PARAQUAT Supplement I: TOXICOLOGY

299 Pages·2016·2.3 MB·English

Australian Pesticides and Veterinary Medicines Authority

AUSTRALIAN PESTICIDES AND VETERINARY MEDICINES AUTHORITY

AUSTRALIA

CHEMICAL REVIEW PROGRAM

REVIEW OF THE MAMMALIAN TOXICOLOGY

AND

METABOLISM/TOXICOKINETICS

OF

PARAQUAT

Supplement I: TOXICOLOGY

Prepared by the

Agricultural and Veterinary Chemical Assessment Team
Office of Chemical Safety

of the

Department of Health

Canberra

October 2016

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PREFACE
This report was undertaken by the Office of Chemical Safety (OCS) at the request of the
Australian Pesticides and Veterinary Medicines Authority (APVMA), under the Chemical
Review Program. Paraquat is under review because of concerns over the potential risks to
human health and the environment.

A draft toxicology review was submitted to APVMA in 2003 and was subsequently revised
and updated in 2009, to address industry responses and to include additional published data. A
report focussing on neurotoxicity was requested of the OCS and submitted to the APVMA in
2010 with additional neurotoxicity studies assessed and incorporated in 2014.

In 2015, the complete review of the toxicology of paraquat was finalised and the report
structured into three parts:

• Summary Report
- Comprises an overview of all relevant data available on paraquat relating to human
health.

• Supplement I: Toxicology
- Comprises a detailed technical report on paraquat toxicology (excluding neurotoxicity)
[this report].

• Supplement II: Neurotoxicity
- Comprises a detailed technical report on paraquat neurotoxicity.

These three reports should be considered together. This report ‘Supplement I: Toxicology’, is
a complete evaluation of the data provided to the OCS, together with new information available
in the public domain since the commencement of the review, with the exception of
neurotoxicity.

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TABLE OF CONTENTS

1 ABBREVIATIONS ................................................................................................................ 5
2 EXECUTIVE SUMMARY ................................................................................................... 8
2.1 TOXICOLOGY HAZARD PROFILE ............................................................................................... 9
3 SUMMARY TOXICOLOGY REPORT............................................................................ 11
3.1 INTRODUCTION ....................................................................................................................... 11
3.2 METABOLISM AND TOXICOKINETICS ...................................................................................... 11
3.2.1 Oral Administration ............................................................................................................... 11
3.2.2 Inhalational Administration ................................................................................................... 12
3.2.3 Intrabronchial Administration ............................................................................................... 13
3.2.4 Ocular Administration ........................................................................................................... 13
3.2.5 Percutaneous Absorption....................................................................................................... 13
3.2.6 Human studies ....................................................................................................................... 14
3.2.7 In vitro Metabolism ............................................................................................................... 15
3.3 ACUTE STUDIES ...................................................................................................................... 15
3.4 SHORT-TERM STUDIES ............................................................................................................ 16
3.4.1 Oral administration ............................................................................................................... 16
3.4.2 Inhalational Administration ................................................................................................... 18
3.4.3 Dermal Administration .......................................................................................................... 18
3.4.4 Subcutaneous Administration ................................................................................................ 18
3.5 SUBCHRONIC STUDIES ............................................................................................................ 18
3.6 CHRONIC STUDIES .................................................................................................................. 19
3.7 REPRODUCTIVE STUDIES ........................................................................................................ 21
3.8 DEVELOPMENTAL STUDIES .................................................................................................... 23
3.9 GENOTOXICITY STUDIES ........................................................................................................ 25
3.10 NEUROTOXICITY STUDIES ...................................................................................................... 27
3.11 HUMAN STUDIES .................................................................................................................... 27
3.11.1 Occupational Exposure ......................................................................................................... 27
3.11.2 Poisoning Incidences ............................................................................................................. 29
3.12 MECHANISITIC STUDIES ......................................................................................................... 29
3.12.1 Antidote Studies ..................................................................................................................... 31
4 MAIN TOXICOLOGY REPORT ...................................................................................... 33
4.1 INTRODUCTION ....................................................................................................................... 33
4.2 TOXICOKINETICS AND METABOLISM ...................................................................................... 33
4.2.1 Metabolic Pathway ................................................................................................................ 33
4.2.2 Mice ....................................................................................................................................... 34
4.2.3 Rats ........................................................................................................................................ 36
4.2.4 Rabbits ................................................................................................................................... 44
4.2.5 Monkeys ................................................................................................................................. 47
4.2.6 Percutaneous absorption ....................................................................................................... 48
4.2.7 Human Poisonings ................................................................................................................. 55
4.2.8 In vitro Studies ....................................................................................................................... 60
4.3 ACUTE STUDIES ...................................................................................................................... 60
4.3.1 Acute Oral, Dermal and Inhalation Studies .......................................................................... 60
4.3.2 Eye and Skin Irritation and Skin Sensitisation Studies .......................................................... 65
4.4 SHORT-TERM REPEAT DOSE STUDIES ..................................................................................... 71
4.4.1 Oral Administration ............................................................................................................... 71
4.4.2 Inhalational Administration ................................................................................................... 99
4.4.3 Dermal Administration ........................................................................................................ 108
4.4.4 Subcutaneous Administration .............................................................................................. 115
4.5 SUBCHRONIC STUDIES .......................................................................................................... 118
4.5.1 Oral Administration ............................................................................................................. 118
4.6 CHRONIC STUDIES ................................................................................................................ 128
4.6.1 Mice ..................................................................................................................................... 128

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4.6.2 Rats ...................................................................................................................................... 138
4.6.3 Dogs ..................................................................................................................................... 153
4.7 REPRODUCTION STUDIES ...................................................................................................... 156
4.7.1 Rats (oral) ............................................................................................................................ 156
4.7.2 Mice (ip) .............................................................................................................................. 166
4.7.3 Rats (dermal) ....................................................................................................................... 168
4.8 DEVELOPMENTAL STUDIES .................................................................................................. 169
4.8.1 Mice ..................................................................................................................................... 169
4.8.2 Rats ...................................................................................................................................... 182
4.8.3 Rabbits ................................................................................................................................. 187
4.9 GENOTOXICITY STUDIES ...................................................................................................... 198
4.10 NEUROTOXICITY STUDIES .................................................................................................... 205
4.11 HUMAN STUDIES .................................................................................................................. 205
4.11.1 Occupational Exposure ....................................................................................................... 205
4.11.2 Poisoning Incidents ............................................................................................................. 216
4.12 MECHANISTIC STUDIES AND STUDIES ON TARGET ORGAN TOXICITY ..................................... 235
4.13 ANTIDOTE STUDIES .............................................................................................................. 259
5 REFERENCES .................................................................................................................. 270
5.1 EVALUATED STUDIES ........................................................................................................... 270
5.2 REFERENCES SEEN BUT NOT EVALUATED ............................................................................. 287
5.3 SECONDARY CITATIONS ........................................................................................................ 296

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1 ABBREVIATIONS

Time Weight
d Day bw Body weight
h Hour g Gram
min Minute kg Kilogram
mo Month mg Milligram
wk Week µg Microgram
s Second ng Nanogram
yr Year wt Weight

Length Dosing
cm Centimetre id Intradermal
m Metre im Intramuscular
μm Micrometre inh Inhalation
mm Millimetre ip Intraperitoneal
Nm Nanometre iv Intravenous
po Oral
sc Subcutaneous
mg/kg bw/d mg/kg body weight/day

Volume Concentration
L Litre M Molar
mL Millilitre ppb Parts per billion
µL Microlitre ppm Parts per million

Clinical chemistry
A/G Albumin/globulin ratio
ALT Alanine aminotransferase (SGPT)
ALP Alkaline phosphatase
AST Aspartate aminotransferase (SGOT)
BUN Blood urea nitrogen
CPK Creatine phosphatase (phosphokinase)
ESR Erythrocyte sedimentation rate
GGT Gamma-glutamyl transferase
Haematology
APTT Activated partial thromboplastin time
Hb Haemoglobin
Hct Haematocrit
LDH Lactate dehydrogenase
MCH Mean corpuscular haemoglobin
MCHC Mean corpuscular haemoglobin concentration
MCV Mean corpuscular volume
PCV Packed cell volume
PT Prothrombin time
RBC Red blood cell/erythrocyte

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WBC White blood cell/leucocyte
WBC-DC White blood cells – Differential count

Chemistry
ACTH Adrenocorticotrophic hormone
DMSO Dimethyl sulfoxide
DQ Diquat
eCG Equine chorionic gonadotrophin
EDTA Ethylenediaminetetraacetic acid
GC Gas chromatography
GLC Gas liquid chromatography
hCG Human chorionic gonadotrophin
HPLC High performance liquid chromatography
LSC Liquid scintillation counting
MPTP 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridine
MS Mass spectrometry
NAD(PH) Nicotinamide adenine dinucleotide (phosphate)
PQ Paraquat
TGAC Technical grade active constituent
TLC Thin layer chromatography

Terminology
AUC Area under the curve
CI Confidence Interval
F Female
FEV Forced expiratory volume
FVC Forced Vital Capacity
GLP Good Laboratory Practice
K Michaelis constant (substrate concentration at 1/2 V )
m max
LC Median lethal concentration
50
LD Median lethal dose
50
LOEL Lowest Observed Effect Level
M Male
MLD Maximum lethal dose
MTD Maximum tolerated dose
NOEC No Observed Effect Concentration
NOEL No Observed Effect Level
QA Quality Assurance
SCE Sister chromatid exchange
SD Sprague-Dawley or Standard Deviation
SEM Standard error of the mean
SPF Specific pathogen free
UDS Unscheduled DNA synthesis
V Volume of distribution
d
V Maximum velocity
max
Organisations
APVMA Australian Pesticides and Veterinary Medicines Authority
EC European Commission

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FAO Food and Agriculture Organization (United Nations)
IARC International Agency for Research on Cancer
MAFF Ministry of Agriculture, Forestry and Fisheries (Japan)
OCS Office of Chemical Safety
OECD Organization for Economic Co-operation and Development
PIC Poison Information Centre
US EPA United States Environmental Protection Agency
WHO World Health Organization

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2 EXECUTIVE SUMMARY

Paraquat is a non-selective contact herbicide belonging to the bipyridinium class of compounds
which also includes the herbicide diquat. Both compounds share a similar phytotoxic mode of
action which involves the inhibition of photosynthesis (specifically photosystem I) thereby
generating superoxide free radicals, leading to lipid peroxidation and membrane damage.
Plants die rapidly after treatment and subsequent exposure to light.

The main findings of the toxicology assessment are that the mechanism of mammalian toxicity
of paraquat, like its mode of action in plants, is via the generation of highly reactive free
radicals and consequent peroxidation of membrane lipids, sulfhydryl groups, proteins, and
DNA, leading to membrane damage and cell death.

The review confirmed the high acute toxicity of paraquat. The acute toxicity profile
demonstrates that in laboratory animals, paraquat is of moderate to high acute oral toxicity and
high acute inhalational toxicity, but low dermal toxicity. Paraquat is a severe eye irritant,
moderate skin irritant, but not a skin sensitiser. Paraquat is moderately to highly acutely toxic
to humans by the oral route. The review also confirmed that the repeat-dose toxicity of
paraquat, when administered by the oral or inhalational routes, is predominantly characterised
by pulmonary lesions due to the preferential uptake of paraquat by the lungs, with other effects
seen in kidneys and liver also noted following acute exposures.

From repeat dose studies there was no evidence to indicate that paraquat is carcinogenic in
chronic animal studies. The weight-of-evidence indicates that paraquat is non-mutagenic and
therefore is not considered to pose a genotoxic hazard to humans. Standard studies showed no
reproductive or developmental toxicity in experimental animals. The neurotoxicity potential of
paraquat is considered in detail in a separate report – Paraquat Toxicology Review Supplement
II – Neurotoxicity. The weight of evidence is that paraquat is not neurotoxic by the oral route
of exposure.

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2.1 Toxicology Hazard Profile

Absorption, distribution, metabolism and excretion in mammals
Poor; in the rat, approximately 10-18% of an orally
Rate and extent of absorption
administered dose is absorbed.
Dermal absorption Low; 0.3% in humans
Distributes to most organs of the body. The highest
Distribution
initial concentrations were found in the kidney and the
lungs.
No evidence of accumulation, other than potential
Potential for accumulation
accumulation in the lungs
Rapid; in the rat 60-90 % in faeces with 10-20% in urine
Rate and extent of excretion
in 72 h,
Not metabolised by rats. Generation of free radicals due
Metabolism
to redox-cycling, primarily in the lung, causing oxidative
tissue damage.
Toxicologically significant compounds
Paraquat and 2,2’:6’,2”-terpyridine (an impurity)
(animals, plants and environment)

Acute toxicity (Manufacturing concentrate; approx 34% w/w paraquat cation)
Note: Unless otherwise indicated, units are expressed as paraquat cation
Rat oral LD (mg/kg bw) 100-249
50
Worst oral LD in other species (mg/kg
50 22 (guinea pigs)
bw)
Lethal human dose (mg/kg bw)† 50 -80
Rat dermal LD (mg/kg bw) >1448 (no deaths)
50
Worst dermal LD in other species
50 No data
(mg/kg bw)
Rat inhalation LC (mg/m3) 0.5
50
Worst inhalation LC in other species No data
50
Skin irritation Moderate irritant (rabbit)

Eye irritation Severe irritant (rabbit)
Skin sensitisation
Non-sensitiser (Buehler method)
(No evidence of sensitisation in humans)

Acute toxicity of 2, 2’:6’, 2”-terpyridine (impurity)
Rat oral LD (mg/kg bw) 2.17 - 2.61
50
Rat dermal LD (mg/kg bw) 4.31 - 5.04
50

Short-term toxicity
Target/critical effect
Lungs/oxidative tissue damage
Lowest relevant oral NOEL
0.5 (13-week dietary study in dogs)
(mg/kg bw/d)
Lowest relevant dermal NOEL
Not established – no reliable studies
(mg/kg bw/d)
Lowest relevant inhalation NOEC
0.01 (21-day rat whole body exposure)
(mg/m3)

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Clastogenic effects at cytotoxic concentrations due to
Genotoxicity free radical damage.
Negative in vivo. Some in vitro equivocal results.
LOEL (mg/kg bw, single dose applied 6 (induction of micronuclei at this dose and higher in rat
dermally) bone marrow micronucleus assay)

Long-term toxicity and carcinogenicity
Target/critical effect Lungs/oxidative tissue damage
Lowest relevant NOEL
0.45 (pulmonary lesions in male dogs, 1-year study)
(mg/kg bw/d)
Carcinogenicity No evidence of carcinogenicity

Reproductive toxicity
No effect on reproductive performance. Toxic effects on
Reproduction target/critical effect offspring only at maternotoxic doses (perivascular
inflammatory cell infiltration in the lungs of pups).
Lowest relevant reproductive NOEL
3.75 in pups (perivascular inflammatory cell infiltration
(mg/kg bw/d, 3-Generation dietary study in the lungs)
in rats) 1.25 for parental animals (focal alveolar histiocytosis)

Developmental toxicity
Minor effects (delayed skeletal development at
Developmental target/critical effect
maternotoxic doses)
1 - maternotoxicity (increased mortality, clinical signs
Lowest NOEL
and reduced body weight gain)
(mg/kg bw/d, oral gavage in rats)
1 – foetotoxicity (reduced mean foetal and litter

weights).
<1 – maternotoxicity (effects on food consumption and
Lowest NOEL body weight gain at all doses tested)
(mg/kg bw/d, oral gavage in rabbits) 1 - foetal toxicity (increased incidence of post
implantation losses and skeletal variations)

Neurotoxicity Not neurotoxic by the oral route
Delayed neurotoxicity No evidence of delayed neurotoxicity
Immunotoxicity No data available
† Dose level at which there are reports of human deaths (Pond, 1990)

Note: Unless otherwise indicated ‘paraquat’ refers specifically to the paraquat cation

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