UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

Date: February 28, 2014 

OFFICE OF 

CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

SUBJECT: MCPP, MCPP-p (acid), MCPP-p DMAS, and MCPP-p potassium salt, 

Human Health Assessment Seeping Document in Support of Registration Review. 

PC Code: 03150 I, 3 1503, 031519, 031 520, 129046 and 19046 DP Barcode: D416761 

Decision No.: 485917 Registration No.: NA 

Petition Nos.: NA Regulatory Action: Registration Review 

Risk Assess Type: Scoping Document CAS.: 16484-77-8, 66423-09-4,66423-05-0, 7085-19-0 

TXR No.: NA. MRID No. : 44655702, 44655703 and 45033101 

FROM: ~L~ Seyed 

Linda Taylor

Tadayo, n

Ph

, Risk 

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l · ~ ~ ~c._ Peter Savoia, Chemist -0 

Risk Assessment Branch J~d VII ") 

THRU: 

Health Effects Division (7509P) 

Office of Pesticide Programs 

Michael. S. Metzger, Branch Chief/ J W. 

Rtsk Assessment Branch v and viHvf::.-4.. . Health Effects Division (7509P) "'--· 

Office of Pesticide Programs 

TO: Kaitlin Keller, Chemical Review Manager 

Pesticide Re-evaluation Division (7508P) 

Office of Pesticide Programs 

EXECUTIVE SUMMARY 

L{r- 1 

The HED Registration Review team has evaluated the most recent human health assessments and 

database for the herbicide Mecoprop. Current registrations ofMCPP and MCPP-p include the 

acid forms, dimethylamine salts, ethylhexyl esters, and potassium salts. At the present, the 

MCPP-p Task Force is supporting MCPP-p (acid), MCPP-p dimethylamine (MCPP-p DMS), 

and MCPP-p potassium. Mecoprop-p (MCPP-p) is a member ofthe chlorophenoxy class of 

herbicides. It is the enriched isomer form (R isomer) while mecoprop (MCPP) is a 50:50 racemic 

mixture of the dextro (R) and levo (S) isomers. 

Page 1 of21 
HED has considered the most recent human-health risk assessments for MCPP-p; updates to the 

toxicity, exposure, and usage databases; and current Agency science policy and risk assessment 

methodologies to determine the scope of work necessary to support Registration Review. In 

addition, HED conducted an open literature search to look for new literature relevant to the 

human health risk assessment. The results of the literature search showed that no new 

information relevant to the human health risk assessment has been published. 

MCPP-p is used in combination with other herbicides for postemergence broadleaf weed and 

brush control. It is used primarily on turf (i.e. lawns and golf courses) and sod farms with smaller 

quantities used on non-turf areas such as rights-of way. The commercial and agricultural 

products are generally formulated as liquids and granular formulations. The residential products 

are typically formulated as granular weed and feed formulations, liquid concentrates, or Readyto-Use sprays. One MCPP-p DMS residential product (EPA Reg. No. 228-190) is formulated as 

an aerosol spray can. There are no registered food uses or established or pending tolerances 

at this time. 

Toxicity/Hazard 

The toxicity database for mecoprop-p (MCPP-p) is incomplete. A 28-day inhalation toxicity 

study is required. All other toxicity data requirements are satisfied for MCPP-p when 

supplemented with the mecoprop (MCPP) database. Upon receipt of the MCPP-p inhalation 

study, HED will evaluate the toxicity database for characterization of potential developmental, 

reproductive, carcinogenetic, mutagenic, neurotoxic, and immunotoxic effects. 

Dietary Exposure 

Since MCPP-p products are used outdoors on turf and for woody plant control in non-crop areas, 

the dietary risk assessment considers only drinking water exposures (no food use). In the most 

recent risk assessment, acute and chronic risks were below the HED level of concern (0341965; 

07/26/2007). Updated dietary exposure assessments for MCPP-p may be necessary to consider 

the most recent drinking water consumption data, and to include newly estimated drinking water 

concentrations. In addition, if new points of departures are selected a revised dietary assessment 

may be needed. 

Residential Exposure 

The residential exposure database is adequate to support registration review for MCPP-p. In the 

last risk assessment (D341965; 07/26/2007), the calculated risk did not exceed the level of 

concern (MOE> 1 00). Residential handler scenarios may need to be updated in the registration 

review assessment, reflecting any updated doses and endpoints for risk assessment, HED's 

Residential SOPs, and current policies. 

Previous residential post-application assessments, which assessed incidental oral exposures only, 

relied on default assumptions for turf transferrable residues following treatments. Chemicalspecific TTR data are not required to assess exposure to residues following MCPP-p treatments. 

For the residential postapplication assessment, incidental oral exposures will be updated in the 

registration review assessment, reflecting any updated doses and endpoints for risk assessment, 

HED's Residential SOPs, and current policies. 

Page 2 of21 
Page 3 of 21

Aggregate Assessment

In the most recent risk assessment, HED provided updated aggregate exposure and risk estimates 

for drinking water and residential exposures. The exposure scenarios aggregated are: chronic 

drinking water with short-term incidental oral ingestions in infants and children; and chronic 

drinking water with short-term inhalation of adult residential handlers. The combined MOE’s for 

the scenarios examined were below HED’s level of concern (i.e. MOE > 100). Aggregate 

exposures of MCPP-p will be revised during registration review to consider new dietary and 

residential exposures estimates. 

Occupational Exposure

The occupational exposure database is adequate to support registration review for MCPP-p. No 

dermal hazard has been identified for MCPP-p for short- or intermediate-term exposure 

scenarios; therefore, post-application exposure and risks were not quantified for those exposure 

durations. Long-term dermal exposure to MCPP-p is unlikely due to the use pattern of MCPP-p, 

typically applied once or twice per season. The MOEs for occupational handler exposures were 

calculated for short/intermediate term inhalation exposures using standard assumptions and unit 

exposure data. In the last risk assessment (D341965; 07/26/2007), the calculated occupational 

handler risk did not exceed the level of concern (MOE>100). Updated occupational handler 

assessments may be required during registration review reflecting any updated exposure 

methodology and endpoints for risk assessment. In addition, the handheld equipment 

applications to turf scenarios need to be updated during registration review. 

1.0 FORMULATIONS AND USE PATTERNS 

HED used the OPPIN data base to identify all uses of the MCPP-p forms and the number of 

associated end use product labels. The acid and dimethylamine (DMA) forms have the most 

products. The commercial products are generally formulated as liquids and standard granules. 

Two acid products (2217-784 and 2217-814) are wettable powders and are labeled for 

professional applicator use on turf. The residential products are typically formulated as granular 

weed and feed formulations or as liquids in concentrates or Ready-to-Use sprays. One

dimethylamine (DMA) residential product (228-190) is formulated as an aerosol spray can. 

MCPP-p is used in combination with other herbicides for postemergence broadleaf weed and 

brush control. It is used primarily on turf (i.e. lawns and golf courses) and sod farms with smaller 

quantities used on non-turf areas such as rights-of way. There are no registered food uses or

established or pending tolerances at this time.

Agricultural Uses

None.

Non-Agricultural and Residential Uses

MCPP-p is registered for use on lawns, recreational turf, sports fields, sod farms, roadsides, and

rights-of-way. 
Page 4 of 21

2.0 HAZARD IDENTIFICATION/TOXICOLOGY

Hazard Identification/Toxicology

MCPP-p is a member of the chlorophenoxy class of herbicides that function by mimicking the 

action of auxins, plant growth hormones. 

The toxicity database for mecoprop-p (MCPP-p) is incomplete. A 28-day inhalation toxicity 

study is required. All other toxicity data requirements are satisfied for MCPP-p when 

supplemented with the mecoprop (MCPP) database. Upon receipt of the MCPP-p inhalation 

study, HED will evaluate the toxicity database for characterization of potential developmental, 

reproductive, carcinogenetic, mutagenic, neurotoxic, and immunotoxic effects. 

MCPP-p is the enriched isomer form (R isomer), whereas MCPP is a 50:50 racemic mixture of 

dextro (R) and levo (L) isomers. MCPP-p (acid) is reported to be the more herbicidally-active 

compound. In metabolism studies in rats, MCPP-p and the ester (MCPP-p-2-EHE) and amine 

salt (MCPP-p-DMA) forms were rapidly absorbed and eliminated mainly in the urine; no 

bioaccumulation occurred. For each compound, the major metabolite is MCPP-OH. 

The major target organs are the kidney and liver. Kidney toxicity is manifested as increased 

kidney weight (rats and mice) and chronic nephropathy in mice. Liver toxicity is manifested as 

increased liver weights, increased liver enzymes, and microscopic changes in rats and mice. The 

effects are consistent across time and species and do not appear to progress over time. Although 

absorption and distribution of chlorophenoxy herbicides and other organic acids are similar 

across all mammalian species evaluated, the decreased capacity of the dog to eliminate organic 

acids results in higher blood levels and a longer elimination half-life relative to those found in 

the rat and other mammalian species. Consequently, effects are seen at lower dose levels in the 

dog than in the rat. Because of this difference and because human metabolism is more similar to 

rats than dogs, the rat is a better predictor of the potential toxicity of MCPP-p in humans than the 

dog, and doses and endpoints from rat studies were used in all MCPP-p risk assessments. 

Developmental toxicity was not observed in the rabbit following exposure to MCPP-p and 

MCPP. Developmental toxicity was observed in the rat at the same dose level where maternal 

toxicity was observed following exposure to MCPP-p but in the absence of maternal toxicity 

following exposure to MCPP. Reproductive toxicity was not observed in the rat in the MCPP-p 

1-generation reproduction study. The main effect in the reproduction study was decreased 

implantations resulting in a decreased number of pups born and a decrease in male pup body 

weight at weaning at a dose that also caused maternal toxicity (decreased body weight). The 

acute neurotoxicity study results indicated that MCPP-p produced changes in functional 

observation battery (FOB) parameters (closed eye lids, prone body position, hypoactivity), 

ataxia, increased foot splay, and decreased motor activity. However, no neurotoxic effects were 

seen in the subchronic neurotoxicity study with MCPP-p. Histopathological changes were not 

found in either of the neurotoxicity studies. 
Page 5 of 21

MCPP-p is classified as “suggestive of carcinogenicity, but not sufficient to assess human 

carcinogenic potential” by the oral route of exposure. This is based on the occurrence of liver 

tumors in one sex (female) of a single species (mouse) following exposure to MCPP-p; there is 

no treatment-related increase in tumor incidence in rats of either sex following exposure to 

MCPP. Additionally, MCPP-p was not found to be mutagenic in either bacteria or cultured cells. 

There is no concern for immunotoxicity. MCPP-p is not acutely toxic by the oral, dermal, and 

inhalation routes of exposure based on lethality studies. It is a severe eye irritant but not a 

dermal irritant or dermal sensitizer. 

The HASPOC determined that a 28-day inhalation toxicity study is required to better estimate 

risk for occupational inhalation exposure due to the potential for repeated inhalation exposure to 

aerosolized formulations of MCPP-p, and based on the portal-of-entry findings observed in the 

inhalation studies on other chlorophenoxy compounds, (TXR No. 0056865, dated 1/7/14). 

An immunotoxicity study, which is required in accordance with new data requirements for 

conventional pesticide registration (40 CFR Part 158) has not been submitted for MCPP-p. The 

HASPOC determined that the immunotoxicity study for MCPP-p is not required since the target 

organs of MCPP-p are the kidneys and liver; the toxicity profile provides no indication of 

toxicity to the immune system; and the PODs selected for overall risk assessments is based on 

the most sensitive endpoints and will be protective of any potential immunotoxicity TXR No. 

0056865, dated 1/7/14). 

The acute and subchronic/chronic toxicity profile tables for MCPP, MCPP-p, MCPP-p-DMA, 

and MCPP-p-2-EHE are included in APPENDIX A, Attachment 1. Toxicity endpoints, PODs, 

and UF/SFs were selected for oral and inhalation exposure pathways for the Human Health Risk 

Assessment conducted in 2007 (D341965), and these are presented in Attachment 2 (Table A2.1 

and Table A2.2). 

Upon receipt and review of the outstanding toxicology data and consideration of all available 

data, the endpoints for the inhalation risk assessment and all uncertainty factors will be reevaluated during registration review to reflect updated data and uncertainty factor policies, and a 

new risk assessment done, if necessary. 

Conclusions: The toxicity data base for MCPP-p is considered incomplete. A repeat dose 

inhalation toxicity study is required. All other toxicity data requirements are satisfied for MCPPp. Once the inhalation toxicity study has been received and reviewed and considered in light of 

current policies and procedures, its’ impact on the endpoints, PODs, and UF/SFs for the 

inhalation exposure risk assessments will be considered during registration review.

3.0 DIETARY EXPOSURE

There is no registered food or feed uses for MCPP-p products, and thus no food-related dietary 

risk assessments were conducted. However, since MCPP-p -p products are used outdoors on turf 

(golf courses, lawns, parks, etc.) and for woody plant control in non-crop areas (utility rights-ofway), the risk assessment considers drinking water exposures. In the most recent assessment (J. 

Hetrick, 6/26/2006, D322772), ground water residues were low in comparison to surface water. 
Page 6 of 21

The conservative screening-level drinking water assessment for surface water predicted acute 

and chronic EDWCs using the Tier II PRZM-EXAMS - Index Reservoir model for uses on turf, 

the use resulting in the highest EDWCs. Acute and chronic dietary exposure estimates were 

below the HED level of concern (i.e. < 100% of the acute and chronic population adjusted dose) 

for the general population and all population subgroups. 

Conclusions: Dietary exposure assessments for MCPP-p may be necessary to consider the most 

recent drinking water consumption data from the 2003-2008 U.S. Department of Agriculture’s

National Health and Nutrition Examination Survey, What We Eat in America (WWEA), and to

include newly estimated drinking water concentrations. In addition, if new endpoints are 

selected a revised dietary assessment may be needed. 

4.0 RESIDENTIAL EXPOSURE

Residental exposure to MCPP-p may occur from uses on turfgrass and golf courses. 

Residential Handler

Since MCPP-p, its salts, and esters are not restricted use pesticides, HED previously conducted a 

residential handler exposure assessment for lawn use (D341965; 07/26/2007). The scenarios 

assessed were: hand application of granules (spot treatment), belly grinder application (spot 

treatment), load/apply granules with a broadcast spreader, mix/load/apply with a hose-end 

sprayer (mix your own), mix/load/apply with a hose-end sprayer (ready to use), mix/load/apply 

with hand held Pump and mix/load/apply with ready to use sprayer. The inhalation MOE’s 

ranged from 190,000 to 9,900,000 and risk estimates were not of concern.

For residential handlers, the following exposure scenarios may need to be included in the 

registration review assessment for both broadcast and spot treatment of turf in accordance with 

the 2012 Residential SOPs (revised since the last assessment): 

 hand application of granules; belly grinder application; 

 load/apply granules with a broadcast spreader; 

 mix/load/apply with a hose-end sprayer (mix your own); 

 mix/load/apply with a hose-end sprayer (ready to use); 

 mix/load/apply with hand held pump sprayer and

 mix/load/apply with ready to use sprayer.

Residential Post Application 

There is potential for residential post-application exposure to registered turf uses. Exposure 

scenarios include contact with treated turf and playing golf on treated golf courses. Quantitative 

residential dermal post-application risk assessments were not conducted based on the absence of 

toxicity via the dermal route. However, an incidental oral exposure assessment for children was 

conducted in the most recent risk assessment (D341965; 07/26/2007). All of the short-term 

MOEs for these exposures were greater than 100, and thus are not of risk concern (MOE’s 

ranged from 1,900 to 580,000). Chemical-specific TTR data are available (MRID 44655702, 

44655703 and 45033101), and will be used to estimate dermal hand loading to calculate 

incidental oral exposure. Exposure and risk estimates will be assessed in registration review in 
Page 7 of 21

accordance with the revised 2012 Residential SOPs. Incidental oral exposure scenarios include 

hand-to-mouth; object-to-mouth; incidental soil ingestion; and episodic ingestion of granules.

Spray Drift

Residential exposures resulting from off-site transport (e.g., spray drift or volatilization) might 

occur as a result of applications of MCPP-p. The Agency is in the process of evaluating these 

types of exposures and might, as appropriate, develop policies and procedures to identify the 

need for and, subsequently, the way to incorporate these post-application exposures into the 

Agency’s risk assessments. The need for spray drift and volatilization risk assessment for 

MCPP-p will be examined during registration review.

Conclusions: Updated residential exposure assessments may be needed during registration 

review. Moreover, exposure and risk estimates may be assessed in accordance with the 2012 

Residential SOPs during registration review. As necessary, a post-application risk assessment 

may be conducted in accordance with the development of relevant HED policies for risk 

assessment (e.g., spray drift, or volatilization).

5.0 AGGREGATE EXPOSURE AND RISK ASSESSMENT

In accordance with the Food Quality Protection Act (FQPA), HED must consider and aggregate 

pesticide exposures and risks from three major sources: food, drinking water, and residential 

exposures. In the most recent risk assessment (D341965; 07/26/2007), the aggregate exposure 

and risk estimates included only exposure via drinking water and residential exposures through 

the inhalation and incidental oral routes because there are no food uses and a dermal exposure 

assessment is not required. Quantification of dermal risk is not required because there is no 

toxicity via the dermal route of exposure. 

Acute

It should be noted that individual acute assessments were performed for acute drinking water 

exposure and acute exposure for children resulting from consuming granules. Since there is little 

likelihood that these two scenarios would occur simultaneously, it is not appropriate to aggregate 

these two exposure and risks estimates. The acute aggregate assessment is based on acute 

dietary exposure only, in this case only exposure via drinking water as there is no registered food 

uses. The acute risk was not of concern.
Page 8 of 21

Chronic

The chronic aggregate assessment includes exposure via drinking water only since no chronic 

residential scenarios were identified. There was no chronic risk of concern for drinking water. 

Short-term

The exposure scenarios aggregated are chronic drinking water with short-term incidental oral 

ingestions in infants and children and chronic drinking water with short-term inhalation of adult 

residential handlers. The toxicity endpoints for short-term incidental oral and inhalation 

exposures were derived from a rat subchronic feeding/neurotoxicity study with a NOAEL of 35

mg/kg/day. The aggregate risk for residential handlers, and infants and children are obtained by

comparing this NOAEL to the sum of the exposure values to calculate the MOE and comparing 

the calculated MOE to the target MOE of 100. The aggregated MOE’s for the scenarios 

examined were below HED’s level of concern (i.e. MOE > 100). 

Based on the use pattern for MCPP-p on turf, there are no intermediate- or long-term residential 

exposure scenarios. 

Conclusions: Aggregate exposures of MCPP-p may be revised during registration review to 

consider new dietary and residential exposures estimates or changes in toxicological endpoints. 

6.0 OCCUPATIONAL EXPOSURE 

There is potential for occupational handler and post-application exposure from registered uses on 

recreational turf (golf course), sports fields, sod farms, roadsides, and rights-of-way. 

MCPP-p, its salts, and esters may be applied using aerial (sod farms only), groundboom, handheld spray, and granular spreader equipment. The personal protective equipment (PPE) required 

for handlers consists of a single layer of clothing (long sleeve shirt, long pants, and socks plus 

shoes) with no respirator. The Restricted Entry Interval for MCPP-p is 48 hours because it is a 

severe eye irritant (i.e. Toxicity Category I).

The occupational uses of MCPP-p, its salts, and esters result in short-term (1 - 30 days) and 

intermediate-term (1 - 6 months) occupational exposures. 

Occupational Handler Exposure

There is potential for occupational handler exposure during mixing/loading and applying.

Occupational handler scenarios were previously assessed (D341965; 07/26/2007). All short- and 

intermediate-term inhalation MOEs for agricultural handler scenarios were assessed at baseline 

PPE except for aerial applicators, who were assessed with closed cockpit (i.e., engineering 

controls) built in. All scenarios have MOEs above the target MOE of 100 (ranged from 445 to 

410,000) and thus are not a risk concern at baseline exposure.

Recommended unit exposures for occupational handler assessments have generally been derived 

only from the Pesticide Handlers Exposure Database (PHED). However, recently both the 

Outdoor Residential Exposure Task Force (ORETF) and the Agricultural Handler Exposure Task 

Force (AHETF) have produced pesticide handler exposure monitoring data that the Agency is 

using in place of PHED (http://www.epa.gov/pesticides/science/handler-exposure-data.html). As 
Page 9 of 21

more reliable data become available, the Agency will continue to replace existing data. Revised 

assessments which incorporate these new exposure monitoring data may be required during 

registration review.

Occupational Post-application Exposure

There is potential for occupational post-application exposure. In the absence of toxicity via the 

dermal route, no quantitative dermal post-application risk assessment is required for the 

occupational uses of MCPP-p, its salts, and esters. The REI of 48 hours is on registered labels

and is considered appropriate based on the toxicity of the technical ingredient. A quantitative 

dermal post-application risk assessment is not required due to the lack of toxicity via the dermal 

route. Since there is no use on agricultural crops, Dislodgeable Foliar Residue (DFR) is not 

required. 

Conclusions: Updated occupational handler exposure assessments may be needed during 

registration review if a new inhalation dose and endpoint for risk assessment are selected, and to 

consider the most current exposure data. 

7.0 PUBLIC HEALTH AND PESTICIDE EPIDEMIOLOGY DATA 

There are no incidents reported for MCPP as a single chemical only, but there is a high absolute 

number of incidents reported involving MCPP with another active ingredient (D417595,S 

Recore, 02/04/2014). Although vast majority of these incidents were of low severity, some high 

severity outcomes are reported in the IDS database. It is important to note that since most of 

these reported incidents involve more than one active ingredient (i.e. MCPP and another active 

ingredient), the incidents that were reported were not necessarily attributable to MCPP. Further, 

while incident information can be an important source of feedback to the Agency, reports of 

adverse health effects allegedly due to a specific pesticide exposure (i.e., an “incident”) are 

largely self-reported and therefore, generally speaking, neither exposure to a pesticide or 

reported symptom (or the connection between the two) is validated or otherwise confirmed. 

Typically, causation cannot be determined based on incident data. Nevertheless, based on the 

absolute number of incidents and the few high severity outcomes that are reported, these incident 

data may warrant further analysis in the preliminary risk assessment phase of Registration 

Review. Obtaining additional information on current usage data for MCPP would improve 

future assessments.

8.0 CUMULATIVE RISK ASSESSMENT 

Unlike other pesticides for which EPA has followed a cumulative risk approach based on a 

common mechanism of toxicity, EPA has not made a common mechanism of toxicity finding as 

to MCPP-p and any other substances and MCPP-p does not appear to produce a toxic metabolite 

produced by other substances. For the purposes of this risk assessment, therefore, EPA has not 

assumed that MCPP-p has a common mechanism of toxicity with other substances. For 

information regarding EPA’s efforts to determine which chemicals have a common mechanism 

of toxicity and to evaluate the cumulative effects of such chemicals, see the policy statements 

released by EPA’s Office of Pesticide Programs concerning common mechanism determinations 

and procedures for cumulating effects from substances found to have a common mechanism on 

EPA’s website at http://www.epa.gov/pesticides/cumulative/.
Page 10 of 21

DATA REQUIREMENTS

Toxicity Studies

 Repeat dose (28-day) inhalation study in the rat (870.3465)

Chemistry Studies

 None

Exposure Studies 

 None

REFRENCES

MCPP-p (acid), MCPP-p DMAS, & MCPP-p potassium salt: Revised HED Human Health

Risk Assessment, PC Code: 129046 (MCPP-p (acid)), 031520 (MCPP-p DMAS), 119046 

(MCPP-p potassium salt) (D341965; 07/26/2007)

Mecoprop-p (MCPP-p): Summary of Hazard and Science Policy Council

(HASPOC): Recommendations on the Requirement of an Immunotoxicity and Subchronic 

Inhalation Toxicity Study for mecoprop-p (MCPP-p) TXR #0056865 (1/7/2014). 

FQPA Drinking Water Assessment for Mecoprop-p (MCPP-p). Memorandum from J. Hetrick to 

M. Goodis. June 26, 2006 (DP Barcode 322772)
Page 11 of 21

Appendix A: Toxicology Profile 

Attachment 1

Table A1.1. Acute Toxicity Profile – MCPP-p (acid).

Guideline No. Study Type MRID Results Toxicity Category

870.1100 Acute oral [rat] 42947801 LD50 = 775 mg/kg III

870.1200 Acute dermal [rat] 42947802 LD50 > 2000 mg/kg III

870.1300 Acute inhalation [rat] 42947803 The study is 

unacceptable. 

UnclassifiedA

870.2400 Acute eye irritation [rabbit] 42947804 Opacity, redness, 

discharge for 72 hr

I

870.2500 Acute dermal irritation [rabbit] 42947805 Redness and 

sloughing at 10 days

III

870.2600 Skin sensitization 43749601 Non-sensitizer N/A

ANew acute inhalation studies have been submitted since the 2007 assessment

Table A1.2 Acute Toxicity Profile – MCPP-p DMAS.

Guideline No. Study Type MRID Results Toxicity Category

870.1100 Acute oral [rat] 42614701 LD50 = 763 mg/kg III

870.1200 Acute dermal [rabbit] 42614703 LD50 > 2000 mg/kg III

Table A1.3. Subchronic and Chronic Toxicity Profile – MCPP-p

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

870.3100

90-Day oral toxicity (Mouse)

MCPP-p

43059201 (1993)

Acceptable/guideline

0, 100, 1000, 2500 ppm

Male:0, 20, 220, 740 mg/kg/day

Female: 0, 30, 330, 930 

mg/kg/day

NOAEL = 20/30 mg/kg/day

LOAEL = 220/330 mg/kg/day, based on decreased body 

weight (9%). 

At HDT, increased liver enzymes, increased liver and 

kidney weights, slight increase in urea

Non-guideline 

7-Week feeding (Rat)

MCPP-p

41013910 (1986)

Acceptable/non-guideline

0, 50, 400 ppm

0, 4.8, 36 mg/kg/day

NOAEL = 36 mg/kg/day

LOAEL = not identified 

870.3200

21-Day dermal toxicity 

(Rabbit)

MCPP-p

42916401 (1993)

Acceptable/guideline

0, 10, 100, or 1000 mg/kg/day

NOAEL = 1000 mg/kg/day (HDT)

LOAEL = not identified

870.3465. Datagap

(can be satisfied with a 28-day 

HASPOC memo (TXR No. 0056865, dated 1/7/14)
Page 12 of 21

Table A1.3. Subchronic and Chronic Toxicity Profile – MCPP-p

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

Inhalation toxicity (Rat)

MCPP-p

repeat exposure study)

870.3700a

Prenatal Developmental (Rat)

MCPP-p

42815302 (1993)

Acceptable/guideline

0, 20, 50, 100 mg/kg/day

Maternal NOAEL = 50 mg/kg/day

Maternal LOAEL = 100 mg/kg/day, based on decreased 

body weight and food consumption

Developmental NOAEL = 50 mg/kg/day

Developmental LOAEL = 100 mg/kg/day, based on 

increased incidence of rudimentary cervical ribs

870.3700b

Prenatal Developmental 

(Rabbit)

MCPP-p

42815301 (1993)

Acceptable/guideline

0, 5, 20, 50 mg/kg/day

Maternal NOAEL = 50 mg/kg/day, highest dose tested

Maternal LOAEL = not identified

Developmental NOAEL = 50 mg/kg/day

Developmental LOAEL = not identified

870.3800. Reproduction

(Rat)

MCPP-p

46591804 (2003)

Acceptable/non-guideline

0, 500, 800, 1200 ppm (pre-mate)

Male: 0, 35, 54, or 83 mg/kg/day

Female: 0, 40, 63, or 94 

mg/kg/day

0, 300, 530, or 790 ppm 

(lactation)

Female: 0, 48, 86, 130 mg/kg/day

Parental NOAEL = 54/63 mg/kg/day

Parental LOAEL = 83/94 mg/kg/day, based on decreased 

body weight (8%)

Reproduction NOAEL = 83/94 mg/kg/day

Reproduction LOAEL = not identified

Offspring NOAEL = 63 mg/kg/day

Offspring LOAEL = 94 mg/kg/day, based on decreased 

mean # implants resulting in decreased # of pups born, 

decreased male pup body weight at week 4 (↓9%)

870.4100 Chronic toxicity

(Dog)

MCPP-p

44642401 (1997)

Acceptable/guideline

0, 60, 180, or 600 ppm

Male: 0, 2, 5, or 18 mg/kg/day

Female: 0, 2, 6, or 19 mg/kg/day

NOAEL 18/19 mg/kg/day (HDT)

LOAEL = not identified

870.4200 Carcinogenicity

(Mouse)

MCPP-p

44953601 (1996)

44895501 (1999)

Acceptable/guideline

0, 25, 250, 700/800, or 2500 ppm

Male: 0, 4, 40, 112, or 592 

mg/kg/day 

Female: 0, 4, 46, 188, or 732 

mg/kg/day

NOAEL = 4 mg/kg/day

LOAEL = 46 mg/kg/day, based on increased 

absolute/relative kidney weight and chronic nephropathy in 

females.

At 112/188 mg/kg/day, decreased body weight (females), 

increased absolute/relative kidney weight (females), 

increased liver weight (both sexes), and an increase in

chronic nephropathy (both sexes).

At 592/732 mg/kg/day, excess mortality

870.5100

Gene Mutation: Ames assay

MCPP-p

41013909 (1984)

Acceptable/guideline

Tested in strains TA1535, 

TA1537, TA1538, TA100, TA98 

± S9 at concentrations up to 5000 

ug/plate. 

Negative.

870.5100

Gene Mutation: Ames assay

MCPP-p

42980101 (1990)

Acceptable/guideline

Tested in strains TA1535, 

TA1537, 1538, TA100, TA98 ± 

S9 at concentrations up to 1000 

ug/plate. 

Negative

870.5100 42860803 (1993) Negative
Page 13 of 21

Table A1.3. Subchronic and Chronic Toxicity Profile – MCPP-p

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

Gene Mutation: Ames assay

MCPP-p

Acceptable/guideline

Tested in strains TA1535, 

AT1537, TA98, and TA100 at 

concentrations up to 5000 ug/plate 

±S9. 

870.5300

Gene Mutation: HGPRT

MCCP-p

42947807 (1990)

Acceptable/guideline

Tested in Chinese Hamster lung 

fibroblast V79 cells at 

concentrations up to 4000 ug/mL 

-S9 and up to 4500 ug/mL +S9. 

The 2 higher concentrations were 

cytotoxic. 

Negative for mutagenicity

870.5300

Gene Mutation: HGPRT

MCPP-p

43113401 (1993)

Acceptable/guideline

Tested in CHO cells up to 

cytotoxic concentrations (800 

ug/mL +/-S9). 

Negative for mutagenicity. 

870.5300

Gene Mutation: HGPRT

MCPP-p

42936802 (1993)

Tested in CHO cells at 

concentrations up to 3000 ug/mL 

-S9 and up to 2500 ug/mL +S9. 

The highest concentration was 

cytotoxic. 

Negative for mutagenicity

870.5375 In Vitro

Cytogenetics: Chromosomal 

Aberrations (human 

lymphocytes)

Mecoprop-p

42947806 (1990)

Acceptable/guideline

Tested in human lymphocytes at 

concentrations up to 400 ug/mL, -

S9, and up to 1600 ug/mL +S9. 

Aberrations increased at 1600 ug/mL +S9, but 76% 

decrease in mitotic index (MI) and value (4%) was within 

historical control range (0-5%). 

870.5375 In Vitro

Cytogenetics: Chromosomal 

Aberrations (human 

lymphocytes)

Mecoprop-p

43189501 (1994)

Acceptable/guideline

Tested in human lymphocytes at 

concentrations up to 600 ug/mL, -

S9, and up to 2000 ug/mL +S9. 

Dose-related trend for clastogenic activity -S9 only. 

Reduction (>50%) in MI at 600 ug/mL (20 hrs and 44 hrs) 

and at 300 ug/mL (44 hrs), but at 300 ug/mL (20 hrs) 

increase in chromosomal aberrations (chromatid and 

chromosome breaks).

870.5385 Chromosomal 

Aberration in Bone Marrow 

Chinese hamsters

mecoprop-p

41013908 (1985)

Acceptable/guideline

Dosed up to 2600 mg/kg

Negative for clastogenicity; clinical signs at all dose levels; 

2 deaths at HDT

870.5395 Micronucleus assay

Mecoprop-p

42947808 (1991)

Acceptable/guideline

Dose up to 500 mg/kg

Negative. Clinical signs at 500 mg/kg.

870.xxxx In Vivo UDS

Wistar rats

MCPP-p

Tested up to toxic dose (500 

mg/kg)

No evidence of unscheduled DNA synthesis. Clinical signs 

at HDT.

870.6200a Acute 

Neurotoxicity Study (Rat)

MCPP-p

43770801 (1995)

Acceptable/guideline

0, 175, 350, or 700 mg/kg

NOAEL = 175 mg/kg

LOAEL = 350 mg/kg, based on FOB changes (closed 

eyelids, prone body position, hypoactivity, ataxia, decreased 

number of rearings in females, increased landing foot splay 

in males, and decreased motor activity). Similar effects at 
Page 14 of 21

Table A1.3. Subchronic and Chronic Toxicity Profile – MCPP-p

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

HDT

870.6200b 

Subchronic 

Neurotoxicity/subchronic 

feeding (Rat)

MCPP-p

43908201 (1995)

Acceptable/guideline

0, 75, 500, 2500 (♂)/3000 (♀) 

ppm

Male: 0, 5, 35, 189 mg/kg/day

Female: 0, 6, 41, 240 mg/kg/day

NOAEL = 35/41 mg/kg/day

LOAEL = 189/240 mg/kg/day, based on decreased body 

weight, increased water consumption, decreased 

hematological parameters, decreased adrenal weight and 

lipid storage in adrenals, increased liver enzymes (females), 

increased liver weight, and microscopic changes, kidney 

cells in urine (males).

870.7485

Metabolism (rat)

MCPP-p

44362701 (1997)

Acceptable/guideline

5 mg/kg/day and 100 mg/kg/day

Absorption was rapid and peak plasma concentration was 

attained at 1.8 & 4.2 hours for low- and high-dose groups, 

respectively. Elimination was fast and complete regardless 

of dose levels; >90% of the administered dose was 

eliminated by 24 hrs and approximately 100% by 168 hrs. 

Major route of elimination was via urine (61-76%). A major 

metabolite was MCPP-OH

HDT: highest dose tested; BW: body weight; FOB: functional observation battery

Table A1.4. Subchronic and Chronic Toxicity Profile – MCPP 

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

870.3100

90-Day oral toxicity (Rat)

MCPP

00158359 (1985)

Acceptable/guideline

0, 50, 150, 450 ppm

male: 0, 4, 12, 37 mg/kg/day

female: 0, 5, 14, 41 mg/kg/day

NOAEL = 12 mg/kg/day

LOAEL = 37 mg/kg/day, based on increased absolute and 

relative kidney weight

Non-guideline 

7-Week feeding (Rat)

MCPP

41013910 (1986)

Acceptable/non-guideline

0, 50, 400 ppm

0, 4.8, 36 mg/kg/day

NOAEL = 36 mg/kg/day

LOAEL = not identified 

870.3700a

Prenatal Developmental (Rat)

MCPP

00164569 (1980)

Acceptable/guideline

0, 20, 50, 125 mg/kg/day

Maternal NOAEL = 125 mg/kg/day

Maternal LOAEL = not identified

Developmental NOAEL = 50 mg/kg/day

Developmental LOAEL = 125 mg/kg/day, based on 

increased intrauterine death, decreased crown-rump length,

and incomplete/absent sternebrae ossification

870.3700b

Prenatal Developmental 

(Rabbit)

MCPP

00144282 (1980)

Acceptable/guideline

0, 12, 30, 75 mg/kg/day

Maternal NOAEL = 30 mg/kg/day

Maternal LOAEL = 75 mg/kg/day based on decreased body 

weight gain

Developmental NOAEL = 75 mg/kg/day

Developmental LOAEL = not identified

870.4100 Chronic toxicity

(Rat)

MCPP

40937501 (1986)

Acceptable/guideline

0, 20, 100, or 450 ppm

Male: 0, 1.1, 5.5, 22.2 mg/kg/day

Female: 0, 1.4, 6.9, or 27.9 

mg/kg/day

NOAEL = 6 mg/kg/day

LOAEL = 22 mg/kg/day, based on increased 

absolute/relative kidney weight in males; no changes in 

body weight, hematology, clinical chemistry, or urinalysis

870.5100 00158361 (1981) Negative. 
Page 15 of 21

Table A1.4. Subchronic and Chronic Toxicity Profile – MCPP 

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

Gene Mutation: Ames assay

MCPP

Acceptable/guideline

strains TA1535, TA1537, 

TA1538, TA100, TA98 ± S9 at 

concentrations up 5000 ug/plate. 

870.5375 In Vitro Mammalian 

Cytogenetics: Chromosomal 

Aberrations (human 

lymphocytes)

MCPP

42936803 (1993)

Acceptable/guideline

Tested at concentrations up to 

1000 ug/mL (-S9) and up to 5000 

ug/mL (+S9). 

Clastogenic with activation, but only at a cytotoxic 

concentration (2500 ug/mL) Negative with -S9. Only 

chromatid and chromosome breaks were seen. Evidence of 

chromosomal aberrations at cytotoxic concentration with 

S9.

870.5385 Chromosomal 

Aberration in Bone Marrow 

Chinese hamsters

Mecoprop

00158362 (1985)

Classified inconclusive due to 

deficiencies.

dosed up to 3800 mg/kg

MCPP was weakly positive for clastogenic activity in HDT 

animals sacrificed at 6 hours and accompanied by a 56% 

decrease in mitotic index (MI). Considered equivocal 

because the types of induced aberrations (chromatid and 

chromosome breaks) would likely induce cell killing and 

would be lost from the daughter cells. At 24 hours, 

aberrations were increased in HDT animals, but not with 

statistical significance. One death and clinical signs at HDT. 

Table A1.5. Subchronic and Chronic Toxicity Profile – MCPP-p-DMA

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

870.3200

21-Day dermal toxicity (Rat)

MCPP-p DMAS

43638102 (1995)

Acceptable/guideline

9, 12, 120, 1000 mg/kg/day

NOAEL = 1000 mg/kg/day (HDT)

LOAEL = not identified

870.5100

Gene Mutation: Ames assay

MCPP-p-DMA

42860801 (1993)

Acceptable/guideline

strains TA1535, AT1537, TA98, 

and TA100 at concentrations up 

to 5000 ug/plate ±S9. 

Negative

870.5395 Micronucleus assay 

(mouse)

Mecoprop-p-DMA

42860804 (1993)

Acceptable/guideline

Doses up to 576 mg/kg

Negative assay. Clinical signs seen at MDT and HDT 48 

hours after treatment. 

870.5375 In Vitro Mammalian 

Cytogenetics: Chromosomal 

Aberrations in human 

lymphocytes

Mecoprop-p-DMA

42936803 (1993)

Acceptable/guideline

Tested in human lymphocytes at 

concentrations up to 1000 ug/mL

(-S9) and up to 5000 ug/mL 

(+S9). 

Clastogenic with activation, but only at a cytotoxic 

concentration (2500 ug/mL) Negative with -S9. Only 

chromatid and chromosome breaks were seen. Evidence of 

chromosomal aberrations at cytotoxic concentration with 

S9.

870.7485

Metabolism (rat)

MCPP-p DMAS

44362702 (1997)

Acceptable/guideline

5 mg/kg (single dose)

MCPP-p DMAS was rapidly absorbed. Maximum plasma 

concentrations were attained at 2 hours. Within 24 hours, 

83% of the dose was eliminated, & elimination half-time 

was 6.6 hours. Urine was the primary route of elimination, 

accounting for 86% of the administered dose over a 168-

hour time period. Most of the eliminated radioactivity was 

associated with parent compound. A hydroxylated 
Page 16 of 21

Table A1.5. Subchronic and Chronic Toxicity Profile – MCPP-p-DMA

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

metabolite, MCPP-OH, accounted for 22% of the 

administered dose detected in the urine.

870.7485

Metabolism (rat)

MCPP-p DMAS

43717201 (1995)

Acceptable/non-guideline

(

14C)-MCPP-p DMAS was incubated in vitro with rat 

plasma, stomach content, gastro-intestinal tract (GIT) or 

post-mitochondrial liver fraction (S9) for 30 minutes. All 

incubated extracts were subjected to HPLC analysis. 

Results indicated that all of the administered (14C)-

MCPP-p DMAS in plasma, stomach contents, gastrointestinal tract and liver (S9) was present as the ionized 

form of (14C)-MCPP-p.
Page 17 of 21

Table A1.6. Subchronic and Chronic Toxicity Profile – MCPP-p-EHE

Guideline No.

Study Type/Chemical

MRID (year)

Classification/ Doses

Results

870.3200

21-Day dermal toxicity (Rat)

MCPP-p EHE

43638101 (1995)

Acceptable/guideline

0, 15, 150, 1000 mg/kg/day

NOAEL = 1000 mg/kg/day (HDT)

LOAEL = not identified

870.5100

Gene Mutation: Ames assay

MCPP-p-2-EHE

42860802 (1993)

Acceptable/guideline

Tested in strains TA1535, 

AT1537, TA98, and TA100 at 

concentrations up to 5000 ug/plate 

±S9. 

Negative

870.5300

Gene Mutation: HGPRT

Mecoprop-p-2-EHE

42936804 (1993)

Acceptable/guideline

Tested in CHO cells at 

concentrations up to 250 ug/mL -

S9 and up to 500 ug/mL +S9. 

Negative up to cytotoxic and/or solubility limits. 

870.5395 Micronucleus assay 

(mouse)

Mecoprop-p-2-EHE

42860805 (1993)

Acceptable/guideline

Dosed up to 3128 mg/kg

Negative asses. Clinical signs and mortality at HDT.

870.5375 In Vitro Mammalian 

Cytogenetics: Chromosomal 

Aberrations in human 

lymphocytes

Mecoprop-p-2-EHE

42936805 (1993)

Acceptable/guideline

Tested in human lymphocytes at 

concentrations up to 80 ug/mL (-

S9) and up to 320 ug/mL (+S9). 

MCPP-p-EHE induced structural aberrations (chromatid and 

chromosome breaks) at the highest +S9 concentration, 

which was insoluble but non-cytotoxic. 

870.7485

Metabolism (rat)

MCPP-p EHE

44362702 (1997)

Acceptable/guideline

5 mg/kg (single dose)

MCPP-p EHEs was rapidly absorbed; maximum plasma 

concentrations were attained at 3.6 hours. Within 24 hours, 

68% of the dose was eliminated, & elimination half-time 

was 8.4 hours. Urine was the primary route of elimination, 

accounting for 71% of the administered dose over a 168-

hour time period. Most of the eliminated radioactivity was 

associated with parent compound. A hydroxylated 

metabolite, MCPP-OH, accounted for 16% of the 

administered dose detected in the urine.

Toxicology Data Requirements

The toxicology data requirements (40 CFR 158.340) for the non-food uses of MCPP-p are presented below. Use of 

the new guideline numbers does not imply that the new (1998) guideline protocols were used.

Study

Technical

Required Satisfied

870.1100 Acute Oral Toxicity ......................................................

870.1200 Acute Dermal Toxicity .................................................

870.1300 Acute Inhalation Toxicity .............................................

870.2400 Primary Eye Irritation ...................................................

870.2500 Primary Dermal Irritation .............................................

870.2600 Dermal Sensitization.....................................................

yes

yes

yes

yes

yes

yes

yes

yes

yes2

yes

yes

yes
Page 18 of 21

Study

Technical

Required Satisfied

870.3100 Oral Subchronic (rodent) ..............................................

870.3150 Oral Subchronic (nonrodent) ........................................

870.3200 21-Day Dermal .............................................................

870.3250 90-Day Dermal .............................................................

870.3465 90-Day Inhalation .........................................................

CR

CR

no

yes

yes

yes

yes

yes

yes3

no4

870.3700a Developmental Toxicity (rodent)..................................

870.3700b Developmental Toxicity (nonrodent)............................

870.3800 Reproduction.................................................................

yes

yes

yes

yes

yes

yes

870.4100a Chronic Toxicity (rodent) .............................................

870.4100b Chronic Toxicity (nonrodent) .......................................

870.4200a Oncogenicity (rat) .........................................................

870.4200b Oncogenicity (mouse)...................................................

870.4300 Chronic/Oncogenicity...................................................

CR1

CR1

CR1

CR1

CR1

yes

yes

-

yes

-

870.5100 Mutagenicity—Gene Mutation – bacterial....................

870.5375 Mutagenicity—Structural Chromosomal Aberrations..

870.5550 Mutagenicity—Other Genotoxic Effects ......................

yes

yes

yes

yes

yes

yes

870.6100a Acute Delayed Neurotoxicity (hen) ..............................

870.6100b 90-Day Neurotoxicity (hen)..........................................

870.6200a Acute Neurotoxicity Screening Battery (rat).................

870.6200b 90-Day Neurotoxicity Screening Battery (rat)..............

870.6300 Developmental Neurotoxicity .......................................

CR

CR

yes

yes

CR

-

-

yes

yes

-

870.7485 General Metabolism......................................................

870.7600 Dermal Penetration .......................................................

870.7800 Immunotoxicity.............................................................

CR

CR

Yes

yes

yes

-

5

1 Not required under the registered use patterns;2

submitted since last risk assessment; 3satisfied by 28-day dermal study; 

4HASPOC determined study is required (TXR No. 0056865, dated 1/7/14); 5HASPOC waived this requirement (TXR No. 

0056865, dated 1/7/14).
Page 19 of 21

Attachment 2. MCPP-p Endpoints and Doses for Risk Assessment

Table A.2.1 Toxicological Doses and Endpoints for MCPP-p for Exposure Assessment

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

RfD

Level of 

Concern

Study and Toxicological Effects

Acute Dietary

(Females 13-49 

years of age)

NOAEL = 

50 mg/kg/day

UFA = 10x

UFH = 10x

aRfD = 0.5 

mg/kg/day

Developmental toxicity in rats with 

MCPP-p. LOAEL = 100 mg/kg/day 

based on an increased incidence of

rudimentary cervical ribs. 

Acute Dietary 

(General 

Population, 

including infants 

and children)

NOAEL = 

175 

mg/kg/day

UFA = 10x

UFH = 10x

aRfD = 1.75 

mg/kg/day 

Acute neurotoxicity in rats with MCPPp. LOAEL = 350 mg/kg/day based on 

FOB changes (closed eyelids, prone 

body position, hypoactivity, ataxia); 

decreased rearings in females; increased

landing foot splay in males and decr 

motor activity. 

Chronic Dietary 

(All Populations)

NOAEL = 

4 mg/kg/day

UFA = 10x

UFH = 10x

cRfD = 0.04 

mg/kg/day 

Mouse carcinogenicity study with 

MCPP-p. LOAEL = 46 mg/kg/day 

based on increased kidney wt and 

chronic nephropathy in females. 

Incidental Oral 

Short-Term 

(1-30 days) and 

IntermediateTerm 

(1-6 months)

NOAEL = 

35 mg/kg/day

UFA = 10x

UFH = 10x

LOC = 100 Subchronic feeding/Subchronic 

neurotoxicity study in rats with MCPPp. LOAEL = 189 mg/kg/day based on 

decreased body weight, increased water 

consumption; decreased hematological 

parameters, decreased absolute adrenal 

weight and lipid storage in adrenals, 

increased liver enzymes (females), 

increased absolute/relative liver weight 

and microscopic changes; kidney cells 

in urine of high-dose males. 

Dermal 

(all durations)

N/A N/A N/A No toxicity at 1000 mg/kg/day and no 

developmental toxicity concerns by 

dermal route. 

Inhalation

(short-term, 

intermediateterm)

NOAEL = 

35 mg/kg/day

UFA = 10x

UFH = 10x

UFDB = 10X

Inhalation 

absorption rate 

= 100%

LOC = 100 Subchronic feeding/Subchronic 

neurotoxicity study in rats – see above.

Cancer Classification: "Suggestive Evidence of Carcinogenicity, but Not Sufficient to Assess 

Human Carcinogenic Potential"

Point of Departure (POD) = A data point or an estimated point derived from dose-response data which is used to 

mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human 

exposures.
Page 20 of 21

NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level.

UF= uncertainty factor; UFA = extrapolation from animal to human (interspecies). UFH = potential variation in 

sensitivity among members of the human population (intraspecies). UFDB = database uncertainty factor for lack of 

the subchronic inhalation toxicity study. aRfD = acute reference dose. cRfD=chronic reference dose; LOC = level 

of concern. N/A = not applicable. 

Table A.2.2 Toxicological Doses and Endpoints for MCPP-p for Occupational Exposure Assessment

Exposure/

Scenario

Point of 

Departure

Uncertainty 

Factors

Level of 

Concern

Study and Toxicological Effects

Dermal 

(all durations)

N/A N/A N/A No toxicity at 1000 mg/kg/day and 

there are no developmental concerns for 

this route of exposure. 

Inhalation

(all durations)

NOAEL = 

35 mg/kg/day

UFA = 10x

UFH = 10x

LOC = 100 Subchronic feeding/Subchronic 

neurotoxicity in rats with MCPP-p. 

LOAEL = 189 mg/kg/day based on 

decreased body weight, increased water 

consumption; decreased hematological 

parameters, decreased absolute adrenal 

weight and lipid storage in adrenals, 

increased liver enzymes (females), 

increased absolute/relative liver weight

and microscopic changes; kidney cells 

in urine of high-dose males. 

Cancer Classification: "Suggestive Evidence of Carcinogenicity, but Not Sufficient to Assess 

Human Carcinogenic Potential"

Point of Departure (POD) = A data point or an estimated point derived from dose-response data which is used to mark the beginning of 

extrapolation to determine risk associated with lower environmentally relevant human exposures.

NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UFA = extrapolation from 

animal to human (interspecies). UFH = potential variation in sensitivity among members of the human population (intraspecies). MOE = margin 

of exposure. LOC = level of concern. N/A = not applicable.
Page 21 of 21

Appendix B: Chemistry

1.0 Identification of Active Ingredient

Table B.1.1Test Compound Nomenclature

Chemical Structure

Empirical Formula C10H11ClO3

Common name Mecoprop-p, MCPP-p

Company experimental name (R)-(+)-2-(4-chloro-2-methylphenoxy)propanoic acid

IUPAC name (R)-2-(2-methyl-4 chlorophenoxy)propionate

CAS Registry Number 16484-77-8, 66423-09-4, 66423-05-0

Chemical Class Chlorophenoxy 

2.0 Physical and Chemical Properties

Table B.1.2 Physicochemical Properties of MCPP-p

Parameter Value Reference

Molecular Weight 214.6g/mole D263488

Melting point/range 93.5-97.5oC D263488

pH 2.9 (1% w/v suspension) D263488

Density 500-700 g/L EFED Risk Assessment

Water solubility (20°C) 620 mg/L @ 20oC EFED Risk Assessment

Solvent solubility (20°C) >100 g/100g in acetone, 

ethanol 

Farm Chemical Handbook 

2002

Vapor pressure (25°C) 5.1x 10-5torr EFED Risk Assessment

Dissociation constant, pKa 2.0x10-4(pKa =3.7) D263488

Octanol/water partition coefficient, 

logPOW

-0.19 @ pH 7 MCPP-p Task Force