UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

Date: June 29, 2015 

SUBJECT: EDSP Weight of Evidence Conclusions on the Tier 1 Screening Assays for the 

List 1 Chemicals 

PC Code: See table, Attachment A 

Decision No.: NA 

Petition No.: NA 

Risk Assessment Type: NA 

TXR No.: See table, Attachment A 

MRIDNo.:NA 

DP Barcode: NA 

Registration No.: NA 

Regulatory Action: NA 

Case No.: NA 

CAS No.: NA 

40CFR: NA 

FROM: Greg Akerman & 

Health Effects Divison 

::~:E£'~:::e f]g:ams d f 'v--

Environmental Fat~~fec~~~n ~ Office of Pesticide Program 

THROUGH: Jess Rowland ~ S ~~~ Deputy Division Director 

Health Effects Division 

Office of Pesticide Programs 

TO: Jolene Trujillo 

Chemical Review Manager 

Pesticide Re-Evaluation Division 

Office of Pesticide Programs 

Ver.Apr. 2010 

EPA has completed its Weight of Evidence (WoE) assessment evaluating results of the 

Endocrine Screening Program (EDSP) Tier l screening assays for the List l chemicals. 

The WoE documents for the 52 chemicals are listed in Attachment A along with the chemical 

and report identifiers. 

Page I of2 

Page 1 of 56
Page 2 of 2 

Attachment A. EDSP List 1 Chemicals 

Chemical Name PC Code TXR Number 

2,4-D 030001 0057151 

Abamectin 122804 0057152 

Acephate 103301 0057153 

Acetone 044101 0057154 

Atrazine 080803 0057155 

Benfluralin 084301 0057156 

Bifenthrin 128825 0057157 

Captan 081301 0057158 

Carbaryl 056801 0057159 

Carbofuran 090601 0057160 

Chlorothalonil 081901 0057161 

Chlorpyrifos 059101 0057162 

Cyfluthrin 128831 0057163 

Cypermethrin 109702 0057164 

DCPA 078701 0057165 

Diazinon 057801 0057166 

Dichlobenil 027401 0057167 

Dimethoate 035001 0057168 

EPTC 041401 0057169 

Esfenvalerate 109303 0057170 

Ethoprop 041101 0057171 

Fenbutatin-Oxide 104601 0057172 

Flutolanil 128975 0057173 

Folpet 081601 0057174 

Glyphosate 417300 0057175 

Imidacloprid 129099 0057176 

Iprodione 109801 0057177 

Isophorone 847401 0057178 

Linuron 035506 0057179 

Malathion 057701 0057180 

Metalaxyl 113501 0057181 

Methomyl 090301 0057182 

Metolachlor 108801 0057183 

Metribuzin 101101 0057184 

MGK-264 057001 0057185 

Myclobutanil 128857 0057186 

Norflurazon 105801 0057150 

o-Phenylphenol 064103 0057146 

Oxamyl 103801 0057142 

PCNB 056502 0057138 

Permethrin 109701 0057149 

Phosmet 059201 0057145 

Piperonyl Butoxide 067501 0057141 

Pronamide 101701 0057137 

Propargite 097601 0057148 

Propiconazole 122101 0057144 

Pyriproxyfen 129032 0057140 

Simazine 080807 0057136 

Tebuconazole 128997 0057143 

Tetrachlorvinphos (TCVP) 083701 0057147 

Triadimefon 109901 0057139 

Trifluralin 036101 0057135 

Page 2 of 56
EDSP: WEIGHT OF EVIDENCE ANALYSIS OF POTENTIAL 

INTERACTION WITH THE ESTROGEN, ANDROGEN OR THYROID 

PATHWAYS 

CHEMICAL: OXAMYL 

OFFICE OF PESTICIDE PROGRAMS

OFFICE OF SCIENCE COORDINATION AND POLICY

U.S. ENVIRONMENTAL PROTECTION AGENCY

Page 3 of 56
OXAMYL FINAL 

ii 

TABLE OF CONTENTS 

Abbreviations...................................................................................................iii 

Executive Summary..........................................................................................1 

I. Introduction.......................................................................................3 

II. Sources of Scientific Data and Technical Information......................................4 

A. EDSP Tier 1 Screening Assays............................................................4 

B. Other Scientifically Relevant Information (OSRI)......................................4 

III. Weight of Evidence (WoE) Evaluation.......................................................4 

A. EDSP Tier 1 Screening Assays.............................................................7 

B. Effects on Hypothalamic-Pituitary-Gonadal (HPG) Axis..............................8 

1. Effects on Estrogen Pathway.....................................................8 

2. Effects on Androgen Pathway..................................................13 

C. Effects on Hypothalamic-Pituitary-Thyroidal (HPT) Axis...........................16 

IV. Committee’s Assessment of Weight of Evidence..........................................18 

A. Systemic/Overt Toxicity in the in vivo Tier 1 assays and OSRI .....................18 

1. Tier 1 in vivo Assays.............................................................18 

2. OSRI...............................................................................19 

B. Estrogen Pathway...........................................................................21 

C. Androgen Pathway.........................................................................21 

D. Thyroid Pathway...........................................................................21 

E. Conclusions.................................................................................22 

V. EDSP Tier 2 Testing Recommendations....................................................22 

VI. References.......................................................................................23 

LIST OF TABLES: 

 Table 1. Tier 1 Assays for Oxamyl....................................................................7 

 Table 2. Estrogenic/Anti-Estrogenic Pathway for Oxamyl .......................................10 

 Table 3. Androgenic/Anti-Androgenic Pathway for Oxamyl ....................................14 

 Table 4. Thyroid Pathway for Oxamyl ..............................................................17 

APPENDIX 1. EDSP Tier 1 Screening Assays..............................................................26 

APPENDIX 2. Other Scientifically Relevant Information (OSRI)....................................38 

APPENDIX 3. References Not Utilized in the Oxamyl WoE Analysis................................47 

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OXAMYL FINAL 

iii 

Abbreviations 

Abbreviation Terminology 

A Androgen (hormonal pathway) 

ADME Absorption, Distribution, Metabolism, Excretion 

ALP Alkaline Phosphatase 

ALT Alanine Aminotransferase 

AMA Amphibian Metamorphosis Assay 

ARTA Androgen Receptor Transcriptional Activation 

AST Aspartate Aminotransferase 

ANOVA Analysis of Variance 

AOP Adverse Outcome Pathway

AR Androgen Receptor

Bmax Binding at maximum

BROD Benzyloxyresorufin-O-dealkylase 

BUN Blood Urea Nitrogen

CAR Constitutive Androstane Receptor

CFR Code of Federal Regulations 

CG Cowper’s Gland 

ChE Cholinesterase 

ChEI Cholinesterase inhibition 

CMC Carboxymethyl cellulose 

CTA Comparative Thyroid Assay 

CV Coefficient of Variation 

CYP Cytochrome 450 

DER Data Evaluation Record

DMSO Dimethyl Sulfoxide

DNA Deoxyribonucleic Acid

DO Dissolved Oxygen

DP Dorsolateral Prostrate

E Estrogen hormonal pathway

EDSTAC Endocrine Disruptor Screening and Testing Advisory Committee 

EDRT Endocrine Disruptor Review Team

EDSP Endocrine Disruptor Screening Program

EE Ethinyl Estradiol

ELISA Enzyme Linked Immunosorbent Assay

EOGRTS Extended One-Generation Reproductive Toxicity Study (Rat)

ER Estrogen Receptor

EROD Ethoxyresorufin-O-dealkylase (or deethylase)

ERTA Estrogen Receptor Transcriptional Activation

EtOH Ethanol 

F Female 

F1 First filial generation 

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iv 

Abbreviation Terminology 

F2 Second filial generation 

Fcd Fecundity

FIFRA Federal Insecticide, Fungicide and Rodenticide Act 

FOB Field Observation Battery

FQPA Food Quality Protection Act

Frt Fertility

FSH Follicle Stimulating Hormone

FSTRA Fish Short-Term Reproduction Assay

FT Flutamide 

GD Gestation Day

GGT Gamma-glutamyl Transpeptidase

GnRH Gonadotropin-releasing hormone

GP Glans Penis 

GSI Gonado-Somatic Index

H High 

HLL Hind Limb Length

HPG Hypothalamic-Pituitary-Gonadal Axis

HPLC/MS/MS High Pressure Liquid Chromatography/Mass Spectroscopy

HPT Hypothalamic-Pituitary-Thyroidal Axis

I Inadequate 

IC50 Inhibitory Concentration at 50% of response

ICCVAM Interagency Coordinating Committee on the Validation of Alternative 

Kd Equilibrium Dissociation Constant 

KOW Octanol/Water Partition Coefficient 

L Low dose 

LABC Levator Ani-Bulbocavernosus

LAGDA Larval Amphibian Growth and Development Assay

LC50 Lethal Concentration in 50% of test organisms 

LD Lactation Day 

LH Luteinizing hormone 

LOAEC Lowest Observed Adverse Effect Concentration 

LOAEL Lowest Observed Adverse Effect Level 

LOQ Limit of Quantitation 

M Male 

MDL Minimum Detection Level

MEOGRT Medaka Extended One Generation Reproduction Test

MH Medium high 

ML Medium low 

MoA Mode of Action 

MOE Margin of Exposure

MRID Master Record Identifier 

MROD Methoxyresorufin-O-dealkylase 

MTC Maximum Tolerated Concentration 

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v 

Abbreviation Terminology 

MTD Maximum Tolerated Dose

N Negative 

NE Not examined/evaluated

NF stage Nieuwkoop and Faber’s Staging Atlas

NOAEC No Observed Adverse Effect Concentration

NOAEL No Observed Adverse Effect Level

NS Not Statistically Significant

NR Not Reported

OCSPP Office of Chemical Safety Pollution and Prevention

OECD Organization for Economic Co-Operation and Development 

OPP Office of Pesticide Programs 

ORD Office of Research and Development

OSCP Office of Science Coordination and Policy

OSRI Other Scientifically Relevant Information

P Positive 

P Parental generation

PC Positive Control 

PC10 Positive Control at 10% of response 

PC50 Positive Control at 50% of response 

PND Post-Natal Day

POD Point of Departure

PPS Preputial Separation 

PROD Pentaoxyresorufin-O-dealkylase (or depentylase)

PXR Pregnane X receptor

QC Quality Control 

RBA Relative Binding Affinity 

RBC Red Blood Cells 

RfD Reference Dose 

RPCmax Relative to Positive Control at maximum 

SAP Scientific Advisory Panel

SC Solvent Control 

s.c Subcutaneous 

SDH Sorbitol dehydrogenase

SDWA Safe Drinking Water Act 

SEP Standard Evaluation Procedure

SD Standard Deviation or Sprague-Dawley 

SVL Snout-to-Vent Length

SV Seminal Vesicles

T Thyroid (hormonal pathway)

T1WoERC EDSP Tier 1 Weight of Evidence Review Committee

T3 Triiodothyronine 

T4 Thyroxine (tetraiodothyronine) 

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OXAMYL FINAL 

vi 

Abbreviation Terminology 

TP Testosterone Propionate

TR Thyroid Receptor

TSH Thyroid Stimulating Hormone 

UDPGT Uridine Diphosphate Glucuronyltransferase (also known as UGT) 

VC Vehicle Control 

VO Vaginal Opening 

VP Ventral Prostate 

VTG Vitellogenin

WoE Weight-of-Evidence

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OXAMYL FINAL 

Page 1 of 48 

Executive Summary 

The Endocrine Disruptor Screening Programs (EDSP) Tier 1 assay battery is designed to 

provide the necessary empirical data to evaluate the potential of chemicals to interact with the 

estrogen (E), androgen (A) or thyroid (T) signaling pathways. This interaction includes agonism 

and antagonism at the estrogen and androgen receptors, altered steroidogenesis, as well as 

hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary thyroid (HPT) axes. In 

addition to the available Tier 1 assay data, other scientifically relevant information (OSRI), 

including general toxicity data and open literature studies of sufficient quality were considered 

in this weight of evidence (WoE) assessment. 

In determining whether oxamyl interacts with E, A or T hormone pathways, the number and type 

of effects induced, the magnitude and pattern of responses observed across studies, taxa and 

sexes were considered. Additionally, the conditions under which effects occur were considered, 

in particular, whether or not endocrine-related responses occurred at dose(s) that also resulted in 

general systemic toxicity or overt toxicity. 

On May 14, 2014, the EDSP Tier 1 Assay Weight of Evidence Review Committee (T1WoERC) 

of the Office of Pesticide Programs (OPP) and the Office of Science Coordination and Policy 

(OSCP) conducted a weight-of-evidence analysis of the potential interaction of oxamyl with the 

E, A or T hormone pathways. The T1WoERC conclusions from the WoE evaluation in this 

report are presented by pathway (E, A and then T) beginning with the results of the Tier 1 in 

vitro assays followed by in vivo mammalian and wildlife results, then the results of the cited 

OSRI for mammalian and wildlife studies (40 CFR Part 158 and literature). 

For oxamyl, there was no convincing evidence of interaction with the estrogen pathway. The 

Tier 1 in vitro assays were negative (ER binding, ERTA, aromatase, and steroidogenesis assays), 

as well as the Tier 1 uterotrophic assay. In the female pubertal assay, while there were increases 

in uterine weights; however, the absence of complimentary data does not support estrogenrelated etiology for this effect. No treatment-related effects observed in the FSTRA. 

For the androgen pathway, there was no convincing evidence of interaction. The Tier 1 in vitro

(i.e, AR binding and steroidogenesis) and Hershberger assays were negative. No androgenrelated effects were observed in the Tier 1 male pubertal assays or mammalian Part 158 studies. 

In the FSTRA assay, while there was an increase in GSI at high dose, no other effects were 

observed. 

There was no evidence of interaction of oxamyl with the thyroid pathway. Thyroid parameters 

were not altered in Tier 1 mammalian or amphibian in vivo studies, except for a non-dosedependent increase in thyroid weights in the female pubertal rat (20% and 13% at the mid and 

high dose, respectively). 

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Page 2 of 48 

Based on weight of evidence considerations, mammalian or wildlife Tier 2 testing is not 

recommended for oxamyl since there was no convincing evidence of potential interaction with 

the estrogen, androgen or thyroid pathways. 

 

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OXAMYL FINAL 

Page 3 of 48 

I. Introduction 

The Endocrine Disruptor Screening Programs (EDSP) Tier 1 assay battery is designed to 

provide the necessary empirical data to evaluate the potential of chemicals to interact with the 

estrogen (E), androgen (A) or thyroid (T) signaling pathways. This interaction includes agonism 

and antagonism at the estrogen and androgen receptors, altered steroidogenesis, as well as 

hypothalamic-pituitary-gonadal (HPG) and hypothalamic-pituitary thyroid (HPT) axes. In 

addition to the available Tier 1 assay data, other scientifically relevant information (OSRI), 

including general toxicity data and open literature studies of sufficient quality were considered 

in this weight of evidence (WoE) assessment. 

In determining whether oxamyl interacts with E, A, or T hormone pathways, the number and 

type of effects induced, the magnitude and pattern of responses observed across studies, taxa, 

and sexes were considered. Additionally, the conditions under which effects occur were 

considered, in particular, whether or not endocrine-related responses occurred at dose(s) that also 

resulted in general systemic toxicity or overt toxicity. 

On May 14, 2014, the EDSP Tier 1 Assay Weight of Evidence Review Committee (T1WoERC) 

of the Office of Pesticide Programs (OPP) and the Office of Science Coordination and Policy 

(OSCP) conducted a weight-of-evidence analysis of the potential interaction of oxamyl with the 

E, A or T hormone pathways. The T1WoERC conclusions from the WoE evaluation in this 

report are presented by pathway (E, A and then T) beginning with the results of the Tier 1 in 

vitro assays followed by in vivo mammalian and wildlife results, then the results of the cited 

OSRI for mammalian and wildlife studies (40 CFR Part 158 and literature). 

Oxamyl has a vapor pressure of 2.3 × 10-4 mm Hg at 20 to 25°C, and will exist as a vapor if 

released to the atmosphere. Oxamyl is soluble in water (280 g/L at 25°C); it has an octanol/water 

partition coefficient (log Kow) of -0.47. Oxamyl is susceptible to photolysis in the atmosphere, 

with a half-life of approximately 1.4 days. Volatilization from water is not expected to 

significantly contribute to the dissipation of oxamyl in the environment. The estimated 

bioconcentration factor is 3.1. 

The available information considered in determining the potential interaction of oxamyl with the 

E, A, or T pathways include submitted EDSP Tier 1 assays and/or other scientifically relevant 

information (OSRI) such as general toxicity studies and other published articles. These data are 

summarized in Sections III.A through III.C. An analysis of the data submitted to the agency, 

using the WoE approach outlined by the Agency (USEPA, 2011), is presented in Section IV. The 

EDSP Tier 2 study recommendations are presented in Section V. 

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II. Sources of Scientific Data and Technical Information 

A. EDSP Tier 1 Screening Assays 

The Tier 1 assays and/or other scientifically relevant information (OSRI) submitted to satisfy the 

agency’s test order are shown below in Table 1. Executive Summaries are presented in Appendix 

1. 

B. Other Scientifically Relevant Information (OSRI) 

In response to the Agency’s Test Orders, data believed to be relevant to one or more of the Tier 1 

assays were submitted as OSRI by the Test Order recipients and/or the public. This included 

studies published in the open literature and/or data submitted to support pesticide registration 

(e.g., Part 158 Guideline studies). The Agency’s review of the initial OSRI is provided in the 

Report of the Endocrine Disruptor Review Team on OPP (USEPA, 2010). Since then, the 

Agency has also conducted a more recent search of available scientific literature for any 

additional relevant information. Summaries of the available OSRI are presented in Appendix 2. 

Additionally, literature/studies considered but not utilized for the WoE analysis are listed in 

Appendix 3. 

III. Weight of Evidence (WoE) Evaluation 

The principles, criteria and approach used in the WoE determination on the potential of a 

substance to interact with endocrine-related processes (i.e., E, A, or T hormone pathways) were 

as described in the WoE guidance document (USEPA, 2011) and presented at the 2013 FIFRA 

Scientific Advisory Panel (SAP) (USEPA, 2013). The weight of evidence process identifies how 

the individual lines of evidence are assembled and integrated along two concepts (i.e., 

complementarity and redundancy) within the conceptual framework of an adverse outcome 

pathway). Broadly, there are four main steps outlined in the guidance which provide the 

foundation for WoE evaluations. The first step is to evaluate the individual studies for their 

scientific quality and relevance in evaluating potential endocrine interaction(s). The second step 

is to integrate the data along different levels of biological organization while examining the 

extent of complementarity (i.e., the concordance of endpoints within an assay that measures 

multiple endpoints) and redundancy (i.e., the concordance of endpoints/responses across assays) 

in the observed responses across these different levels of biological organization. The third step 

is to characterize the main lines of evidence as well any conclusions. Finally, the last step is to 

evaluate whether additional testing is needed based on the evidence and conclusions described 

above. 

As mentioned, the first step is to assemble and evaluate the available scientific data. Data for the 

EDSP Tier 1 WoE evaluation falls into one of two categories: 1) EDSP Tier 1 data, or 2) other 

scientifically relevant information (OSRI). The EDSP Tier 1 data includes a battery of 11 assays 

consisting of in vitro and mammalian and wildlife in vivo assays. The Tier 1 assays were 

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Page 5 of 48 

designed specifically to evaluate a number of key biological events including potential effects on 

receptor binding (estrogen and androgen agonist and antagonist), steroidogenesis, and other 

effects on the HPG and HPT axes. OSRI may include published literature studies as well as 

studies conducted under USEPA (often referred to as Part 158 data) or OECD guidelines 

submitted in support of pesticide registrations. Each study is evaluated for scientific quality and 

relevance for informing interactions with the E, A, or T pathway. Additionally, the consistency 

of the responses in the individual study is evaluated. For the Tier 1 in vivo assays, often multiple 

endpoints are measured in each assay. 

Evaluation of the potential confounding effects of overt toxicity in the study, as well as the 

relative degree of diagnostic utility of a specific endpoint for discerning whether or not the 

chemical has interacted with the endocrine system, are considered. The collective response of the 

individual endpoints, as well as the conditions under which they were expressed, are considered 

when evaluating an overall indication of potential interaction as measured by the study. 

The second step in this WoE process is to formulate hypotheses and integrate the available data 

along different levels of biological organization. Two keys elements in the integration of data, as 

well as characterizing the extent to which the available data support a hypothesis that a chemical 

has the potential to interact E, A, or T pathways, are the concepts of complementarity and 

redundancy. These two concepts provide a basis for considering the plausibility, coherence, 

strength, and consistency of the body of evidence. The current EDSP Tier 1 screening assays are 

meant to evaluate whether or not a chemical can interact with E, A, and T consisting of different 

levels of biological organization from a molecular initiating event such as receptor binding 

through potential adverse effects in apical endpoints such as sexual development and fecundity at 

the whole organism level. The extent of expression of responses at higher levels of biological 

organization can indirectly provide information on potential compensatory capabilities of an 

individual organism. 

After the data have been assembled and integrated, the third step is to characterize the main lines 

of evidence along with the conclusions; this characterization involves three components. The 

first component is whether the data provide relevant, robust and consistent evidence in terms of 

complementarity and redundancy as well as biological plausibility. Second, is at what level of 

biological organization were the responses observed and whether organisms exhibit 

compensatory responses at higher levels of biological organization? Finally, under what 

conditions where the responses occur including consideration of whether the responses were 

observed in the presence of overt or systemic toxicity? The presence of overt and/or systemic 

toxicity introduces uncertainty in the ability to distinguish effects specifically related to an 

endocrine-related effect from a non-endocrine toxic response. 

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This uncertainty in distinguishing whether the responses were endocrine-related was discussed at 

the FIFRA SAP meeting that evaluated scientific issues associated with the WoE evaluation of 

the EDSP Tier 1 screening process. In October 2013, the SAP stated that, “In summary, the 

Panel agreed that little, if any, weight should be placed on signs of endocrine disruption in the 

presence of overt toxicity. All effects in endocrine sensitive tissues should be evaluated in terms 

of primary interactions with the endocrine system vs. secondary effects related to toxicity in nonendocrine organs or overall disruptions in homeostasis” (USEPA, 2013). 

For these WoE analyses, overt toxicity was generally defined in accordance with EPA’s current 

approach as used by OPP in reviewing 40 CFR Part 158 studies for both human and ecological 

risk assessments. Specifically, in these analyses, the effects that EPA considered to be potential 

evidence of overt toxicity included, but were not limited to: mortality; clinical signs such as 

tremors, ataxia and abnormal swimming (fish and aquatic-phase amphibians); and body weight 

decreases of ≥10% in mammals. Additionally, other effects including morphological (e.g., organ 

weights/histopathology), biochemical (e.g., blood chemistry), and other clinical signs (e.g., 

lethargy) were also considered when evaluating overt toxicity, especially if the effects were 

extreme. In some instances, one parameter (i.e., death or >10% decrease in mammalian body 

weight) was sufficient to consider a dose/concentration to be overtly toxic. However, in other 

instances, more than one parameter was needed to determine overt toxicity. For example, in the 

FSTRA, generally, body weight decreases were considered along with other responses when 

assessing potential overt toxicity. Additionally, effects which were considered to be signs of 

systemic toxicity were also captured and these effects were generally considered as less severe 

forms of toxicity (e.g., changes in organ weights or blood chemistry). The circumstances for 

which a dose/concentration was considered overtly toxic for a particular study are described in 

Section IV.A. 

In summary, EPA considers multiple lines of evidence in including the observed responses in 

the Tier 1 assays and OSRI in the context of a chemical’s physical/chemical properties and its 

known modes of action in its overall characterization of a chemical’s potential to interact with 

the E, A or T pathway. Adequately addressing the three main components described above is 

fundamental to the WoE process and in determining whether additional data are needed. In 

addition to characterizing the WoE, reviewers also considered: 1) uncertainties and their 

potential impact to conclusions; 2) discussion of key studies; 3) description of inconsistent or 

conflicting data; 4) overall strength of evidence supporting a conclusion; and, 5) what, if any, 

additional data are needed and why. Assessing the need for additional data is based on a caseby-case analysis which took all available toxicity data into account. 

The WoE approach involved consideration of data (i.e., lines of evidence) from the EDSP Tier 1 

assays and OSRI which are depicted in Tables 2 - 4. These tables contain data that are 

considered scientifically and biologically relevant with regard to a treatment-related effect 

which supports a conclusion of whether a substance has the potential to interact with the E, A, 

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Page 7 of 48 

or T pathway. Effects that occurred in the presence of overt toxicity are discussed in the text for 

each respective pathway (E, A or T) but are not reported in the table for E, A or T. 

A. EDSP Tier 1 Screening Assays 

The Tier 1 assays submitted in response to the agency’s test order for oxamyl are shown below 

in Table 1. 

Table 1. Tier 1 Assays for Oxamyl

Tier 1 Assays Test Guideline Test Order Status 

ER Binding Assay 

(Rat uterine cytosol) OCSPP 890.1250 Requirement Satisfied (MRID No. 48672702) 

ERα Transcriptional Activation Assay

(Human cell line HeLa 9903) 

OCSPP 890.1300; 

OECD 455 

Requirement Satisfied 

(MRID No. 48686701) 

AR Binding Assay 

(Rat prostate cytosol) OCSPP 890.1150 Requirement Satisfied (MRID No. 48672703) 

Steroidogenesis Assay 

(Human cell line H295R) 

OCSPP 890.1550; 

OECD 456 

Requirement Satisfied 

(MRID No. 48686702) 

Aromatase Assay 

(Human recombinant microsomes) OCSPP 890.1200 Requirement Satisfied (MRID No. 48672701) 

Uterotrophic Assay (Rat) OCSPP 890.1600; 

OECD 440 

Requirement Satisfied 

(MRID No. 48618401) 

Hershberger Assay (Rat) OCSPP 890.1400; 

OECD 441 

Requirement Satisfied 

(MRID No. 48618402) 

Pubertal Female Assay (Rat) OCSPP 890.1450 Requirement Satisfied 

(MRID No. 48702104) 

Pubertal Male Assay (Rat) OCSPP 890.1500 Requirement Satisfied 

(MRID No. 48702103) 

Fish Short-term Reproduction Assay OCSPP 890.1350; 

OECD 229 

Requirement Satisfied 

(MRID No. 48702101) 

Amphibian Metamorphosis Assay 

(Frog) 

OCSPP 890.1100; 

OECD 231 

Requirement Satisfied 

(MRID No. 48702102) 

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Page 8 of 48 

B. Effects on Hypothalamic-Pituitary-Gonadal (HPG) Axis 

1. Effects on Estrogen Pathway 

The potential for oxamyl to interact with the estrogen pathway is summarized in Table 2. If an 

effect was observed but considered by WoE not to reflect a direct interaction, then the effect is 

discussed in the text but not presented in the table. The various targets of the estrogen pathway 

across the relevant Tier 1 assays are delineated so as to facilitate determination of potential for 

estrogenic, anti-estrogenic, or HPG axis effects. This table also includes HPG-relevant findings 

from data evaluated as OSRI. Effects that occurred in the presence of overt toxicity are discussed 

in the text but are not reported in the table and not considered further in the WOE assessment. 

Oxamyl was negative (or not interactive) in the Tier 1 in vitro ER binding, ERTA aromatase, and 

steroidogenesis assays. Oxamyl was also negative in the in vivo uterotrophic assay. In the 

female pubertal rat assay, the average age at attainment of VO was decreased by 1.8 days at the 

low dose, and by 1.7 days at the high dose. The average day of first estrus was increased 0.9 day 

(not statistically significant, NS). These changes in puberty attainment were not dose-dependent 

and not considered biologically significant. Compared to control, wet and blotted uterus weights 

were increased by 62 and 43% at the low dose and by 34 and 27–28% at the high dose. The 

overall changes in uterus weight were not dose-dependent, however when non-cycling animals 

are excluded from the analysis, the changes appear to be dose-dependent: wet uterus weight 

increased 59% and 54%, and blotted uterus weight increased 38% and 45% at the low and high 

dose. After adjusting for stage of estrus, the changes in the uterine weights also appear to be dose 

dependent1

: blotted weight ↑22.8% at the low dose and ↑34.0% at high dose for animals in the 

proliferative phase, and 22.7% at low dose and ↑27.1% at high dose for animals in the nonproliferative phase (concomitant increases in wet weight also appeared to be dose-dependent). 

No estrogen-related effects were observed in the mammalian Part 158 data. 

In the FSTRA, there were no treatment-related effects on fecundity, fertilization, GSI or plasma 

VTG concentrations. While there were no reported treatment-related effects on gonadal stages or 

histopathology, oocyte atresia and granulomatous inflammation was observed in both the 

controls and treatment groups with the inflammation associated with presence of spores 

 

1

 For each dose groups, necropsied animals were estimated to either be in a proliferative or non-proliferative stage of 

estrus based on the latest cyclicity determination and assuming 4 days per cycle. Animals determined not to be 

normally cycling were excluded from the analysis. The changes in proliferating animals were not statistically 

significant. Statistically analysis could not be performed in the non-proliferating animal groups because the control 

group had only one animal. 

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(presumed microsporidia). However, according to the report, it did not appear that the presence 

of either microsporidia or the inflammation had any effect on the study results. While effects on 

mortality or other clinical signs were not observed, female body weight was decreased 13% 

(p<0.05) in the high-dose group (0.989 mg a.i./L). 

In the Part 158 avian reproduction study with mallard ducks, mortality and observations of penmate aggression were observed in the control and all treatment groups. The study indicated a 

slight effect on egg production and a potentially higher chance of egg infertility at 50 mg/kg-diet. 

Due to increased mortality in the control (14%, all females), there is concern with the ability to 

discern endocrine-related effects seen in the mallard study due to the presence of mortality and 

aggressive behavior in the pens. In the Northern bobwhite quail study, there were no 

reproductive impairments observed up to 50 mg/kg-diet. Also, no treatment-related effects on 

mortalities, bodyweight or clinical signs of toxicity were observed in this study. In a Part 158 

freshwater fish early life-stage toxicity test with rainbow trout, at 1.5 mg/L (highest 

concentration tested), significant delays in the first day of embryo hatching and larval swim-up 

were observed, as well as a significant decrease (↓96%) in the percentage hatching.

Page 17 of 56
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Page 10 of 48 

Table 2. Estrogenic/Anti-Estrogenic Pathway for Oxamyl Lines of Evidence Indicating Potential Interaction with the Estrogenic/Anti-Estrogenic Pathway for Oxamyl1Study Type / Literature Citation 

ER Binding 

ER Activation 

Steroidogenesis 

Sex Steroid 

Hormone 

Uterine Weight 

Ovarian Weight / 

GSI 

Ovarian/Gonad 

Staging and 

Histopathology 

Pituitary Weight 

Estrous Cyclicity 

Age & Weight at 

VO 

2° Sex 

Characteristics 

Fertility (Frt) / 

Fecundity (Fcd) 

Vitellogenin (VTG) 

EDSP Tier 1 Assay 

ER Binding (MRID 48672702) N ERTA (MRID 48686701) N4 Steroidogenesis (MRID 48686702) NAromatase (MRID 48672701) N Uterotrophic (MRID 48618401) N Female Pubertal Rat (MRID 48702104) NE ↑ 27–34 (L, H)5 N N N N N FSTRA (MRID 48702101) NE N N N N N 

OSRI 

Developmental toxicity (Rat; MRID 40859201) NE N Developmental toxicity (Rabbit; MRID 00063009) 

N N 

Two-generation reproduction (Rat; MRID 41660801) 

 NE NE N NE N 
OXAMYL FIN

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Table 2. Estrogenic/Anti-Estrogenic Pathway for Oxamyl Lines of Evidence Indicating Potential Interaction with the Estrogenic/Anti-Estrogenic Pathway for Oxamyl1Study Type / Literature Citation 

ER Binding 

ER Activation 

Steroidogenesis 

Sex Steroid 

Hormone 

Uterine Weight 

Ovarian Weight / 

GSI 

Ovarian/Gonad 

Staging and 

Histopathology 

Pituitary Weight 

Estrous Cyclicity 

Age & Weight at 

VO 

2° Sex 

Characteristics 

Fertility (Frt) / 

Fecundity (Fcd) 

Vitellogenin (VTG) 

Chronic toxicity / carcinogenicity (Rat; MRID 41963101) 

NE N N NE

Carcinogenicity (Mouse; MRID 00076813) 

NE N N NE 

Chronic toxicity (Dog; MRIDs 41697901/42052701) 

NE NE N NE

Avian reproduction (Bobwhite Quail; MRID 00116610) 

 N 

1. Key to responses: L=Low treatment, ML=Medium-low treatment, M=Medium treatment, MH=Medium-high treatment, H=High 

Arrows (↓ or ↑) indicate the direction of the response. A shaded cell indicates that is parameter is not routinely evaluated or is not a

Changes in weight are absolute unless otherwise indicated. 

2. The systemic toxicity in the Tier 1 assays are presented in this column (e.g. KW= kidney weight). The systemic toxicity for the OS

this column. For details see Section IV. A 

3. The overt toxicity in the Tier 1 assays are presented in this column (e.g. ↓BW). The overt toxicity for the OSRI is indicated by an X 

details see Section IV. A 

4. Although the conditions of this assay were not optimal to detect very weak activity, oxamyl responses were similar to those of the 

corticosterone and not comparable to the responses of 17α-methyltestosterone (very weak positive control). Oxamyl was only able 2.9-4.4% PC when tested up to the highest concentration (10-5.3 M). Because the RPCMax < PC10 in both assay runs, oxamyl was co

estrogen receptor transcriptional activation in this test system. 

5. Mean uterus weight changes (not corrected for estrus stage or cycling status) were not dose-dependent. Wet weight increased 62% 

increased 43% at the low dose, while wet weight increased 34% and blotted weight increased 27–28% (absolute-relative) at the higcycling animals are considered in the analysis, changes are dose dependent (Blotted: 38% at low, 45% at high dose; p =0.0031 for 

for pairwise by Dunnett’s. Wet: 59% at low, 54% at high dose; p=0.0043 for trend, p<0.05 and p<0.01 pairwise for low and high danalyzed by estimated estrus stage (based on latest vaginal smear before termination and excluding non-cycling animals), changes dependent (statistics not available). 
OXAMYL FIN

Page 12 of 48 

6. While effects on mortality or other clinical signs were not observed, female body weight was decreased 13% (p<0.05) in the high-d

(0.989 mg a.i./L). 

P Positive findings N Negative findings (in vitro) / No effect (in vivo) 

NE Not examined 
OXAMYL FINAL 

Page 13 of 48 

2. Effects on Androgen Pathway 

The potential for oxamyl to interact with the androgen pathway is summarized in Table 3. If an 

effect was observed but considered by WoE not to reflect a direct interaction, then the effect is 

discussed in the text but not presented in the table. The various targets of the androgen pathway 

across the relevant Tier 1 assays are delineated so as to facilitate determination of potential for 

androgenic, anti-androgenic, or HPG axis effects. This table also includes HPG-relevant findings 

from data evaluated as OSRI. Effects that occurred in the presence of overt toxicity are discussed 

in the text but are not reported in the table and not considered further in the WOE assessment. 

Oxamyl was negative in the Tier 1 in vitro AR binding and steroidogenesis assays. The 

Hershberger assay was negative and no androgen-related effects were observed in the Tier 1 

male pubertal assay. 

In the FSTRA, there was an increase in male gonado-somatic index (GSI) of 30% in the highdose group (0.989 mg a.i./L), but no other effects (e.g., plasma VTG concentration, gonadal 

stages, and histopathology) were observed. There were no treatment-related effects on mortality, 

male body weight or clinical signs of toxicity. 

No androgen-related effects have been reported in oxamyl Part 158 mammalian toxicity studies, 

except in the two-generation reproductive study. In that study, increased average relative testes 

weights were observed (F0 high-dose, ↑19%; F1 medium and high-dose, ↑12 and 33%, 

respectively) and co-occurred with overt toxicity [(decreased average male body weight at the 

mid (↓7–20% F1) and high dose (↓10–18% F0, ↓17–37% F1)]. In the Part 158 northern bobwhite 

quail study, there were no androgen-related effects observed up to 50 mg/kg-diet; in the mallard 

duck study, potentially higher chance of egg infertility at 50 mg/kg-diet. Due to increased 

mortality in the control (14%, all females), there is concern with the ability to discern endocrinerelated effects seen in the mallard study.

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Table 3. Androgenic/Anti-Androgenic Pathway for Oxamyl 

Lines of Evidence Indicating Potential Interaction with the Androgenic/Anti-Androgenic Pathway for Oxamyl1Study Type / Literature Citation 

AR Binding 

Steroidogenesis 

Sex Steroid 

Hormones 

Testes 

Weight/GSI 

Gonad Staging 

and 

Histo

pathology

Epididymides 

Weight 

Epididymides 

Histopathology 

Pituitary Weight 

Accessory Sex 

Organ Weights / 

2° Sex Characterist

ics

Fertility (Frt) / 

Fecundity (Fcd) 

Age and Weight at 

PPS 

Vitellogenin 

EDSP Tier 1 Assay 

AR Binding (MRID 48672703) N Steroidogenesis (MRID 48686702) N Hershberger (MRID 48618402) NE N Male Pubertal Rat (MRID 48702103) N N N N N N N N FSTRA (MRID 48702101) NE 

GSI: 

↑30% 

(H) 

N N N N 

OSRI 

Two-generation reproduction (Rat; MRID 41660801) 

N N NE N NE NE N 

Chronic toxicity / carcinogenicity (Rat; MRID 41963101) 

N N NE N NE NE 

Carcinogenicity (Mouse; MRID 00076813) 

 N N NE N NR NR 

Chronic toxicity (Dog; MRIDs 41697901/ 42052701) 

N N NE N NE NE 
OXAMYL FIN

Page 15 of 48 

Table 3. Androgenic/Anti-Androgenic Pathway for Oxamyl 

Lines of Evidence Indicating Potential Interaction with the Androgenic/Anti-Androgenic Pathway for Oxamyl1Study Type / Literature Citation 

AR Binding 

Steroidogenesis 

Sex Steroid 

Hormones 

Testes 

Weight/GSI 

Gonad Staging 

and 

Histo

pathology

Epididymides 

Weight 

Epididymides 

Histopathology 

Pituitary Weight 

Accessory Sex 

Organ Weights / 

2° Sex Characterist

ics

Fertility (Frt) / 

Fecundity (Fcd) 

Age and Weight at 

PPS 

Vitellogenin 

Avian reproduction (Quail; MRID 00116610) 

N 

1. Key to responses: L=Low treatment, ML=Medium-low treatment, M=Medium treatment, MH=Medium-high treatment, H=High 

indicate the direction of the response. A shaded cell indicates that is parameter is not routinely evaluated or is not applicable in this are absolute unless otherwise indicated. Abbreviations for androgen sensitive tissues: Seminal vesicles (SV), Ventral prostate (VP)

Prostate (PR), Levator ani-bulbocavernosus (LABC), Epididymides (E), Cowper’s gland (CG), Glans penis (GP). 

2. The systemic toxicity in the Tier 1 assays are presented in this column (e.g. KW= kidney weight). The systemic toxicity for the OS

this column. For details see Section IV. A 

3. The overt toxicity in the Tier 1 assays are presented in this column (e.g. ↓BW). The overt toxicity for the OSRI is indicated by an X 

details see Section IV. A 

P Positive findings N Negative findings (in vitro) / No effect (in vivo) 

NE Not examined NR Not reported 
OXAMYL FINAL 

Page 16 of 48 

C. Effects on Hypothalamic-Pituitary-Thyroidal (HPT) Axis 

The current EDSP Tier 1 battery does not have a specific in vitro assay to detect chemicals with 

the potential to affect hypothalamic or pituitary regulation of thyroid hormone production, but it 

does include three in vivo assays that provide data to detect changes in the HPT axis, i.e., the 

pubertal female and male rat assays, and the AMA (frog). 

The potential for oxamyl to interact with thyroid regulation are summarized in Table 4. If an 

effect was observed but considered by WoE not to reflect a direct interaction, then the effect is 

discussed in the text but not presented in the table. The various targets of the thyroid pathway 

across the relevant Tier 1 assays are delineated so as to facilitate determination of potential for 

thyroid or HPT axis effects. This table also includes HPT-relevant findings from data evaluated 

as OSRI. Effects that occurred in the presence of overt toxicity are discussed in the text but are 

not reported in the table and not considered further in the WOE assessment. 

In both the female and male pubertal rat assays, no treatment-related effects were noted for 

thyroid histopathology, or serum T4 or TSH levels. A non-dose-dependent increase in thyroid 

weight was observed in low- (0.25 mg/kg/day) and high- (5 mg/kg/day) dose pubertal female rats 

(20 and 13%, respectively). There were no thyroid-related effects observed in the Part 158 

mammalian studies. 

In the AMA, oxamyl did not significantly alter 7- or 21-day hind-limb length (HLL), snout-vent 

length (SVL) or body weight at any treatment concentration. No treatment-related mortality was 

observed during the study, and no clinical signs of toxicity were noted. Although all of the 

surviving frogs were beyond NF stage 61 at test termination (termed “late-stage”) which may 

confound the ability to adequately evaluate potential thyroid-related effects in the AMA, there 

was no significant acceleration or delay of median NF developmental stage at any treatment 

concentration throughout the test nor effects on thyroid histopathology compared to the control. 

Therefore, there is no convincing evidence of potential thyroid-related interaction in the AMA 

for oxamyl. 

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OXAMYL FINAL 

Page 17 of 48 

Table 4. Thyroid Pathway for Oxamyl 

Lines of Evidence Indicating Potential Interaction with the Thyroid Pathway for Oxamyl1

Study Type / Literature 

Citation 

Thyroid Weight Thyroid: Gross and Histopathology Serum T4 Levels 

Serum TSH Levels Pituitary Weight Developmental stage (± or asynchronous, or HLL) Growth (BW, SVL) Systemic Toxicity Observed 2

Overt Toxicity Observed3 

EDSP Tier 1 Assays 

Female Pubertal Rat 

(MRID 48702104) N N N N N N N N

Male Pubertal Rat 

(MRID 48702103) N N N N N N N N

AMA 

(Frog; 

MRID 48702102) 

N N N N 

OSRI 

Developmental toxicity 

(Rat; MRID 40859201) 

X 

(H) 

X 

(H) 

Developmental toxicity 

(Rabbit; 

MRID 00063009) 

 N N 

Two-generation 

reproduction 

(Rat; MRID 41660801) 

NE X 

(H) 

X 

(M, H) 

Chronic toxicity / 

carcinogenicity 

(Rat; MRID 41963101) 

NE N NE X 

(MH, H)

X 

(MH, H) 

Carcinogenicity (Mouse; 

MRID 00076813) NE N NE N X 

(M, H) 

Chronic toxicity 

(Dog; MRIDs 41697901/ 

42052701) 

N N NE X 

(L, M, H) 

X 

(M, H) 

1. Key to responses: L=Low treatment, ML=Medium-low treatment, M=Medium treatment, MH=Mediumhigh treatment, H=High treatment. Arrows (↓ or ↑) indicate the direction of the response. A shaded cell 

indicates that is parameter is not routinely evaluated or is not applicable in this assay. Changes in weight 

are absolute unless otherwise indicated. 

2. The systemic toxicity in the Tier 1 assays are presented in this column (e.g. KW= kidney weight). The 

systemic toxicity for the OSRI is indicated by an X in this column. For details see Section IV. A 

3. The overt toxicity in the Tier 1 assays are presented in this column (e.g. ↓BW). The overt toxicity for the 

OSRI is indicated by an X in this column. For details see Section IV. A 

 N Negative findings 

 NE Not examined 

 

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OXAMYL FINAL 

Page 18 of 48 

IV. Committee’s Assessment of Weight of Evidence 

This section of the document describes the weight of evidence (WoE) determination on the 

potential of oxamyl to interact with endocrine related processes (i.e., E, A, or T hormonal 

pathways) as well as recommendations regarding Tier 2 testing. The results of the Tier 1 assays 

are considered, along with other scientifically relevant information (e.g., 40 CFR Part 158 test 

guidelines and published or publicly available peer-reviewed studies). WoE analysis in the 

context of the EDSP follows the Agency’s guidance (USEPA 2011) and is conducted on a caseby-case basis by first assessing the different lines of evidence (i.e., specific Tier 1 assays and 

OSRI), then performing an integrated analysis of those lines of evidence. 

The WoE evaluation includes considerations of biological plausibility of the findings from the 

different lines of evidence by examining the consistency, coherence, and interrelationships 

among the measured endpoints within and across studies. The available findings from standard 

toxicology studies on the substance may contribute to the WoE evaluation in helping elucidate if 

effects seen in the Tier 1 assay are related to perturbations of the endocrine system per se or 

alternatively a sequelae of systemic effects. Endocrine modes of action may elicit a number of 

phenotypic consequences other than those evaluated in the Tier 1 assays. 

Endocrine-related findings in the presence of overt toxicity may result in uncertainty as to 

whether or not the responses are related through an endocrine pathway, therefore non-endocrine 

toxic responses (including but not limited to mortality or body weight changes) are also 

considered in this WoE evaluation. The FIFRA SAP that evaluated scientific issues associated 

with weight of evidence evaluation of the results of the Tier 1 assays stated that “In summary, 

the Panel agreed that little, if any, weight should be placed on signs of endocrine disruption in 

the presence of overt toxicity. All effects in endocrine sensitive tissues should be evaluated in 

terms of primary interactions with the endocrine system vs. secondary effects related to toxicity 

in non-endocrine organs or overall disruptions in homeostasis” (USEPA, 2013). 

A. Systemic/Overt Toxicity in the in vivo Tier 1 Assays and OSRI 

Effects that were considered to be systemic or overt toxicity for the in vivo Tier 1 assays and 

OSRI studies are described below. In addition to the endocrine-related effects described above 

for the in vivo Tier 1 assays and OSRI, other effects observed which may be considered 

overt/systemic toxicity are also describe below. Generally, one parameter (i.e., death or >10% 

decrease in mammalian body weight) was sufficient for a dose/concentration to be considered 

overtly toxic. However, in other instances, more than one parameter was needed to determine 

overt toxicity. Effects which were considered to be signs of systemic toxicity were generally less 

severe forms of toxicity (e.g., organ weights, blood chemistry).

1. Tier 1 in vivo Assays 

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OXAMYL FINAL 

Page 19 of 48 

No overt toxicity was observed in any of the mammalian in vivo Tier 1 assays. In the female and 

male pubertal rat studies, there were generally no treatment-related changes in organ weights, 

macroscopic observations or histopathological observations in any examined organs. The only 

exception was an increased absolute and adjusted thyroid weights in the female pubertal rat 

study, without concomitant histopathological or hormonal effects. Although ChE activity was 

not determined in these studies and no clinical signs were observed at oxamyl doses up to 

0.5 mg/kg/day, this dose approximates the maximum tolerated dose (MTD) based on data from 

earlier studies showing decreases in brain and RBC ChE activity. 

In the FSTRA study, no effects on survival or clinical signs of toxicity were observed, but there 

was a significant decrease in female body weight in the high-concentration group 

(0.989 mg a.i./L) of 13% (body length was not determined). No overt or systemic signs of 

toxicity were observed in the AMA study at test concentrations up to 0.12 mg/L. 

2. OSRI 

In the developmental study with rats, there were no mortalities, but incidence of clinical signs 

was increased, including diarrhea (6/25), eye discharge (12/25), salivation (20/25), tremors 

(25/25), and wet legs - perineal and underbody (5–11/25) - during the treatment period in high 

dose animals, with a lower incidence (NS) of tremors at the medium-high dose (4/25). Although 

ChE activity was not determined in this study, these effects are consistent with ChE inhibition. 

Decreased body weight gain of 30 to 55% and decreases in food consumption were noted during 

treatment in most treatment groups except at the low dose. A body weight loss of 28% in the 

high dose group on GD 7 to 9. 

In the developmental study with rabbits, maternal absolute body weights and food consumption 

were generally comparable between the treated and control groups; however, during GD 6 to 19, 

the medium- and high-dose groups had decreased body weight gains compared to control (↓61.5 

and 67.2%, respectively). 

In a two-generation reproduction study with rats, increased incidences of a variety of clinical 

signs (alopecia, stained fur, hyperactivity and skin sores) in different sexes/generations at the 

high dose, but only the following were statistically significant (p<0.05): skin sores in F0 males, 

hyperactivity in F1 males, and alopecia in F1 females (also significant at medium dose). 

Treatment-related decreases in body weight were observed in the mid- and high dose groups 

during the premating phase, as well as gestation and lactation phases for females. Body weights 

for males and females in the F0 and F1 generations were decreased at the medium and high doses 

during the premating phase (70 or 105 days, respectively, of treated diet) in a dose-dependent 

manner. Body weights females in the F0 and F1 generations were decreased at the medium and 

high doses during the gestation and lactation phases of the study, with weight recovery observed 

during the lactation period. Similar decreases were noted for food consumption for high-dose 

Page 27 of 56
OXAMYL FINAL 

Page 20 of 48 

animals at the majority of the sampling intervals, and for medium-dose males; food consumption 

was generally comparable to control for medium-dose females. 

In the chronic toxicity study with rats, clinical signs included increased incidences of 

hyperactivity in the mid-high- and high-dose males/females, swollen legs/paws in mid- and highdose males and high-dose females, and skin sores or scabs in the medium-high- and high-dose 

females. Body weights were decreased in males in the medium-high dose (Day 7-470) and high 

dose (Day 7–680), and in females in the mid-high and high dose groups throughout the study 

(Day 7–722); decreases were consistently >10% in the high dose animals and in the mediumhigh females by Day 84 until study termination. Body weight in mid-high dose males was >10% 

during a portion of the first year, but later decreases ranged from 7–9% through Day 470. Mean 

body weight gains were decreased by 10–25%, respectively, in males, and female body weight 

gains were decreased by 27 to 37%, respectively, during the first year only. The decreased body 

weights and body weight gains were considered secondary to hyperactivity, because food 

consumption and food efficiency were not affected. In the medium-high- and high-dose groups, 

plasma ChE activities were decreased by 4 to 37% and 18 to 48%, respectively, in males, and by 

38% and 69%, respectively, in females after the first month of treatment only. Plasma ChE 

activities were not affected in the lower dose groups, and RBC and brain ChE activities were not 

decreased in any treated animals. 

In the carcinogenicity study with mice, mortality was increased early in the study (2 males, 9 

females at the medium dose: 14 males, 11 females at the high dose through Week 4). Due to 

these high mortality rates, the dose for the high-dose group was decreased at Week 6 from 100 to 

75 ppm, and extra animals were added to most of the dose groups. Overall survival at study 

termination was not significantly different for any treatment group compared to control. 

Apparent treatment-related effects on body weight were observed in this study in the mid- and 

high-dose groups, but body weight data were not presented in the available reviews; it was 

reported that decreased body weight in females was sporadic but persistent in males throughout 

the study. No treatment-related effect on food consumption was noted. Determination of ChE 

activity was not conducted in this study. 

In the chronic toxicity study with dogs, one female dog in the high-dose group died on study, but 

the cause of death was not determined. Increased incidences of clinical signs including tremors 

and vomiting were observed in animals in the medium- and high-dose groups. Mean body 

weights/body weight gains in high-dose males and females were decreased 23%/81% and 

17%/49%, respectively, at study termination. Body weight decreases in males and females were 

≥10% by Week 7, but decreases were only significant for the last 7 weeks of the study (male 

body weight) and for overall male body weight gain. In low-dose males, plasma ChE was 

inhibited at 6, 9, and 12 months by approximately 30% throughout the study; females exhibited 

minor decreases in plasma ChE at the same sampling times. Plasma ChE activity in the mediumand high-dose groups in males was decreased, but generally not dose-dependently, from Week 1 

Page 28 of 56
OXAMYL FINAL 

Page 21 of 48 

through study termination (approximately 50 to 70%). Decreases in plasma ChE activity in the 

medium- and high-dose females also were observed from Week 1 through study termination 

(approximately 30 to 60%). RBC ChE activity was not affected, and brain ChE activity was only 

decreased in males. No treatment-related effects were noted for any absolute organ weights. 

In a follow-up chronic dog study with lower doses to determine a NOAEL, no treatment-related 

clinical signs were present, and no mortality occurred. In addition, there were no treatmentrelated effects on body weight, body weight gain, food consumption, or organ weights. At study 

termination, plasma ChE at the high dose (50 ppm) was comparable to control and RBC ChE 

activity was decreased (↓22%), although RBC ChE activity throughout the study was variable. A 

decrease (↓20%, NS) in brain (cerebellum with medulla) ChE activity was noted in the high-dose 

group and is considered relevant, as tremors were observed at 150 and 250 ppm in males, and at 

all doses in females, in the previous study. In the medium-high-dose group, plasma, RBC, and 

brain ChE activities were decreased 18%, 5%, and 2%, respectively. 

In the Part 158 avian reproduction study with mallard ducks, mortality and observations of penmate aggression were observed in the control and all treatment groups. 

In a freshwater fish early life-stage test in rainbow trout, no treatment-related effects on embryo 

hatching, larval survival, first day of larval swim-up or larval growth was observed at test 

concentrations ≤0.77 mg/L. At 1.5 mg/L (the highest concentration tested), statistically 

significant (p<0.05) delays in the first day of embryo hatching (+2 days) and larval swim-up 

(+5 days) were observed, as well as a decrease (↓96%) in the percentage embryo hatching. 

B. Estrogen Pathway 

There was no convincing evidence of interaction of oxamyl with the estrogen pathway. The Tier 

1 in vitro assays were negative (ER binding, ERTA, aromatase and steroidogenesis assays), as 

well as the Tier 1 uterotrophic assay. In the female pubertal assay, while there were increases in 

uterine weights, the absence of complimentary data does not support estrogen-related etiology 

for this effect. There were also no treatment-related effects observed in the FSTRA. 

C. Androgen Pathway 

There was no convincing evidence of interaction of oxamyl with the androgen pathway. The Tier 

1 in vitro (i.e, AR binding and steroidogenesis) and Hershberger assays were negative. No 

androgen-related effects were observed in the Tier 1 male pubertal assays or mammalian Part 

158 studies. In the FSTRA assay, while there was an increase in GSI at high dose, no other 

effects were observed. 

D. Thyroid Pathway 

Page 29 of 56
OXAMYL FINAL 

Page 22 of 48 

There was no evidence of interaction of oxamyl with the thyroid pathway. Thyroid parameters 

were not altered in Tier 1 mammalian or amphibian in vivo studies, except for a non-dosedependent increase in thyroid weights in the female pubertal rat (20% and 13% at the mid and 

high dose, respectively). 

E. Conclusions 

Oxamyl demonstrates no convincing evidence of potential interaction with the estrogen, 

androgen, or thyroid pathways. 

V. EDSP Tier 2 Testing Recommendations 

Based on weight of evidence considerations, mammalian or wildlife Tier 2 testing is not 

recommended for oxamyl since there was no convincing evidence of potential interaction with 

the estrogen, androgen or thyroid pathways. 

 

Page 30 of 56
OXAMYL FINAL 

Page 23 of 48 

VI. References 

Adamik, E.R., Criswell, M.K., Mahler, S.C., et al. (1981). Long Term Feeding Study in Mice 

with Oxamyl: Project No. WIL-77033: HL0-252-81. (Unpublished study received May 29, 1981 

under 352-372: Unpublished study conducted by WIL Research Laboratories, Inc., submitted by 

E. I. du Pont de Nemours and Co., Wilmington, Delaware: COL: 070136-A, 070137, 070138, 

070139, 070140, 070141, 070142, 070143). (MRID 00076813). 

Dickrell, L. (1991). 52-Week dietary toxicity study with IN 01410-196 (oxamyl) in male dogs. 

Unpublished study conducted by Hazleton Laboratories, Inc.; Study No. HLO 555-90; Submitted 

to EPA by E. I. du Pont de Nemours and Co.; 10/3/91. (MRID 42052701). 

Fort, D.J. (2012). Oxamyl (DPX-D1410) Technical: 21-d Amphibian Metamorphosis Assay 

(AMA) with South African Clawed Frog, Xenopus laevis. Unpublished study conducted by Fort 

Environmental Laboratories, Inc., Stillwater, OK 74074. Laboratory report number DUPO01-

00270. Study sponsored by E. I. du Pont de Nemours and Company (DuPont), Wilmington, 

Delaware. May 31, 2012. (MRID 48702102). 

Hicks, S.L. (2012). Oxamyl Technical (DPX-D1410): Short-term Reproduction Assay with the 

Fathead Minnow, Pimephales promelas. Determined Under Flow-Through Conditions. 

Unpublished study conducted by Performed by ABC Laboratories, Inc., Columbia, Missouri and 

Experimental Pathology Laboratories, Inc., Sterling, Virginia, Report No.: 66763. Submitted by 

E. I. du Pont de Nemours and Company, Wilmington, Delaware. May 14, 2012. 

(MRID 48702101). 

Hobermam, A.M., Mossburg, P.A., Wolfe, G.W., et al. (1980). Teratogenicity Study in Rabbits. 

Unpublished study conducted by Hazleton Laboratory of America, Inc., Vienna, VA. Study No. 

201-405. October 1980. (MRID 00063009). 

Hurtt, M. (1990). Reproductive and Fertility Effects with Oxamyl (IN D1410): Multigeneration 

Reproduction Study in Rats: Lab Project Number: 423-90: 8433-88- 001. Unpublished study 

prepared by Haskell Laboratory / E. I. du Pont de Nemours and Co. (MRID 41660801). 

Hutton, D. G. (1988). Early Life Stage Toxicity of IN 01410-196 (Oxamyl) to Rainbow Trout·. 

Report No. 468-88. Unpublished study conducted by E. I. du Pont de Nemours and Company, 

Inc., Newark, Delaware; Submitted by E. I. du Pont de Nemours and Company, Inc., Newark, 

Delaware. (MRIDs 40901101 and 41472301). 

Malley, L. A. (1991). Combined chronic toxicity/ oncogenicity study with oxamyl (IN 01410-

196) long term feeding study in rats. Unpublished study conducted by Haskell Lab.; Study No. 

278-91. (July 11, 1991). Submitted to EPA by DuPont Agricultural Products. 

(MRID 41963101). 

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Mebus, C.A. (1990). Chronic toxicity study with oxamyl (IN 01410-196) one year feeding study 

in dogs. Unpublished study conducted by Haskell Lab.; Study No. 381-90. Submitted to EPA by 

E. I. du Pont de Nemours and Co. (MRID 41697901). 

Munley, S.M. (1998). DuPont’s Position on Fetal Weight Changes in Rats Following 

Developmental Toxicity Testing with Oxamyl. Unpublished study conducted by E. I. du Pont de 

Nemours and Company, Newark, Delaware. Medical Research No. 8428-001. December 16, 

1998. (MRID 44737501). 

Nabb, D.L. (2012). Oxamyl (DPX-D1410) Technical (98% w/w): H295R Steroidogenesis 

Assay. Unpublished study conducted by E. I. du Pont de Nemours and Company, Newark, DE. 

Laboratory report number DuPont-32077, Feb 8 2012. (MRID 48686702). 

Rickard, L. B. (1988). Teratogenicity Study of IN D1410-196 in the rat. Unpublished study 

conducted by Haskell Laboratory for Toxicology & Industrial Medicine. Medical Research No. 

8424-001; Lab. Project. No. 473-88. October 3, 1988. (MRID 40859201). 

Roberts, N.L., Phillips, C.N.K., Chanter, D.O., McAllister, A. (1982a). The effects of dietary 

inclusion of oxamyl on reproduction in the mallard duck. DuPont Report No.: HLO 337-82, 

USEPA guideline 163.71-4 (1978). (MRID 00116609). 

Roberts, N.L., Phillips, C.N.K., Chanter, D.O., McAllister, A. (1982b). The effects of dietary 

inclusion of oxamyl on reproduction in the bobwhite quail. DuPont Report No.: HLO 453-82, 

USEPA guideline 163.71-4 (1978). (MRID 00116610). 

Snajdr, S. (2011). Oxamyl (DPX-D1410) Technical (98% w/w): 10-Day Hershberger Bioassay 

for Detecting Androgenic Activity. Unpublished study conducted by E. I. du Pont de Nemours 

and Company, DuPont Haskell Global Centers for Health & Environmental Sciences, Newark, 

DE. Laboratory Project ID: DuPont-32076, November 8, 2011. (MRID 48618402). 

Snajdr, S.I. (2011). Oxamyl (DPX-D1410) Technical (98% w/w): In Vitro Aromatase Inhibition 

Using Human Recombinant Microsomes. Unpublished study conducted by DuPont Haskell 

Global Centers for Health and Environmental Sciences, Newark, DE. Laboratory Project ID: 

DuPont-32072, January 5, 2012. (MRID 48672701). 

Snajdr, S.I. (2011). Oxamyl (DPX-D1410) Technical (98% w/w): 3-Day Uterotrophic Assay for 

Detecting Estrogenic Activity. Unpublished study conducted by DuPont Haskell Global Centers 

for Health & Environmental Sciences, Newark, DE. Laboratory Project ID: DuPont-32075, 

November 8, 2011. (MRID 48618401). 

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Snajdr, S.I. (2012). Oxamyl (DPX-D1410) Technical (98% w/w): In Vitro Androgen Receptor 

Binding Assay Using Rat Prostate Cytosol. Unpublished study conducted by DuPont Haskell 

Global Centers for Health & Environmental Sciences, E. I. du Pont de Nemours and Company, 

Newark, DE. Laboratory Project ID: DuPont-32153, January 6, 2012. (MRID 48672703). 

Snajdr, S.I. (2012). Oxamyl (DPX-D1410) Technical (98% w/w): In Vitro Estrogen Receptor 

Binding Assay Using Rat Uterine Cytosol (ER-RUC). Unpublished study conducted by DuPont 

Haskell Global Centers for Health & Environmental Sciences, E. I. du Pont de Nemours and 

Company, Newark, DE. Laboratory Project ID: DuPont-32074, January 5, 2012. 

(MRID 48672702). 

Toot, J. (2012). Pubertal Development and Thyroid Function in Intact Juvenile/Peripubertal 

Female Rats following Oral Administration of Oxamyl (DPX-D1410) Technical (98% w/w). 

Unpublished study conducted by WIL Research, Ashland, OH. Laboratory Project ID: WIL189243, June 5, 2012. (MRID 48702104). 

Toot, J. (2012). Pubertal Development and Thyroid Function in Intact Juvenile/Peripubertal 

Male Rats following Oral Administration of Oxamyl (DPX-D1410) Technical (98% w/w). 

Unpublished study conducted by WIL Research, Ashland, OH. Laboratory Project ID: WIL189244, June 5, 2012. (MRID 48702103). 

USEPA (2010). Oxamyl — Report of the Endocrine Disruptor Review Team; Test Order # 

EDSP-103801-63. December 6, 2010. Office of Chemical Safety and Pollution Prevention. 

U.S. Environmental Protection Agency, Washington, D.C. 

USEPA. (2011). Endocrine Disruptor Screening Program — Weight of Evidence: Evaluating 

Results of EDSP Tier 1 Screening to Identify the Need for Tier 2 Testing. Office of Chemical 

Safety and Pollution Prevention. U.S. Environmental Protection Agency, Washington, DC. 

USEPA (2013) Transmittal of Meeting Minutes of the FIFRA Scientific Advisory Panel Meeting 

held July 30 - August 1, 2013 on Weight-of-Evidence: Evaluating Results of EDSP Tier 1 

Screening. Office of Chemical Safety and Pollution Prevention. U.S. Environmental Protection 

Agency, Washington, DC. 

Willoughby, J.A. (2012). Oxamyl (DPX-X1410) Technical: Estrogen Receptor Transcriptional 

Activation (Human Cell Line (HeLa-9903)). Unpublished study conducted by CeeTox, 

Kalamazoo, MI. Laboratory Report No.: 9144V-100359ERTA, Feb 7, 2012. (MRID 48686701). 

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APPENDIX 1. EDSP Tier 1 Screening Assays 

Amphibian Metamorphosis Assay (AMA): (OCSPP 890.1100) 

The 21-day assay (MRID 48702102) of oxamyl (DPX-D1410) on amphibian metamorphosis of 

South African clawed frogs (Xenopus laevis) was conducted under flow-through conditions. 

Amphibian larvae at Nieuwkoop-Faber (NF) Stage 51 (80/control and treatment group; 

20/replicate) were exposed to oxamyl (98.0% purity) at nominal concentrations of 0 (negative 

control), 0.013, 0.040, and 0.120 mg a.i./L; time-weighted, mean-measured concentrations were 

<0.0085 (<LOD; negative control), 0.0106, 0.0399, and 0.1301 mg a.i./L. The test system was 

maintained at 22.4 to 22.9°C and a pH of 6.8 to 7.7. 

No treatment-related mortality was observed during the study, with mortalities of 1.7, 3.3, 0, and 

3.3% in the control, low, mid, and high treatment groups, respectively. No clinical signs of 

toxicity were noted in any tadpoles at test termination. There were no effects (p>0.05) on body 

weight or snout-vent length at any of the treatment levels compared to the negative control. 

Oxamyl did not significantly increase or decrease (p>0.05) Day 7 or Day 21 normalized (to 

snout-vent length) hind-limb length (HLL) at any treatment level. Furthermore, there was no 

significant acceleration or delay (p>0.05) of median NF developmental stage at any treatment 

level throughout the test, though all surviving tadpoles at Day 21 were late-stage (NF≥61). No 

asynchronous development was observed. Mild follicular cell hyperplasia and hypertrophy were 

observed in the negative control and all treatment groups, though there was no apparent 

treatment-related effect in incidence. Follicular cell height and area were not determined. 

Although all of the surviving frogs were beyond NF stage 61 at test termination which may 

confound the ability to adequately evaluate potential thyroid-related effects in the AMA, there 

was no significant acceleration or delay of median NF developmental stage at any treatment 

concentration throughout the test, and there were no effects on thyroid histopathology compared 

to the control. 

Androgen Receptor (AR) Binding Assay; (OCSPP 890.1150) 

In an androgen receptor (AR) binding assay (MRID 48672703), ventral prostate cytosol from 

castrated Sprague Dawley rats was used as the source of AR to conduct a saturation binding 

experiment and a competitive binding experiment. The saturation binding experiment was 

conducted to demonstrate that the AR in the rat prostate cytosol was present in reasonable 

numbers and was functioning with appropriate affinity for the radiolabeled reference androgen 

(R1881) prior to routinely conducting AR competitive binding experiments. The competitive 

binding assay was conducted to measure the binding of a single concentration of [3

H]-R1881 (1 

nM) in the presence of increasing concentrations (logarithmic increase from 10-10 to 10-3 M) of 

oxamyl (98.0% purity, Lot #6689-176-5). Deionized water was used as the vehicle for oxamyl, 

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and ethanol was used for the reference chemicals, at a final concentration of 3%. A total of four 

runs were performed, and each run included dexamethasone as a weak positive control, and 

R1881 as the ligand reference standard. 

In the saturation binding experiment, the maximum binding capacity (Bmax) was 4.5 fmol/100 μg 

protein and the dissociation constant (Kd) was 0.903 nM. The Kd was within the range reported 

in the EPA validation program, but the Bmax was below the EPA values. The Scatchard plots for 

the three saturation assays were linear. 

In the competitive binding experiment, the estimated average log IC50 was −9.05 M for R1881 

and −4.37 M for the weak positive control (dexamethasone). Compared to R1881, the mean 

RBA for the positive control was 0.0022%. One run was repeated. Although the performance 

criteria for both R1881 and dexamethasone were not achieved across the three runs, based on the 

estimated IC50s for R1881 and the weak positive control, the androgen receptor was present in a 

reasonable concentration and functioning with appropriate affinity for the ligand in the 

competitive binding assays. It is unlikely that information from additional competitive binding 

runs would change the interpretation of this study. 

Oxamyl had no effect on specific binding of the [3

H]-ligand; therefore, a log IC50 and RBA could 

not be calculated for oxamyl as it did not result in 50% reduction in ligand binding at any 

concentration. 

Based on the results from the three runs, methomyl is classified as a Non-Binder in the Androgen 

Receptor Binding Assay. 

Aromatase Assay; (OCSPP 890.1200) 

In an in vitro aromatase (CYP 19) assay (MRID 401), oxamyl (98.0% a.i., Lot#: 6689-176-5) 

was incubated with human recombinant aromatase and tritiated androstenedione (1-β [3

H(N)]-

androst-4-ene-3,17-dione; [3

H]ASDN) in water at log concentrations of 10−10 to 10−3 M for 15 

minutes to assess the potential of oxamyl to inhibit aromatase activity. 

Aromatase activity was determined by measuring the amount of tritiated water produced at the 

end of a 15-minute incubation for each concentration of chemical. Tritiated water was quantified 

using liquid scintillation counting (LSC). A total of four runs were conducted and each run 

included full enzyme activity controls, background activity controls, a positive control series 

(10−10 to 10−5

 M) using a known inhibitor (4-hydroxyandrostenedione; 4-OH ASDN), and the 

oxamyl series (10−10 to 10−3 M) with three replicates per concentration. Because the solvent 

vehicle was water for oxamyl and dimethyl sulfoxide (DMSO) for 4-OH ASDN, separate sets of 

the background activity and full enzyme activity controls were run using only water or 1% 

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DMSO (final concentration in assay). In the second run, the full activity controls (water only) 

had aromatase activity below the performance criteria specified in the Guideline; therefore, the 

second run was excluded from the calculations and a fourth run was performed. 

Aromatase activity in the full activity controls for the three successful test runs ranged 0.201-

0.532 nmol·mg-protein−1·min−1 in water only with a mean and standard deviation of 0.344±0.112 

nmol·mg-protein−1

·min−1, and 0.242-0.631 nmol·mg-protein−1·min−1 in 1% DMSO with a mean 

and standard deviation of 0.437±0.119 nmol·mg-protein−1

·min−1. Activity in the background 

controls averaged 0.62% of full activity controls in water and 0.54% of full activity controls in 

1% DMSO. The response of each full activity control was generally between 90 to 110% of the 

average full activity, with only a few minor exceptions. 

For the positive control substance (4-OH ASDN), aromatase activity averaged 0.436±0.096 

nmol·mg-protein−1

·min−1 at the lowest tested concentration (10−10 M) and 0.004±0.001 nmol·mgprotein−1

·min−1 at the highest tested concentration (10−5 M). These results were generally within 

the recommended ranges for the top of the curve, bottom curve, Hill Slope, log IC50, and 

coefficient of variation (CV) for replicates of each concentration, with the following exceptions: 

the overall %CV for concentrations between 10−7.5 M and 10−5

 M (16.5 to 21.5%) exceeded the 

acceptable limit of 15%, and the top of the curve in Run 1 (115%) exceeded the recommended 

range (90 to 110%). 

For oxamyl, aromatase activity averaged 0.370±0.111 nmol·mg-protein−1·min−1 at the lowest 

tested concentration (10−10 M) and 0.351±0.115 nmol·mg-protein−1·min−1 at the highest tested 

concentration (10−3

 M). The lowest portion of the response curve was greater than 75% activity 

at concentrations from 10−10 M to 10−3 M oxamyl across all runs. 

Based on the data from the average response curve, oxamyl is classified as a Non-inhibitor of 

aromatase activity in this assay. 

Estrogen Receptor (ER) Binding Assay; (OCSPP 890.1250) 

In an estrogen receptor (ER) binding assay (MRID 48672702) for oxamyl (98.0% purity, Lot 

#6689-176-5), uterine cytosol from ovariectomized Sprague Dawley rats was used as the source 

of estrogen receptors (ER) to conduct saturation binding experiments and competitive binding 

experiments in this assay. The saturation binding experiment was conducted to demonstrate that 

the ER in the rat uterine cytosol was present in reasonable numbers and was functioning with 

appropriate affinity for the radiolabeled reference estrogen prior to routinely conducting ER 

competitive binding experiments. The competitive binding experiment was conducted to 

measure the binding of a single concentration of [3

H]-17β-estradiol (1 nM) in the presence of 

increasing concentrations (logarithmic increase from 10−10 to 10−3 M) of oxamyl. Deionized 

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water was used as the vehicle for oxamyl, and ethanol was used for the reference chemicals, at a 

final concentration of 2%. A total of three runs were performed, and each run included 19-

norethindrone as a weak positive control, octyltriethoxysilane as a negative control, and 17βestradiol as the natural ligand reference material. 

In the saturation binding experiment, the mean maximum binding capacity (Bmax) was 32.5 

fmol/100 μg protein and the mean dissociation constant (Kd) was 0.081 nM. These values were 

within the recommended ranges, and the Scatchard plots for the three saturation assays were 

linear. The specific binding reached a plateau, and non-specific binding (NSB) was less than 

20% of total binding (4 to 12%). The saturation binding experiment demonstrated that the 

estrogen receptor was present in a reasonable concentration and functioning with appropriate 

affinity for the reference ligand 17β-estradiol. 

In the competitive binding experiment, the estimated mean log IC50 was -9.16 M for 17βestradiol and -4.85 M for the weak positive control. The mean RBA was 0.0054% for the weak 

positive control. Performance criteria were not met for 17β-estradiol top % binding (76% for 

Run 1) and the bottom % binding for 19-norethindrone was considerably lower in Run 2 

(-22.1%) compared to the values for the other two runs. However, the Hill slope values were 

consistent in the three competitive binding experiments and were within the range of the values 

classically obtained during the validation program of the assay, indicating one-site competitive 

binding. 

Oxamyl had no effect on specific binding of the [3H]-ligand; therefore, a log IC50 and RBA could 

not be calculated for oxamyl; the percent labeled estradiol bound to the ER was >75% at all 

concentrations of oxamyl tested. Based on the results from the three runs, oxamyl is classified as 

Not Interactive in the Estrogen Receptor Binding Assay. 

ERα Transcriptional Activation (ERTA) Assay; (OCSPP 890.1300) 

In an estrogen receptor transcriptional activation assay (MRID 48686701), hERα-HeLa-9903 

cells cultured in vitro were exposed to oxamyl (98.0% a.i. Lot # 16995) at logarithmically 

increasing concentrations from 10−10.3 to 10−3.3 M in water for 24 hours in two independent runs. 

The experiments were performed using 96-well plates and each oxamyl concentration was tested 

in 6 wells/plate in each run. Cells were exposed to the test agent for 24±2 hours at 37±1°C to 

induce reporter (luciferase) gene products. Luciferase expression in response to activation of the 

estrogen receptor by oxamyl was measured upon using a proprietary luciferase assay. 

Oxamyl was tested up to the limit of cytotoxicity, which was observed at 10-4.3 M in the first run. 

In the main assays, the responsiveness of the cells to the very weak positive control 17αmethyltestosterone was lower than the expected values, indicating a decreased sensitivity of the 

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assay to very weak agonists. Although the conditions of this assay were not optimal to detect 

very weak activity, oxamyl responses were similar to those of the negative control corticosterone 

and not comparable to the responses of 17α-methyltestosterone, which was able to reach a 

maximum of 24.3-26.6% PC. Oxamyl was only able to reach a maximum of 2.9-4.4% PC when 

tested up to the highest concentration possible based on cytotoxicity (10-5.3 M). Because the 

RPCMax < PC10 in both assay runs, oxamyl was considered negative for estrogen receptor 

transcriptional activation in this test system. 

Fish Short Term Reproduction Assay (FSTRA); (OCSPP 890.1350) 

The 21-day short-term reproduction assay (MRID 48702101) of oxamyl with fathead minnows 

(Pimephales promelas) was conducted under continuous flow-through conditions. Adult fish (16 

spawning groups, 2 males and 4 females in each group; 5.5 months old) were exposed to oxamyl 

(98.0% purity) at nominal concentrations of 0 (negative control), 0.090, 0.30, and 1.0 mg a.i./L; 

mean-measured concentrations were <LOD (<0.0085, negative control), 0.0866, 0.305, and 

0.989 mg a.i./L. The test system was maintained at 24.6 to 25.1o

C and a pH of 7.64 to 8.27. 

Adult male and female survival were unaffected by treatment. In the negative control, low, mid, 

and high treatment groups, male survival was 88, 88, 100, and 88%, respectively, and female 

survival was 100, 94, 94, and 88%, respectively. There were no notable observations with 

regards to behavior or changes in ovipositor appearance or size of dorsal nape pad in the negative 

control or treated groups. One male in the high treatment group periodically displayed signs of 

spinal curvature during the chemical exposure, and a second male in this treatment exhibited 

edema at test termination. Starting after Day 9 of the exposure, females displaying vertical 

banding were occasionally observed in the negative control and all treated groups, but the 

number of these observed females was not more than three per treatment. There was a 

significant decrease (p<0.05) in female body weight of 13.3% at the high treatment level 

compared to the negative control. Fish lengths at test termination were not reported. 

Fecundity in the negative control was 51 eggs/female/day/replicate (range: 45-59), and 

fertilization success averaged 91%. There was a significant increase (p<0.05) of 30% in male 

gonado-somatic index (GSI) at the high treatment level compared to the negative control. There 

were no apparent differences between gonadal stages in treated groups compared to the negative 

control. There were no significant differences between the treatment levels and negative control 

for any other endpoint. Plasma sex steroid hormones were not measured. 

Histopathological findings in males were unremarkable; minimal testicular degeneration was 

reported in one male fish in the negative control and high treatment group. Increased oocyte 

atresia was observed in 44, 20, 33, and 29% of females in the negative control, low, mid, and 

high concentration groups, respectively. This lesion was characterized as minimal to mild with 

moderate severity in one female from the negative control and mid treatment group and two 

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females from the low and high treatment groups. Minimal to mild granulomatous inflammation 

of the ovary was present in the negative control (25%), low (27%), mid (13%), and high (7%) 

treatment groups. In some instances, granulomatous inflammation was associated spatially with 

the presence of microsporidia fungi, although it is suspected that most, if not all, of the 

inflammation was induced by these organisms. According to the histological report, it did not 

appear that the presence of either microsporidia or inflammation had any effect on the study 

results. 

 

Hershberger Assay; (OCSPP 890.1400) 

The Hershberger Assay consists of androgenic and anti-androgenic components. To screen for 

potential androgenic activity, oxamyl (98.0% a.i., lot # 6689-176-5) in deionized water was 

administered daily via oral gavage to groups of 56-day old, castrated male Sprague Dawley rats 

(6/group) at dose levels of 0 (vehicle), 0.1, 0.25, or 0.5 mg/kg/day. An androgenic positive 

control group consisted of 6 castrated rats exposed to 0.4 mg/kg/day testosterone propionate (TP) 

in corn oil by subcutaneous injection. 

To screen for potential anti-androgenic activity oxamyl (98.0% a.i., lot # 6689-176-5) in 

deionized water was administered daily via oral gavage to 56-day old, castrated male Sprague 

Dawley rats (6/group) at dose levels of 0.1, 0.25, or 0.5 mg/kg/day in conjunction with a daily 

dose of reference androgen TP in corn oil at 0.4 mg/kg/day by subcutaneous injection. An antiandrogenic positive control group consisted of 6 castrated rats exposed to 0.4 mg/kg/day TP in 

corn oil and 3.0 mg/kg/day flutamide (FT) in 0.5% methylcellulose. TP alone was used as the 

anti-androgenic negative control. 

For both components of the assay, the animals were dosed for 10 consecutive days and 

necropsied approximately 24 hours after the final dose administration to determine weights of 

liver and the five androgen-dependent tissues. 

All animals survived until scheduled termination. There were no clinical signs of toxicity and no 

treatment-related gross pathological findings. 

In the androgen agonist assay, body weight and body weight gains for the 0.1, 0.25, and 0.5 

mg/kg/day treatment groups were comparable to controls throughout the duration of the assay. 

Animals dosed with TP had increased body weights on days 10-11 (↑7%) and increased 

cumulative body weight gains (p<0.05) for days 1-11 (↑25%). No effects on mean daily food 

consumption or food efficiency were observed in the 0.1, 0.25, and 0.5 mg/kg/day groups. 

Animals dosed with TP had increased mean daily food consumption (p<0.05) for days 1-11 

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(↑10%). No significant increases in the organ weights were observed in any of the five 

accessory sex tissues of animals dosed with oxamyl. Animals in the TP group displayed the 

expected increases (p<0.05) in accessory sex organ weights as follows: 699% in seminal 

vesicles; 768% in ventral prostate; 196% in levator ani-bulbocavernosus (LABC); 465% in 

Cowper’s gland; and 37% in glans penis. The performance criteria indicated that this assay was 

performing as expected. 

In the anti-androgen assay, there were no significant effects on body weights or body weight 

gains for any dose group. For the positive control group (TP + FT), cumulative body weight 

gains were decreased for days 1-11 (↓16%). No effects on mean daily food consumption or food 

efficiency were observed in the 0.1 and 0.5 mg/kg/day groups, or the positive control group. At 

0.25 mg/kg/day, mean daily food consumption was decreased (p<0.05) for days 1-11 (↓10%) 

however, food efficiency for the 0.25 mg/kg/day group was comparable to the controls. No 

significant decreases in organ weights were observed in any of the accessory sex tissues of the 

oxamyl-treated animals. Animals dosed with TP + FT displayed the expected decreases (p<0.05) 

in accessory sex organ weights as follows: 73% in seminal vesicles; 48% in LABC; 59% in 

Cowper’s gland; and 25% in glans penis. 

The maximum guideline-specified CVs were exceeded for the ventral prostate CV in the 0.1 

mg/kg/day group (46% vs. 40%), the LABC in 0.25 mg/kg/day (26% vs. 20%) and the positive 

control (28% vs. 20%) groups, and the glans penis in the positive control (21% vs. 17%) group. 

All other CV values were less than the maximum recommended values as indicated in the test 

guideline. 

The high dose of oxamyl selected for this study (0.5 mg/kg/day) is adequate based on data from 

earlier studies showing decreases in brain and red blood cell cholinesterase activity at dose levels 

ranging from 0.75-2.0 mg/kg/day. 

Statistically significant changes were not seen in two or more of the androgen sensitive tissue 

weights. Oxamyl was negative for androgenicity and anti-androgenicity in the Hershberger 

assay. 

Female Pubertal Assay; (OCSPP 890.1450) 

In a Female Pubertal Assay (MRID 48702104), 15 Sprague Dawley rats/dose group were treated 

daily by oral gavage with oxamyl (98.0% a.i., Lot #6689-176-5) in deionized water at doses of 0 

(vehicle), 0.25, or 0.5 mg/kg/day from post-natal day (PND) 22 to 42 or 43. Animals were 

examined for vaginal opening (VO) daily beginning on PND 22, and age and weight at day of 

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attainment were recorded. After sacrifice on PND 42 or 43, blood was collected for creatinine, 

urea nitrogen, and thyroid hormone analyses. Total thyroxine (T4) levels were determined using 

an electrochemiluminescent immunoassay and thyroid stimulating hormone (TSH) levels were 

determined using a radioimmunoassay. Adrenal, liver, pituitary, thyroid, and urogenital organs 

were weighed, and microscopic examinations were performed on the ovaries, uterus, thyroid, and 

kidneys. 

All animals survived until scheduled sacrifice. There were no treatment-related clinical signs of 

toxicity, and no treatment-related effects were noted on final body weights, body weight gain, 

mean age at first vaginal estrus, percent cycling, or the concentrations of serum T4, TSH, 

creatinine, or urea nitrogen. There were no treatment-related macroscopic observations or 

histopathological changes in the ovaries, uterus, thyroid glands, or kidneys. There were no 

treatment-related effects on the weights of liver, kidneys, pituitary, adrenals, or ovaries. 

The age at attainment of VO was decreased (p<0.05) by 1.8 and 1.7 to 1.8 days at 0.25 and 0.5 

mg/kg/day, respectively. However, these decreases were not dose-dependent. In addition, there 

was a 9% decrease (p<0.05) in body weight at VO at 0.5 mg/kg/day. 

Compared to the vehicle control, wet and blotted uterus weights were increased by 62 and 43% 

(p<0.01) at 0.25 mg/kg/day and by 34 and 28% (p<0.05) at 0.5 mg/kg/day. These differences 

were not dose-dependent and were attributed to differences in the animal’s stage of estrus at 

necropsy. Considering only the regularly cycling animals, the number of females in the 

proliferative phase of estrus (diestrus or proestrus) was one in the control, eight in the 0.25 

mg/kg/day group, and three in the 0.5 mg/day group, and the number of animals in the nonproliferative phase was ten in the control, six in the 0.25 mg/kg/day group, and seven in the 0.5 

mg/day group. Animals in the proliferative phase in each group were shown to have uterine 

weights that were greater than animals in the non-proliferative phase of the same group; this 

result is expected based on the increase in cell proliferation and accumulation of luminal fluid 

that occurs during the proliferative phase. Accordingly, the low number of control animals in the 

proliferative phase biased the results. 

When the phase of estrus at necropsy is taken into account, wet and blotted uterine weights 

(unadjusted) for animals in the proliferative phase were increased by 48 and 23%, respectively, 

in the 0.25 mg/kg/day group and by 54 and 34% for the 0.5 mg/kg/day group, compared to the 

control (single animal). For animals in the non-proliferative phase, wet and blotted uterine 

weights were increased respectively by 23 and 23% in the 0.25 mg/kg/day group and 26 and 

27% in the 0.5 mg/kg/day group, compared to the control (10 animals). Although there was an 

increase in uterine weights that appears to be dose-dependent, the differences in uterus weights 

between groups was not significant (NS). Therefore, the observed differences were attributed to 

normal biological variation in the animals. 

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Although the differences were not significant, at 0.5 mg/kg/day, the mean cycle length was also 

increased to 5.8 days from 4.9 day (control), the percent of females regularly cycling was 54.5% 

compared to 69.2% in controls, and the number of females in estrus was six compared to two in 

control group. In the absence of any other clear effect on the reproductive system, these 

differences may have been incidental. 

Absolute and adjusted thyroid weights were increased by 19 to 20% (p<0.05) at 0.25 mg/kg/day 

and by 12 to 13% (NS) at 0.5 mg/kg/day. Although these changes are substantial, the relevance 

of these weight changes are unclear as they were not dose-dependent and there were no 

associated changes in thyroid histology or hormone concentrations. 

The high dose selected for this study (0.5 mg/kg/day) was considered adequate based on data 

from earlier studies showing decreases in brain and red blood cell cholinesterase (ChE) activity 

at dose levels ranging from 0.75 to 2.0 mg/kg/day. 

Male Pubertal Assay; (OCSPP 890.1500) 

In a Male Pubertal Assay (MRID 48702103), 15 Sprague Dawley rats/dose group were treated 

daily via oral gavage with oxamyl (98.0% a.i., Lot #6689-176-5) in deionized water at doses of 0 

(vehicle), 0.25, or 0.5 mg/kg/day from post-natal day (PND) 23 to 53 or 54. Animals were 

examined for preputial separation (PPS) daily beginning on PND 30 and age and weight at day 

of attainment were recorded. Following sacrifice on PND 53 or 54, blood was collected for 

creatinine, urea nitrogen, and thyroid hormone analyses. Total thyroxine (T4) and testosterone 

levels were determined using an electrochemiluminescent immunoassay and thyroid stimulating 

hormone (TSH) levels were determined by radioimmunoassay. Adrenal, liver, pituitary, thyroid, 

and urogenital organs were collected and weighed, and microscopic examinations were 

performed on the testes, epididymides, thyroid, and kidneys. 

All animals survived until scheduled sacrifice. There were no treatment-related clinical signs of 

toxicity, and no treatment-related effects were noted on final body weights, body weight gain, 

age at PPS, body weight at PPS, or the levels of serum T4, TSH, testosterone, creatinine, or urea 

nitrogen. There were no treatment-related macroscopic observations or histopathological 

changes in the testes, epididymides, thyroid glands, or kidneys. There were no treatment-related 

effects on the weights of liver, pituitary, adrenals, seminal vesicles, ventral prostate, dorsolateral 

prostate, LABC, epididymis, testes, or thyroid. 

At 0.25 mg/kg/day, relative kidney weight was increased (p<0.05) by 6% compared to the 

controls, but the unadjusted and adjusted kidney weights at 0.25 and 0.5 mg/kg/day were similar 

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to controls. This minor change in relative kidney weight is not considered treatment-related as it 

occurred only at the low dose and was not associated with any macro- or microscopic finding. 

The high dose of oxamyl selected for this study (0.5 mg/kg/day) was adequate based on data 

from earlier studies showing decreases in brain and red blood cell cholinesterase activity at dose 

levels ranging from 0.75-2.0 mg/kg/day. 

Steroidogenesis Assay; (OCSPP 890.1550) 

In a steroidogenesis assay (MRID 48686702), H295R cells cultured in vitro in 24-well plates 

were incubated with oxamyl (98.0% a.i., Lot # 6689-176-5) at log concentrations from of 0.0001 

to 100 μM for 48 hours in triplicate for three independent experiments. Dimethyl sulfoxide 

(DMSO) was used as the vehicle for the positive controls and water was used as the vehicle for 

oxamyl. 

Testosterone and estradiol levels were measured using HPLC/MS/MS. A Quality Control (QC) 

plate was run concurrently with each independent run of a test chemical plate to demonstrate that 

the assay responded properly to positive control agents at two concentration levels; positive 

controls included the known inhibitor (prochloraz) and inducer (forskolin) of estradiol and 

testosterone production. 

The minimum basal hormone production levels for testosterone (500 pg/mL) were met in both 

blank and solvent control (SC) wells for testosterone. However, the minimum basal production 

for estradiol was below the recommended concentration of 40 pg/mL, except for the blank and 

SC in Run 1. Although the basal estradiol production as generally <40 pg/mL, all values were 

>12.5 pg/mL (2.5-fold greater than the minimum detection limit (MDL) as per the Guideline 

recommendation). Estradiol production was induced by forskolin by ≥7.5-fold, but induction of 

testosterone production (1.76- to 1.80-fold) was slightly below the Guideline specified ≥2-fold 

requirement. Testosterone and estradiol inhibition by prochloraz was >50% as required. 

Because all other guideline requirements for basal concentrations and hormone induction and 

inhibition were met for testosterone and estradiol, the performance criteria were deemed 

acceptable. 

The variability (%CV) between the runs based on the absolute concentrations of the SC was 

20.9% for testosterone and 23.5% for estradiol, which is within the recommended limit of ≤30%. 

The %CVs within each run for the QC plates were 0.04-15.64%. 

Precipitation was not observed at any tested oxamyl concentration, and oxamyl was not overtly 

cytotoxic to the H295R cells. Cell viability for the QC and test plates was ≥91% at ≤10μM of 

oxamyl, and 86.3-93.5% at 100 μM. No effect on estradiol production was observed at oxamyl 

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concentrations ≤100 μM. Slightly decreased testosterone levels were observed at 100μM 

oxamyl (approximately 0.8- to 0.9-fold; p≤0.05). This decrease was accompanied by a decrease 

in viability that could account for the slightly lower testosterone production at 100 μM. 

Adjusting for the 86.3-93.5% viability, the fold change in testosterone production at 100 μM 

oxamyl becomes 0.87-, 0.94- and 0.93-fold for Runs 1-3, respectively, and averaged 0.91-fold. 

Based on hormone responses in three independent runs, oxamyl treatment did not result in 

statistically significant and reproducible alterations in testosterone or estradiol production. 

Uterotrophic Assay; (OCSPP 890.1600) 

In an uterotrophic assay (MRID 48618401) conducted to screen for potential estrogenic activity, 

oxamyl (98% a.i., Batch # DPX-D1410-196) in deionized water was administered daily via oral 

gavage to groups of ovariectomized female Sprague-Dawley rats (6/group) at dose levels of 0 

(vehicle), 0.1, 0.25, or 0.5 mg/kg/day on post-natal days (PND) 67-69. A positive control group 

was treated with 17α-ethynyl estradiol (EE) by daily oral gavage at a dose level of 0.1 

mg/kg/day. All animals were terminated and necropsied on PND 70 approximately 24 hours 

after the final dose to determine wet and blotted uterine weights. 

All animals survived until scheduled termination. No clinical signs of toxicity were observed in 

any dose group. No treatment-related effects on the stage of estrous over the duration of the 

study were observed for oxamyl. All rats in the negative control and oxamyl treated groups were 

determined to be in diestrus during Days 1-4. Rats in the positive control group (EE) showed 

effects on the stage of estrus on Days 3 and 4. By Day 4, two of six rats in the positive control 

group showed cytological markers indicative of estrus and three of six rats showed markers 

indicative of proestrus. 

Body weights in the oxamyl treated groups were comparable to the controls throughout the 

duration of the assay. In the positive control group (EE), body weights were decreased (p<0.05) 

by 7% on Study Day 4 compared to controls and these animals actually lost weight (-7.6 g, 

p<0.05) compared to controls (12.2 g). 

No treatment-related effects on food consumption or food efficiency were noted in the oxamyl 

treated groups. In the positive control group (EE), overall (Days 1-4) food consumption was 

decreased (p<0.05) by 29% compared to controls and food efficiency was -0.14%. 

Uterine weights in the oxamyl treated groups were comparable to controls. The mean blotted 

vehicle control uterine weight was 0.032% of the mean vehicle control terminal body weight. As 

expected, the absolute wet and blotted uterus weights for the positive control (EE) group were 

increased (p<0.05) by 3.1- and 2.4-fold, respectively. 

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The dose levels selected for this study are adequate based on marked decreases in brain and red 

blood cell cholinesterase activity at doses ≥0.75 mg/kg/day in studies in the database. 

No statistically significant changes were seen in uterine weight in this assay. Oxamyl is negative 

in the uterotrophic assay. 

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APPENDIX 2. Other Scientifically Relevant Information (OSRI) 

Published literature and Part 158 general toxicity studies considered relevant for determining the 

potential interaction of oxamyl with the endocrine system are summarized below. Given the 

breadth of toxicity data available on oxamyl, the only Part 158 studies discussed in this appendix 

are those that fulfill current guideline requirements and are directly relevant to assessing 

potential endocrine effects (i.e., multiple-generation rodent reproductive studies, development 

studies, chronic toxicity studies, etc.). 

Prenatal Development in Rodents (Rat) 

In a developmental toxicity study (MRID 40859201 and 44737501), oxamyl (97.2% purity) was 

administered by gavage to groups of pregnant CD BR rats (25/dose) at doses of 0, 0.2, 0.5, 0.8, 

and 1.5 mg/kg/day from GD 7 to 16, inclusive. On GD 22, the livers and gravid uteri were 

removed, and the dams were sacrificed. There were no mortalities, but clinical signs were 

increased (p<0.05) including diarrhea (6/25), eye discharge (12/25), salivation (20/25), tremors 

(25/25), and wet legs, perineal, and underbody (5–11/25) during the treatment period in the highdose animals, with a lower incidence (NS) of tremors at the medium-high dose (4/25), associated 

with ChE inhibition. While there were no significant dose-related changes in body weight or 

overall body weight gain, dams 17–30% less weight during GD 7–17 at ≥0.8 mg/kg/day. 

Decreases in food consumption were noted between GD 7 and 17 in the medium-high- (10%) 

and high-dose (16%) animals. Treatment had no effect on the reproductive parameters and/or 

fetal malformations, or visceral/skeletal variations. A dose-related decrease (p≤0.05) in fetal 

body weights was observed at the medium-low dose and above (↓3.9, 6.8, and 6.9%, 

respectively). The maternal toxicity NOAEL is 0.5 mg/kg/day, and the LOAEL is 0.8 mg/kg/day, 

based on decreased body weight gain, decreased food consumption, and the increased incidence 

of tremors. The developmental toxicity NOAEL is 0.2 mg/kg/day, and the LOAEL is 

0.5 mg/kg/day, based on dose-related decreases in fetal body weight. 

Prenatal Development in Non-Rodents (Rabbit) 

In a developmental toxicity study (MRID 00063009), pregnant New Zealand White rabbits 

(17/dose) were administered oxamyl (97.1% purity) by gavage at doses of 0, 1, 2, or 4 mg/kg/day 

on GD 6 to 19, inclusive. Ovulation was induced by i.v. injection of HCG (100 IU), followed by 

artificial insemination (GD 0). On GD 29, all surviving does were sacrificed and all fetuses were 

weighed, measured for crown-rump distance, and examined for external malformation/variations. 

Each fetus was examined viscerally by fresh dissection and the sex determined. The heads from 

one-third of the fetuses were removed, fixed in Bouin’s solution, and sectioned by Wilson’s 

freehand razor technique. All carcasses were eviscerated and processed for skeletal examination. 

One doe each in the low- and high-dose groups died prior to scheduled sacrifice; these deaths 

were attributed to gavage error. All other animals survived to terminal sacrifice, and no 

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treatment-related clinical signs of toxicity were observed in any treated group. Maternal absolute 

body weights and food consumption were comparable between the treated and control groups 

throughout the study; however, during the treatment interval (GD 6 to 19), the medium- and 

high-dose groups had decreased (p<0.05) body weight gains compared to control (↓61.5 and 

67.2%, respectively). Slight decreases (NS) in ovarian and uterine weights were noted in the 

medium- and high-dose groups, but data were not included. Therefore, the maternal toxicity 

LOAEL was 2 mg/kg/day based on reduced body weight gain, and the maternal toxicity NOAEL 

is 1 mg/kg/day. 

No treatment-related differences were observed between the treated and control groups for 

number of corpora luteal/doe, implantations/doe, pre-implantation loss, fetal body weights and 

lengths, or fetal sex ratios. Dose-related increased resorption rates for the medium- and highdose groups resulted in increased (NS) post-implantation losses and decreased (NS) litter sizes. 

For the control, low-, medium-, and high-dose groups, the post-implantation losses were 10.4%, 

8.7%, 15.9%, and 24.8%, respectively, and the number of live fetuses/litter was 6.6, 6.6, 5.9, and 

5.8. In the high-dose group only early resorptions were observed, and two animals had whole 

litter resorption consisting of early resorptions of 1 and 7 implantation sites, respectively. These 

were not considered treatment-related because a complete resorption in the rabbit is not 

uncommon. Furthermore, resorptions in the high-dose group may have been a consequence of 

the maternal toxicity at this dose. No treatment-related external, visceral, or skeletal 

malformations/variations were observed in the fetuses. Therefore, the developmental toxicity 

NOAEL was 4 mg/kg/day and a developmental LOAEL was not determined. 

Multi-Generation Reproduction in Rodents (Rat) 

In a two-generation reproduction study (MRID 41660801), Crl:CD®BR rats (30/sex/dose) were 

fed oxamyl (97.1 % purity) in the diet at nominal dosages of 0, 25, 75, or 150 ppm 

(approximately 0, 1.7, 5.2, or 11.6 mg/kg/day for males and 0, 2.0, 6.6, or 15.8 mg/kg/day for 

females, respectively). After 74 days of oxamyl dietary treatment, the F0 females were mated 

with males from the same group in a ratio of 1:1 until evidence of mating was obtained, or for a 

maximum of three weeks. The day on which mating was confirmed was designated GD 0. The F1

animals were mated in a similar fashion after 105 days (post-weaning) on the test diet. Study 

measurements included body weight/body weight gain, food consumption, and determination of 

reproductive parameters, organ weight (testes), and gross and microscopic pathology (including 

pituitary, testes, epididymis, prostate, seminal vesicles, coagulating gland, ovary, uterus, and 

vagina). 

No treatment-related mortality was observed; deaths of one high-dose female (F0) and three 

high-dose males (F1) were not considered due to treatment. Increased incidences of several 

clinical signs were observed in high-dose animals in each generation: F0 males, skin sores 

(p<0.05); F0 females, alopecia and stained fur (NS); F1 males, hyperactivity and skin sores 

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(p<0.05 and NS, respectively); F1 females, alopecia (also seen at the medium dose), 

hyperactivity, and skin sores (p<0.05, NS, and NS, respectively). 

Treatment-related decreases (p<0.05) in body weight were observed for both sexes in the 

medium- and high-dose groups during the premating phase, as well as during gestation and 

lactation phases in females. In the F0 generation, body weight for males and females was 

decreased at the medium (↓5 to 9%) and high doses (↓10 to 18% for males and ↓10 to 12% for 

females) during the premating phase (70 days of treated diet). In the F1 generation, body weight 

for males and females was decreased at the medium (↓7 to 20%) and high doses (↓17 to 37%) 

during the premating phase (105 days post-weaning on treated diet). Body weights were also 

decreased consistently during the gestation phase for the F0 females at the medium (↓6 to 8%) 

and high doses (↓13 to 15%) and for F1 females at the medium (↓12 to 13%) and high doses (↓19 

to 20%). Body weights recovered somewhat during the lactation phase with decreases for F0

females at the medium (↓2 to 8%) and high doses (↓7 to 15%) and F1 females at the medium (↓8 

to 12%) and high doses (↓15 to 21%). Similar decreases were noted for food consumption for 

high-dose animals and medium-dose males at a majority of the sampling intervals; food 

consumption was generally comparable to control for medium-dose females. 

No treatment-related effect was noted on absolute testes weights, but relative testes weights were 

increased (p<0.05) in high-dose F0 males (↑19%) and medium- and high-dose F1 males (↑12 and 

33%); however, these weight increases were not associated with any microscopic finding. In 

addition, no treatment-related microscopic findings were noted in F0 or F1 adults in the pituitary, 

epididymis, prostate, seminal vesicles, coagulating gland, ovary, uterus, or vagina. 

Based on clinical signs, and decreased body weights and food consumption, the LOAEL is 

75 ppm (approximately 5.2 and 6.6 mg/kg/day for males and females, respectively), and the 

NOAEL for systemic/developmental toxicity is 25 ppm (approximately 1.7 and 2.0 mg/kg/day 

for males and females, respectively). 

Fertility, mating, and gestational indices were not affected by oxamyl treatment at any dose in 

either generation. Therefore, the reproductive NOAEL is 150 ppm (approximately 11.6 and 

15.8 mg/kg/day for males and females, respectively). Offspring toxicity was observed in the 

medium- and high-dose groups in both generations based on significantly decreased pup body 

weights during lactation in both generations; in the F0 generation, pup body weights were 

decreased at the medium (↓7 to 14%) and high doses (↓13 to 25%), and decreased in the F1

generation at the medium (↓16 and 19%) and high doses (↓20 to 32%). In addition, at the high 

dose, the number of live pups per litter was generally decreased in both generations and the 

viability index was decreased 21 and 43%, respectively. Based on these results, the NOAEL for 

offspring toxicity is 25 ppm (approximately 1.7 and 2.0 mg/kg/day for males and females, 

respectively), and the LOAEL is 75 ppm (approximately 5.2 and 6.6 mg/kg/day for males and 

females, respectively) based on decreased pup body weights during lactation. 

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Chronic Oral Toxicity/Carcinogenicity in Rodents (Rat) 

In a combined chronic toxicity/carcinogenicity study (MRID 41963101) oxamyl (97.1%. purity) 

was administered in the diet to Crl:CD®BR rats (62 rats/sex/dose) at nominal doses of 0, 25, 50, 

100 or 150 ppm (mean-measured intake of oxamyl was calculated as 0, 0.992, 1.97, 4.19, or 6.99 

mg/kg/day for males and 0, 1.32, 2.69, 6.73 or 11.1 mg/kg/day for females, respectively) for two 

years. An interim sacrifice of 10 rats/sex/dose was conducted at 12 months. Body weight, food 

consumption, food efficiency, hematology, clinical chemistry, urinalysis, and organ weights 

were recorded. Plasma and RBC ChE activity was assessed at 1, 3, 6, 12, 18, and 24 months. 

After 104 weeks, all surviving rats in all groups were sacrificed for gross and histopathological 

evaluation. Select organs weighed at each sacrifice interval included liver, kidneys, testes, and 

ovaries. Brains were collected at the interim and final sacrifices for assessment of brain ChE 

activity. Gross and microscopic pathological examination included the liver, kidney, pituitary, 

thyroid/parathyroids, adrenals, mammary gland, testes, epididymides, prostate, seminal vesicles, 

uterus, vagina, and ovaries. 

Treatment with oxamyl did not affect mortality, food consumption, food efficiency, or 

hematology, clinical chemistry, and urinalysis parameters. The incidence of hyperactivity was 

increased (p<0.05) in the medium-high and high-dose groups (males/females, 52%/50% and 

63%/73%, respectively; control, 27%/17%). The incidence of swollen legs/paws in mid- and 

high-dose males was increased (p<0.05) by 29% and 34%, respectively, compared to 11% in 

control; in high-dose females, the incidence was increased (p<0.05) 23% compared to 5% in 

control. Females also exhibited an increased (p<0.05) incidence of skin sores or scabs in the 

medium-high and high-dose groups (61% and 82%, respectively) compared to 39% in control. 

Survival rates in treated males and females were similar to better than in control animals. Mean 

body weights and body weight gains were decreased in males and females at the medium-high 

and high doses during the first year of study. Body weights were decreased (p<0.05) in males at 

the medium-high (Day 7–470) and high doses (Day 7–680), and in females in the medium-highand high-dose groups throughout the study (Day 7–722); decreases were consistently >10% in 

the high-dose animals and >10% in the medium-high females by Day 84 until study termination. 

Body weight in medium-high dose males was >10% during a portion of the first year, but later 

decreases ranged from 7–9% through to Day 470. During the first year, the mean body weight 

gains in medium-high- and high-dose males were decreased 10% and 25% (p<0.05), 

respectively, compared to control, and medium-high- and high-dose female body weight gains 

were decreased by 27% and 37%, respectively. Although weekly body weights generally 

remained decreased (p<0.05) during the second year of the study, the overall body weight gain 

during this period was not significantly decreased. The decreased body weights and body weight 

gains in males and females were considered secondary to hyperactivity, since neither food 

consumption nor food efficiency (only slight decreases) was affected in these test groups. In 

medium-high- and high-dose males, plasma ChE activities were decreased (p<0.05) by 4 to 37% 

and 18 to 48%, respectively, during the study, compared to control. In medium-high- and highPage 49 of 56
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dose females, plasma ChE was inhibited (p<0.05) by 38% and 69%, respectively, after the first 

month of treatment only. Plasma ChE activity in males and females was not affected in the lower 

dose groups, and RBC and brain ChE activities were not decreased in treated animals. No 

histopathological findings were noted in the evaluated tissues, and a treatment-related increase in 

tumor incidence was not observed in this study. 

Based on the results of this study (body weights, hyperactivity, plasma ChE inhibition, and eye 

lesions), the highest dose tested (150 ppm) appeared to be a MTD, and was sufficiently high to 

evaluate the chronic toxicity and carcinogenicity of oxamyl. The systemic toxicity NOAEL is 

50 ppm (1.97 mg/kg/day for males and 2.69 mg/kg/day for females), and the LOAEL is 100 ppm 

(4.19 mg/kg/day for males and 6.73 mg/kg/day for females) based on hyperactivity, swollen 

legs/paws, and skin sores, decreased body weights and body weight gains, and inhibition of 

plasma ChE activity in male rats. 

Carcinogenicity in Rodents (Mouse) 

In a carcinogenicity study (MRID 00076813), CD-1 mice were administered oxamyl (97.1% 

purity) at nominal concentrations in the diet of 0, 25, 50, and 100 ppm for 24 months (calculated 

equivalency of 0, 3.75, 7.5 or 15/11.25 mg/kg/day). Initially, 80 mice/sex were included in each 

group, but extra mice were added to most treatment groups due to initial high mortality. The high 

dose was reduced to 75 ppm at Week 6 and extra mice were added to the treatment groups as 

follows: low-dose females and mid-dose males, n=81; mid-dose females, n=84; and high-dose 

animals, n=88. Mortality, clinical signs of toxicity, body weights and food consumption were 

monitored at appropriate times during the study. After 24 months, surviving mice in all groups 

were sacrificed for gross and histopathological evaluation. Select organs were weighed at 

terminal sacrifice (liver, kidneys, testes and heart; unknown if additional organ weights were 

determined). Gross and microscopic pathological examination included the liver, kidney, 

pituitary, thyroid, adrenals, mammary gland, testes, epididymides, prostate, seminal vesicles, 

uterus, and ovaries. 

Mortality was increased early in the study (2 males, 9 females at the medium dose, and 14 males 

and 11 females at the high dose through Week 4). Due to these high mortality rates, the dose for 

the high-dose group was decreased at Week 6 from 100 to 75 ppm. Overall survival at study 

termination was not significantly different for any treatment group compared to control. 

Apparent treatment-related effects on body weight were observed in this study in the mediumand high-dose groups. It was reported that decreased body weight was sporadic in females, but 

persistent in males, throughout the study. At Week 11, the male body weight was decreased by 

5%; no other body weight data was included in the Agency review. No treatment-related effect 

on food consumption was noted. Clinical chemistry assessment was not required or conducted, 

so ChE activity was not determined. 

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Decreases in liver weights in the medium- and high-dose males (↓23 and 16%, respectively) 

were not significant or dose-dependent. Similarly, increases (NS) in kidney weights in low- and 

high-dose males (↑6 and 9%, respectively) were not dose-dependent, and there was no change at 

the medium dose. No effects were noted in organ weights in female mice. No treatment-related 

gross pathological effects were noted. Apparent increases in glomerulosclerosis in all treated 

male mice, and pulmonary tumors in all treated females, were investigated against historical 

control data and determined to not be treatment-related. The NOAEL in the carcinogenicity 

study is 25 ppm (low dose; approximately 3.75 mg/kg/day), and the LOAEL is 50 ppm based on 

decreased body weight and increased mortality. 

Chronic Oral Toxicity/Carcinogenicity in Non-Rodents (Dog) 

In a one-year chronic feeding study (MRID 41697901) oxamyl (99% purity) was administered 

in the diet to groups of male and female beagle dogs (5/sex/dose) at nominal doses of 0, 50, 150, 

or 250 ppm (equivalent to 0, 1.56, 4.60, or 8.00 mg/kg/day for males and 0, 1.46, 4.50, or 7.84 

mg/kg/day for females, respectively). The dogs were offered the food once daily (approximately 

350 g/dog). Select organs were weighed at terminal sacrifice (liver, kidneys, 

thyroid/parathyroids, and testes). Gross and microscopic pathological examination included the 

liver, kidney, pituitary, thyroid/parathyroids, adrenals, mammary gland, testes, epididymides, 

prostate, vagina, uterus, and ovaries. ChE activity was determined in several brain sections (e.g., 

caudate nucleus, cerebellum/medulla, and cerebrum). 

One female dog in the high-dose group died on study, but the cause of death was not determined. 

Increased incidences of clinical signs including tremors and vomiting were observed in animals 

in the medium- and high-dose groups. Mean body weights/body weight gains in high-dose males 

and females were decreased 23%/81% and 17%/49%, respectively, at termination compared to 

control. Body weight decreases in males and females were ≥10% by Week 7, but decreases were 

only significant (p<0.05) for the last 7 weeks of the study (male body weight) and for male body 

weight gain. The body weight changes were concomitant with decreased food consumption and 

food efficiency. The food consumption/food efficiency in high-dose males was decreased 

(p<0.05) by 11%/75% compared to the control; in high-dose females, decreases of 7%/42% were 

NS. Administration of oxamyl did not produce any adverse effects in urinalysis, 

ophthalmological examinations, and gross pathology at any doses. In the low-dose males, plasma 

ChE was inhibited (p<0.05) at 6, 9, and 12 months by 33, 34, and 32%, respectively, compared 

to control; females exhibited minor decreases in plasma ChE at the same sampling times. Plasma 

ChE activity in the medium- and high-dose groups in males was decreased (p<0.05), but 

generally not dose-dependently, from Week 1 through study termination (approximately ↓50 to 

70%). Plasma ChE activity in the medium- and high-dose groups in females was decreased 

(p<0.05 or NS), but generally dose-dependently, from Week 1 through study termination 

(approximately ↓30 to 60%). Treatment-related effects were not noted for RBC, and brain ChE 

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activity was only decreased in the low-, medium-, and high-dose males; caudate nucleus: ↓31, 

47, and 30%, respectively, and cerebrum: ↓23, 46, and 34%. 

No treatment-related effects were noted for any absolute organ weights. Histologically, 3/5 highdose males exhibited increased regenerative renal tubular epithelial alterations. A NOAEL for 

male dogs was not established in this study due to decreased ChE activity in plasma and brain at 

all doses. 

Subsequently, a second one-year study (MRID 42052701) was repeated in male dogs (5/dose) at 

nominal oxamyl (98% purity) doses of 0, 12.5, 20, 35, or 50 ppm (equivalent to 0, 0.372, 0.577, 

0.930 or 1.36 mg/kg/day). The oxamyl exposure at the 50 ppm dose in this study was slightly 

lower than the exposure in the first study (1.56 mg/kg/day). In this study, food was offered 

ad libitum. All other study design parameters were similar to the previous chronic toxicity study 

in the dog. 

No treatment-related clinical signs were present in this study, and no mortality occurred. In 

addition, no treatment-related effects were observed on body weight, body weight gain, food 

consumption, clinical biochemistry/hematology, gross pathology, or organ weights. 

Histopathological examinations were not conducted for this study. At study termination, plasma 

ChE at the high dose was comparable to the control and RBC ChE activity was decreased 

(p<0.05, ↓22%), although RBC ChE activity throughout the study was variable. A decrease (NS, 

↓20%) in brain (cerebellum with medulla) ChE activity was noted in the high-dose group and is 

considered relevant, since tremors were observed at 150 and 250 ppm in males and at all doses in 

females in the previous study. In the medium-high dose group, plasma, RBC, and brain ChE 

activities were decreased 18%, 5%, and 2%, and may be considered a true NOAEL. Although 

the study was not replicated identically to the previous study in order to establish a NOAEL in 

male dogs, the results suggest that the plasma ChE activities are comparable and the information 

from this study can be utilized to derive a NOAEL in male dogs. 

The systemic toxicity NOAEL is 50 ppm (1.56 mg/kg/day for males and 1.46 mg/kg/day for 

females) and the LOAEL is 150 ppm (4.60 mg/kg/day for males and 4.50 mg/kg/day for 

females), based on decreased body weights and body weight gains. The ChE NOAEL is 35 ppm 

(0.930 mg/kg/day for males) and 50 ppm (1.56 mg/kg/day for females), and LOAEL is 50 ppm 

(1.36 mg/kg/day for males and 4.50 mg/kg/day for females), based on brain ChE activities in 

males and vomiting, tremors, and plasma and brain ChE inhibition in females. 

Avian Reproduction (Duck) (OCSPP 850.2300) 

In an avian reproduction study (MRID 00116609), wild-caught young adult Mallard ducks 

(Anas platyrhynchos) approaching their first laying season were administered oxamyl (97.1% 

purity) in the feed at concentrations of 0 (control), 10, or 50 ppm for 22 weeks (ten weeks prior 

to the start of egg production and during twelve weeks of egg production). Each treatment group 

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comprised six replicates, with two drakes and five hens per pen. A progressive photoperiod was 

employed in this study: 7 hours/day from Day 1 to 44; 8 hours/day from Day 45 to 51; 

9 hours/day from Day 52 to 65; 12 hours/day from Day 66 to 72; 13 hours/day from Day 73 to 

79; and 14 hours/day from Day 80 to 154. Temperature ranged from 8 to 24°C throughout the 

study; humidity was not reported. Individual adult body weights were recorded on Days 0, 14, 

28, 42, 56, and 154; food consumption in each replicate was measured weekly throughout the 

pre-treatment and treatment periods of the adult phase. Individual chick body weights were 

recorded within 24 hours of hatching and on Day 14 after hatching; egg shell thickness was 

measured on the first two days of Weeks 1, 3, 5, 7, 9, and 11 of the egg production period. Adult 

birds and chicks were observed daily for mortality and clinical signs; all adult birds were 

subjected to post-mortem examination. ChE determinations were not conducted. 

Seven birds died or were sacrificed during the pre-egg production period primarily attributed to 

pen-mate aggression (two in the low-dose and five in the high-dose groups), all of which were 

replaced with spare birds. During the egg production period, six birds died in the control group 

(14%), two birds died in the low-dose group (5%), and nine birds died in the high-dose group 

(21%) (one was sacrificed). Pen-mate aggression (bullying) continued during the egg production 

period (Days 71–154) and was listed as an observation in five of the 14 birds that died during the 

study. Post mortem examination showed that a number of females were not in egg production at 

the end of the 12-week laying period as their ovaries were underdeveloped. According to the 

reviewer’s report, the study indicated a slight effect on egg production at 50 ppm and a 

potentially higher chance of infertility in the eggs. Although there were no treatment-related 

effects on adult mortality, food consumption, or body weight, there is concern with the ability to 

discern endocrine-related effects seen in the mallard study due to the presence of mortality and 

aggressive behavior in the pens. 

In another avian reproduction study (MRID 00116610), young adult Bobwhite quail (Colinus 

virginianus), were offered diet containing technical oxamyl (97.1% purity) at concentrations of 

0, 10, or 50 ppm diet for 28 weeks (sixteen weeks prior to the start of egg production and twelve 

weeks during egg production). Each treatment group was comprised of 14 replicates of one male 

and two females. Individual adult body weights were recorded on Days 0, 14, 28, 42, 56, 70, 84, 

and 196; food consumption in each replicate was measured weekly throughout the pre-treatment 

and treatment periods of the adult phase. Individual chick body weights were recorded within, 24 

hours of hatching and on Day 14 after hatching; egg shell thickness was measured on the first 

two days of Weeks 1, 3, 5, 7, 9, and 11 of the egg-production period. Adult birds and chicks 

were observed daily for mortality and clinical signs; all adult birds were subjected to postmortem examination. ChE determinations were not conducted during this study. 

Four birds died or were sacrificed (two in the control group and two in the high-dose group) 

during the pre-egg production period; all were replaced with spare birds. There was no 

treatment-related effect on adult mortality; clinical observations and post mortem changes were 

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Page 46 of 48 

consistent with long-term housing of birds in cages, and were not related to treatment. Adult 

body weight changes over the treatment period were similar in all groups, and there was no 

evidence of a treatment-related effect. Adult food consumption was decreased (significance NR) 

in the two oxamyl-treated groups during both pre-egg production and egg production periods 

(data NR). Initial chick body weights were similar overall in all treatment groups; chicks that 

died after hatching during the 14-day observation period were examined and no abnormalities 

were detected. Of the reproductive parameters measured, few differences were detected between 

the control and treatment groups, with two exceptions: the proportion of damaged eggs was 

lower in the low-dose group compared to control (15 vs. 28 control), and the proportion of chicks 

surviving to 14 days was significantly higher in the 10 ppm diet treatment compared to control 

(Williams test, p<0.05; 79.5 vs. 80.1%). 

The reproductive NOAEC for bobwhite quail exposed to oxamyl in the diet for 28 weeks was 

50 ppm diet, based on the absence of adverse reproductive effects at the highest dose tested. 

Fish Early Life-Stage Toxicity; (OCSPP 850.1400) 

In a freshwater fish early life-stage toxicity test (MRIDs 40901101 and 41472301), Rainbow 

trout (Salmo gairdnerii, (Oncorhynchus mykiss)) embryos and larvae were continuously 

exposed to oxamyl (97.2% purity) at nominal concentrations of 0 (water control), 0.06, 0.12, 

0.25, 0.50, 1.0, and 2.0 mg/L (mean-measured concentrations of 0.06, 0.10, 0.23, 0.40, 0.77, 

and 1.5 mg/L) in a flow-through system for 61 days. Observations were made on embryo 

hatching and larval survival and growth. Twenty embryos were added to each cup 

(80 embryos/concentration). The first larvae hatched on Day 20 and hatching was considered 

complete by Day 29. As the larvae hatched, they were transferred from the embryo cup to the 

appropriate aquarium, with up to 15 larvae per replicate; excess larvae were counted and then 

discarded. Survival of the remaining larvae was assessed for 32 days, and at the end of the study 

all surviving larvae were weighed and measured.

The mean measured concentrations of oxamyl in the test vessels ranged from 75% to 100% of 

the nominal values. No treatment-related effects on embryo hatching, larval survival, first day of 

larval swim-up, or larval growth was observed at measured test concentrations of 0.06 to 

0.77 mg/L. At 1.5 mg/L (highest concentration tested), delays (p<0.05) in the first day of embryo 

hatching and larval swim-up were observed compared to control, as well as a decrease (↓96%; 

p<0.05) in the percentage hatching. The NOAEC for rainbow trout exposed to oxamyl was 

0.77 mg/L, based on effects on embryo hatching and larval swim-up at the high dose (1.5 mg/L).

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APPENDIX 3: References Not Utilized in the Oxamyl WoE Analysis 

In 2009, after public review and comment, a final list of 67 chemicals and schedule for issuing 

Test Orders for the EDSP Tier 1 screening battery was made available in a Federal Register 

Notice issued October 21, 2009 (74 FR 54422). The agency’s review of the initial data submitted 

as “other scientifically relevant information (OSRI) was provided in the Report of the Endocrine 

Disruptor Review Team (USEPA, 2010). 

Beginning in 2011, the agency has reviewed data cited as “OSRI which included Part 158 studies 

previously submitted to the agency for registration/reregistration, published literature articles 

and/or Tier 1 assays. The agency also conducted a more recent search (2009 to 2014) of 

available scientific literature for any additional relevant information for their weight of evidence 

(WoE) evaluations. These articles were evaluated in accordance with the agencies Evaluation 

Guidelines for Ecological Toxicity Data in Open Literature, May 2011 

(http://www.epa.gov/pesticides/science/efed/policy_guidance/team_authors/endangered_species

_reregistration_workgroup/PDF_rot/esa_evaluation_open_literature.pdf) and the 2012 Guidance 

for considering and Using Open Literature Toxicity Studies to Support Human Health Risk 

Assessment (http://www.epa.gov/pesticides/science/lit-studies.pdf). 

The following published and unpublished references were considered for use in the WoE 

analysis for Oxamyl but were not utilized due to one or more of the following reasons: 1) the 

article was not available in English; 2) the compound of interest was not used in the study; 3) the 

test material was not adequately described; 4) a formulated end-use product or mixture of 

chemicals was utilized as the test material; 5) only acute mortality toxicity data were provided; 

6) the experimental conditions were not adequately described; 7) only an abstract of the study 

was available; 8) the reference is a review article or book chapter and does not contain primary 

study data; 9) insufficient information was available to adequately assess the validity of the study 

results; 10) the 40 CFR Part 158 guideline study was classified as unacceptable/inadequate; 11) 

the study dealt only with non-EDSP assay development; 12) no specific endocrine-related 

endpoints were assessed in the study; and 13) the study contained only data on invertebrates. 

Andersen, H.R., Vinggaard, A.M., Rasmussen, T.H., Gjermandsen, I.M., and BonefeldJorgensen, E.C. (2002). Effects of Currently Used Pesticides in Assays for Estrogenicity, 

Androgenicity, and Aromatase Activity In Vitro. Toxicol. Appl. Pharmacol. 179:1–12. 

Grubbs, C.J., Perkham, J.C., and Cato, K.D. (1983). Mammary carcinogenesis in rats in relation 

to the age at time of N-nitroso-N-methylurea administration. J. Natl. Cancer Institute. 

70:209-212. 

Hellwig, J., van Ravenzwaay, B., Mayer, M., and Gembardt, C. (2000). Pre- and postnatal oral 

toxicity of vinclozolin in Wistar and Long-Evans rats. Regulatory Toxicology and Pharmacolgy.

32:42–50. 

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Hseuh, A.J.W., Dufau, M.L., and Catt, K.J. (1977). Gonadotrophin induced hormone receptors 

and desensitization of testicular 3',5'-cyclic AMP and testosterone responses. Proc. Natl. Acad. 

Sci. USA 74:592–595. 

Jiao, B., Yeung, E.K.C., Chan, C.B., and Cheng, C.H.K. (2008). Establishment of a Transgenic 

Yeast Screening System for Estrogenicity and Identification of the Anti-Estrogenic Activity of 

Malachite Green. J. Cell. Biochem. 105:1399–1409. 

Klotz, D. M., Arnold, S.F., and McLachlan, J.A. (1997). Inhibition of 17 Beta-Estradiol and 

Progesterone Activity in Human Breast Cancer and Endometrial Cancer Cells by Carbamate 

Insecticides. Life Sci. 60:1467–1475. 

Kojima, H., Katsura, E., Takeuchi, S., Niiyama, K., and Kobayashi, K. (2004). Screening for 

Estrogen and Androgen Receptor Activities in 200 Pesticides by In Vitro Reporter Gene Assays 

Using Chinese Hamster Ovary Cells. Environ. Health. Perspec. 112:524–531. 

Nendza, M. and Wenzel, A. (2006). Discriminating Toxicant Classes by Mode of Action, 1) 

(Eco)toxicity Profiles. Environ. Sci. & Pollut. Res. 13:192–203. 

Nishihara, T., Nishikawa, J., Kanayama, T., Dakeyama, F., Saito, K., Imagawa, M., Takatori, S., 

Kitagawa, Y., Hori, S., and Utsumi, H. (2000). Estrogenic activities of 517 chemicals by yeast 

two-hybrid assay. J. of Health Sci. 46: 282–298. 

Stevens, J.T., Tobia, A., Lamb, J. C., Tellone, C., and O'Neil, F. (1997). FIFRA Subdivision F 

testing guidelines: Are these tests adequate to detect potential hormonal activity for crop 

protection chemicals? J. Toxicol. Environ. Health 50:415–431. 

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