UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY AND 

POLLUTION PREVENTION 

MEMORANDUM 

Date: February 5, 20 15 

SUBJECT: Thidiazuron: Tier I Review of Human Incidents 

PC Code: 120301 

Decision No.: 498947 

Petition No.: NA 

Risk Assessment Type: NA 

TXR No.: NA 

MRID No.: NA 

DP Barcode: 0425469 

Registration No.: NA 

Regulatory Action: NA 

Case No.: NA 

CAS No.: 51707-55-2 

40 CFR: NA 

FROM: Shanna Recore, Industrial Hygienist 

Toxicology and Epidemiology Branch 

Health Effect Division (7509P) 

J/1 Elizabe~~~vans, Environmental Protection Specialist Utt 

/" Toxicology and Epidemiology Branch 

Ver.Apr.08 

Health Effects Division (7509P) 1). J /if/!<. ot/. -U 5 THROUGH: David Miller, Acting Branch Chie 1 '/jf/ 

Toxicology and Epidemiology Branch 

Health Effects Division (7509P) 

TO: Ronnie Bever, Risk Assessor 

Risk Assessment Branch VII 

Health Effects Division (7509P) 

and 

Khue Nguyen, Chemical Review Manager 

Risk Management & Implementation Branch I 

Pesticide Re-evaluation Division (7508P) 

Summary and Conclusions 

Based on the low frequency and low severity of incident cases reported for thidiazuron in both 

IDS and SENSOR-Pesticides, there does not appear to be a concern at this time that would 

warrant further investigation. The Agency will continue to monitor the incident information and 

if a concern is triggered, additional analysis will be included in the risk assessment. 

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Detailed Review 

I. ACTION REQUESTED 

This review is intended to fulfill our requirement to docket summaries of incident data that were 

reported to the Agency, as well as to ensure human incident data and the Agricultural Health 

Study (AHS) are part of the problem formulation phase of registration review. 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. However, incident 

information can be an important source of feedback to the Agency: incidents of severe outcome, 

or a suggested pattern or trend among less severe incidents, can signal the Agency to further 

investigate a particular chemical or product. Observational epidemiology studies relate the risk 

of disease, e.g., cancer, and exposure to an agent such as a pesticide product in the general 

population or specific sub-groups like pesticide applicators. 

II. BACKGROUND 

Thidiazuron is used as a pre-harvest cotton defoliant or growth regulator. It removes green leaves 

and immature fruiting structures, which contribute to cotton staining. There are no registered 

residential uses. 

For this evaluation, both the OPP Incident Data System (IDS) and the Centers for Disease 

Control and Prevention/National Institute for Occupational Safety and Health (CDC/NIOSH) 

Sentinel Event Notification System for Occupational Risk-Pesticides (SENSOR) databases were 

consulted for pesticide incident data on the active ingredient thidiazuron (pc code: 120301). The 

purpose of the database search is to identify potential patterns in the frequency and severity of 

the health effects attributed to thidiazuron exposure. Thidiazuron is not included in the AHS, 

and therefore this study does not provide information for this report. 

III. RESULTS/DISCUSSION 

a. IDS (Incident Data System) 

OPP's IDS includes reports of alleged human health incidents from various sources, including 

mandatory Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) Section 6(a)(2) reports 

from registrants, other federal and state health and environmental agencies, and individual 

consumers. Since 1992, OPP has compiled these reports in IDS. IDS contains reports from 

across the U.S. and most incidents have all relevant product information recorded. Reports 

submitted to the IDS represent anecdotal reports or allegations only, unless otherwise stated in 

the report. 

IDS records incidents in one of two modules: Main IDS and Aggregate IDS: 

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o Main IDS contains incidents resulting in higher severity outcomes and provides 

more detail with regard to case specifics. This system stores incident data for 

death, major and moderate incidents, and it includes information about the 

location, date and nature of the incident. Main IDS incidents involving only one 

active ingredient (as opposed to pesticide products with multiple active 

ingredients) are considered to provide more certain information about the 

potential effects of exposure from the pesticide. 

o Aggregate IDS contains incidents resulting in less severe human incidents (minor, 

unknown, or no effects outcomes). These are reported by registrants only as 

counts in what are aggregate summaries. 

For the Main IDS, from January 1, 2010 to December 30,2014, there were 0 incidents reported 

involving thidiazuron. 

In Aggregate IDS, from January 1, 2010 to December 30, 2014, there was 1 incident reported 

involving thidiazuron. This incident was classified as minor severity. Overall, there are few 

incidents involving thidiazuron reported to IDS. · 

b. SENSOR-Pesticides 

The SENSOR-Pesticides database covers 12 states from 1998-2011, although reporting varies 

from state to state. Cases of pesticide-related illnesses are ascertained from a variety of sources, 

including: reports from local Poison Control Centers, state Department of Labor workers' 

compensation claims when reported by physicians, reports from State Departments of 

Agriculture, and physician reports to state Departments of Health. Although both occupational 

and non-occupational incidents are included in the database, SENSOR-Pesticides focuses on 

occupational pesticide incidents, and is of particular value in providing that information. The 

state coordinator at each of the 12 respective state Departments of Health conducts case followup activities such as obtaining medical records to verify symptoms and severity. Using 

standardized protocol and case definitions derived from poison center reporting, the state 

SENSOR-Pesticide coordinator enters the incident information into the state-based system which 

is sent to NIOSH annually to be aggregated. 

A review of SENSOR-Pesticides 1998-2011 identifies 16 cases involving thidiazuron (pc code 

120301), one case involved a single ai. This case occurred in Texas in 1998 and was low in 

severity. The case is described in SENSOR as follows, "Complainant heard an aerial application 

occurring nearby. She went outside and saw an aerial applicator spraying a cotton field. " 

c. Agricultural Health Study (AHS) 

The AHS is a high quality, prospective epidemiology study evaluating the link between pesticide 

use and various health outcomes including cancer. The AHS includes private and commercial 

pesticide applicators and their spouses. If there are AHS findings relevant to a particular 

pesticide going through registration review, the Agency will ensure they are considered in the 

problem formulation/scoping phase of the process and, if appropriate, fully reviewed in the risk 

assessment phase of the process. The AHS includes information on use of 80 different pesticide 

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active ingredients commonly used in agriculture. Thidiazuron is not included in the AHS, and 

therefore this study does not provide information for this report. 

IV. CONCLUSION 

Based on the low frequency and low severity of incident cases reported for thidiazuron in both 

IDS and SENSOR-Pesticides, there does not appear to be a concern at this time that would 

warrant further investigation. The Agency will continue to monitor the incident information and 

if a concern is triggered, additional analysis will be included in the risk assessment. 

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