this
difference was “not considered to be sufficiently great” to warrant a separate guideline.
•  The ESR report distinguished between former meth labs and non-meth labs, while others
did not.
•  There  are  some  differences  in  interpreting  the  potential  for  methamphetamine  to
penetrate materials and re-surface over time.t
7.3 Conservative assumptions of exposure dose models
Toxicity assessments
•  The toxicity measures derived from California and Colorado’s assessments incorporate a
large  uncertainty  factor.  This  provides  a  safety  ‘buffer’  to  account  for  factors  such  as
differences in sensitivity among different people, uncertainties from extrapolating animal
data to humans, and uncertainties posed by incomplete toxicological information. Both
assessments used an uncertainty factor of 300. In other words, the values can be multiplied
by 300 to obtain the actual dose that was calculated to either not result in any adverse
effect, or result in the first sign of an effect.
•  Skin contact is the predominant route of exposure in  methamphetamine contaminated
dwel ings.  However  the  study  that  led  to  the  lowest  level  of  Colorado’s  health-based
reference  value  (5  μg/kg  body  weight/day)  involved  giving  pregnant  mice
methamphetamine  intravenously,  which  also  bypasses  oral  bioavailability  and  initial
metabolic breakdown, and so is likely to be highly conservative (see footnote v).
Exposure assessments
•  Estimates  of  exposure  levels  focused  on  the  most  sensitive  groups  such  as
crawling/mouthing young children, and adult women of childbearing age in whom a fetus
could potential y be exposed.
•  The models assumed that exposure levels remain constant after remediation, even though
simulated smoking experiments have found that even without intervention, levels of smoke
residues decrease significantly over just six days [9]. Other factors are likely to contribute
to further decreases over time, e.g. through cleaning, coming into contact with clothes and
being  laundered  out,  and  each  exposure  event  further  reducing  the  remaining  residue
levels.

t The NZ Ministry of Health [6] disagrees with California’s assumption that methamphetamine is volatile
(evaporates rapidly) and is not a persistent contaminant. It argues that residues may be absorbed in
building  materials  and  later  re-surface  and  evaporate,  leading  to  prolonged  exposure  and  at  levels
higher than indicated by surface testing alone. There is some evidence for this in the literature [46].
However, ESR considers these factors to be of minimal concern for several reasons. For example, the
contribution of airborne methamphetamine to overal  exposure is low, and over time young children
are likely to reduce their exposure though fewer mouthing behaviours, and reduce their effective dose
due to increasing body weight.

Mail: PO Box 108-117, Symonds Street, Auckland 1150, New Zealand
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Page 22 of 26

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•  Colorado’s model appears to be especial y conservative: it assumes that a child is clad in
just  a  nappy,  with  al   its  uncovered  skin  being  continuously  exposed  to  contaminated
surfaces for 12 hours a day.
•  For  methodological  reasons,  ESR’s  model  assumed  that  methamphetamine  was  100%
bioavailable through oral ingestion, but in practice bioavailability is thought to be 67%
[47]. This means that about one-third of the drug ingested is not actual y absorbed.
7.4 Contamination level at which Colorado’s health-based reference value
is reached
Colorado’s health-based reference value of 5–70 µg/kg body weight/day is at least 16-fold
higher than California’s Reference Dose of 0.3 µg/kg body weight/day. Because the Colorado
figure is much less conservative, it could be expected that their clean-up level would be much
higher than California’s guideline of 1.5 µg/100 cm2. Yet, their chosen guideline of 0.5 µg/100
cm2 is 3-fold lower.
This is because Colorado adopted a ‘health protective’ approach that simply assessed exposure
doses at a range of proposed clean-up levels (0.01, 0.1, and 0.5 µg/100 cm2), and whether any
of these levels would result in doses that exceed their health-based reference value. As none
of the proposed levels led to an exceedance, the highest level of 0.5 µg/100 cm2 was selected.
They did not assess even higher clean-up levels, or calculate the maximum clean-up level at
which the health-based reference value would be reached.
However there is expert opinion that such an approach is reasonable [48]. From the Colorado
exposure data, it can be calculated that the maximum surface concentration for not exceeding
the lowest level of their health-based reference value (5 µg/kg body weight/day) is 13 µg/100
cm2.u This means that levels exceeding 13 µg/100 cm2 may – but not necessarily – lead to
onset of an adverse effect.
As  previously  noted,  the  degree  of  conservatism  of  the  assumptions  used  in  models  of
exposure  can  have  a  large  impact  on  the  calculated  guideline.  This  can  be  il ustrated  by
recalculating  Colorado’s  exposure  data  using  two  modified  assumptions:  a  lower  oral
bioavailability (from 100% to 67%), and lower skin absorption (from 10% to 3%).v Using a lower
oral bioavailability alone, or lower skin absorption alone, resulted in a maximum level of about

u An infant is estimated to be exposed to 0.19 µg/kg body weight/day at a surface level of 0.5 µg/100
cm2.  Extrapolation  of  this  relationship,  which  has  been  determined  to  be  linear  [Kim16],  shows  that
exposure to 5 µg/kg body weight/day wil  result from a surface level of 13.1 µg/100 cm2.
v Because no data for skin absorption of methamphetamine were available, Colorado used 10% as a
default value recommended by the US Environmental Protection Agency. It has been suggested, based
on data from  a 1973 PhD  thesis studying the pharmacokinetics of methamphetamine,  that  the skin
absorption could reasonably be assumed to be 3% (L Schep, Dunedin School of Medicine, pers comm,
20 February 2018). California and ESR used a value of 57% based on data from an unpublished draft
report  (Hui  X  &  Maibach  HI  (2007)  In  vitro  percutaneous  absorption  of  d-methamphetamine
hydrochloride through human skin. Draft Report. Department of Dermatology, University of California,
San Francisco).

Mail: PO Box 108-117, Symonds Street, Auckland 1150, New Zealand
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Telephone: +64 9 923 6318   Email: [email address]    Website: www.pmcsa.org.nz

Page 23 of 26

15  µg/100  cm2;  combining  both  modified  variables  resulted  in  further  increase  of  the
maximum level to 25 µg/100 cm2.
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Mail: PO Box 108-117, Symonds Street, Auckland 1150, New Zealand
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