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Attachment C

Draft Case Study

Integrating Human Incident Data into 

Regulatory Risk Assessment

Diazinon Human Incident Data

Office of Pesticide Programs

Office of Pollution Prevention and Toxic Substances

U.S. Environmental Protection Agency

FIFRA Scientific Advisory Panel

February 2-5, 2010
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C.I. INTRODUCTION

This document focuses primarily on human incident data – and describes the ways 

in which this type of data can be appropriately used to inform the risk assessment of 

pesticides. Incident data typically contain information on potential acute human 

exposures and the resulting health outcomes that might be associated with them; 

Reports vary in quality and level of detailed narratives describing the exposure scenario; 

they are self reported cases of exposure and resulting outcomes collected in a 

systematic way. Despite these limitations, Incident datasets are an important resource 

of health surveillance information on registered pesticides.

Although OPP could have chosen many other pesticides for which incident data 

have impacted our regulatory decision making, OPP selected diazinon for this case 

study because it has a robust animal toxicology data base, a regulatory history that 

includes recent, significant changes in allowable exposures, and a high frequency of 

reported incidents. Additionally, diazinon is a chemical currently being re-evaluated 

under OPP‟s registration review program, and thus its effects and exposure assessment 

is being updated. The main intent of this case study is to illustrate how human incident 

data can be integrated with current hazard and exposure information, and be 

considered in light of previous risk mitigation activities. As described below, diazinon 

human incident data mainly demonstrate the impact of previous regulatory risk 

mitigation decisions, without meriting a recommendation to reconsider the most recent 

hazard and/or exposure assessment.

Please note that this case study has been prepared as an illustrative case study

focused on reviewing incident data and acute effects. It does not represent a full 

analysis of all available information concerning incident data, epidemiology and 

toxicology.

The case study is organized into four sections:

I. Introduction: OPP‟s use of human incident data

II. Regulatory background:Diazinon

III. Review of human incident data: Diazinon

IV. Overall Conclusion/Summary: overall consideration of human incident data 

I. OVERVIEW OF INCIDENT DATABASES

EPA relies primarily on incident data collected under the Federal Insecticide, 

Fungicide and Rodenticide Act (FIFRA) and implementing regulations, which require

pesticide registrants to notify EPA if and when they become aware of “[i]nformation 

about incidents affecting humans or other non-target organisms ... [where] a person or 

non-target organism may have been exposed to a pesticide ... [and] that the person or 
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non-target organism suffered a toxic or adverse effect, or may suffer a delayed or 

chronic adverse effect in the future ... [and] [t]he registrant has or could obtain 

information concerning where the incident occurred, the pesticide or product involved, 

and the name of a person to contact regarding the incident” (CFR §159.184).

EPA stores information reported under this provision in the Incident Data System 

(IDS). IDS is maintained by OPP and incorporates data submitted by registrants, as 

well as other incidents reported directly to EPA. In addition to the IDS, the Agency 

draws upon additional human incident data collected by other entities: the American 

Association of Poison Control Centers (PCC), the National Pesticide Information Center 

(NPIC), the Centers for Disease Control and Prevention/National Institute for 

Occupational Safety and Health Sentinel Event Notification System for Occupational 

Risk (NIOSH SENSOR) and the California Pesticide Illness Surveillance Program 

(PISP). These additional incident data sources allow the Agency to determine 

reproducibility and consistency of reported symptoms among the general population 

and certain sensitive subpopulations.

A. Human Incident Databases: Strengths and Limitations

In addition to basic demographic information, incident data provide exposure and 

hazard information on registered pesticides:

Types of exposure information include:

o Occupational (agricultural or residential professional applicator) versus 

non-occupational (residential) 

o Narratives (describing how/why the exposure occurred)

o Product information

o Scope of database (national/non-national coverage)

Types of hazard information include:

o Severity rankings

o Symptoms

When evaluating human incident data, it is important to understand not only the 

strengths but also the limitations of the data. The main limitation of human incident 

information is the difficulty associated with establishing a causal determination between 

exposure and outcome. Another significant limitation is the lack of information that 

would provide better context to evaluate the significance of incident data. For example, 

without data on extent of use in the areas covered by a data source, EPA may be 

unable to determine whether a high frequency of incidents indicates that one pesticide 

poses a greater problem than other pesticides or whether the increased frequency 

reflects differences in market share of pesticides sold. 

Additionally, incidents are mainly self-reported, and typically neither exposures to a 

pesticide nor reported symptoms are easily verifiable (although as described in this 

section, some databases involve more follow-up and confirmation than others). Finally, 

because of the self-reported nature of most incidents, these databases are likely to 
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underestimate the incidence of exposures that actually do occur due to underreporting.

Some may be less inclined to report a work related adverse event if it might lead to 

unemployment. Because of these limitations, the Agency seldom relies solely on one

incident data source to make determinations about whether there is concern for the safe 

use of a registered pesticide and/or pesticide product, but draws on several sources in 

conjunction with other types of hazard information. 

The following descriptions are intended to provide more detailed information about

the strengths and weaknesses of each database. 

Incident Data System (IDS): IDS is national in scope and includes reports on 

both occupational and non-occupational incidents, but like most incident 

databases it includes more information about non-occupational incidents than 

occupational incidents. Different from other sources, IDS includes narrative

information about exposure scenarios. Agency reviewers must analyze and distill 

each narrative to determine potential associations, which is resource intensive. 

As IDS is populated mostly by registrant-submitted information, the Agency has 

relatively high confidence in the product information provided because of the 

accuracy and verification of the information. 

IDS also includes hazard information and severity of reported effects. These 

severity categories include: 

o H-A: Human fatality, 

o H-B: Human major incident, symptoms may have been life threatening, or 

resulted in adverse effects or in residual disability

o H-C Human moderate incident, symptoms were not life threatening and 

the person returned to pre-exposure state of health with no residual 

disability

o H-D Human minor incident, symptoms resolved rapidly and may involve 

skin, eye, or respiratory irritation

o H-E symptoms unknown or not specified. 

These categories are included for each incident (as specified in 40CFR 

§159.184); however, upon review of narratives, severity categories often appear 

inflated compared to other databases (and subsequently, the Agency has less 

confidence in these classifications than it does in those from other sources of 

information). 

Poison Control Center (PCC): PCC is national in scope and provides mainly

non-occupational incidents. The incident database does not include narrative 

information, which makes it difficult to assess patterns of exposure scenarios. 

The information available to PCC often does not identify the specific pesticide 

product involved, and the Agency relies on an EPA generated table that matches 

product identification numbers in the PCC to EPA product identification numbers 

(and subsequently, pesticide specific information). This effort has resulted in 
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approximately 80% of PCC incidents including specific information identifying the 

pesticide product. 

As for hazard information, PCC provides severity rankings and symptom 

information that are designated/recorded by trained health care professionals, 

and therefore the Agency has relatively high confidence in this information. PCC 

also provides some information about the likelihood of the adverse effect being a 

result of the reported exposure. Overall, PCC provides good information about 

national trends, frequency of incidents for pesticides (which is somewhat limited 

by PCC‟s product database), as well as the hazard potential for particular 

pesticides. On the other hand, exposure scenario information is difficult to 

ascertain. 

National Pesticide Information Center (NPIC): Although NPIC also collects 

pesticide incident data, it is primarily intended to provide objective data on

pesticides. Similar to IDS and PCC, the incidents reported in this database are 

mainly non-occupational. NPIC incidents include narratives and product 

information when the caller provides it. The scope is national; however, there are 

significantly fewer incidents reported to NPIC than are reported to PCC or IDS. 

Hazard information includes severity rankings as well as routes of exposure and 

symptoms, which are recorded by trained personnel. NPIC also provides 

information on how likely is the link between exposure and adverse effect (which 

they call a certainty index). Because the NPIC operation is not as extensive as 

PCC, and does not involve the same number of incidents as PCC and IDS, the 

data are less useful for detecting trends. The information, particularly in the 

incident narratives and/or in the hazard ratings, can, however, help to 

corroborate conclusions drawn from other incident data sources. NPIC also 

publishes annual reports and analyses in the open literature which are valuable 

resources to the Agency. 

National Institute of Occupational Safety and Health (NIOSH) Sentinel Event 

Notification System for Occupational Risk (SENSOR): The NIOSH SENSOR 

database is not national in scope, but includes 12 participating states. This 

system captures pesticide-related acute illness/injury occurring in these state 

populations. This database collects information on illness and injuries resulting 

from both occupational and non-occupational exposures. Unlike other incident 

databases, the majority of the incidents in NIOSH SENSOR involve occupational 

cases. These include narratives and product information based on input by 

trained professionals. 

Hazard information includes severity rankings, and narrative information can 

include information on symptoms and treatment. Overall, NIOSH SENSOR 

provides good information on both occupational and non-occupational incidents, 

and it sometimes provides valuable insights into the hazard and/or exposure 

potential of a pesticide. NIOSH SENSOR also conducts analyses of its own data 
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and publishes these in the Morbidity and Mortality Weekly, which are a valuable 

resource to the Agency.

Pesticide Illness Surveillance Program (PISP): The scope of the database is 

limited to California, but as a major agricultural state in the U.S. it contains a 

substantial body of information. PISP is also a resource both for wellcharacterized occupational incidents and for non-occupational incidents. The 

database includes narratives and product information that is entered by trained 

professionals who conduct follow-up on each reported case. Although there are 

no severity rankings, there are other fields (such as days lost from work and days 

hospitalized) which can be used as proxies for severity. Symptom and 

sometimes treatment information is available in narrative fields. PISP also 

provides information assessing the strength of the evidence of a link between 

exposure and adverse effects (in the field designated “Relationship”). Overall, 

PISP provides good information on both occupational and non-occupational 

incidents, and sometimes it provides valuable insights into the hazard and/or 

exposure potential of a pesticide. Additionally, PISP data is publicly available.

B. How does OPP Evaluate Human Incident Data?

Currently, OPP evaluates human incident data on a case-by-case, chemical-specific 

basis. Incidents from each database are analyzed for the nature and severity of the 

effects reported (e.g., deaths, gastrointestional problems, etc.), frequency of more 

severe incidents, and patterns/trends of reported symptoms, The exposure potential is 

also evaluated including the factors affecting exposure of products (e.g., the frequency 

of incidents/trends over time, patterns/trends of exposure scenarios).

Additionally, narratives of more severe incidents are often evaluated with respect to 

any temporal association that might exist between the time-of-exposure and the effects 

reported to determine whether an association between the exposure and the effect is 

supported. For example, if a severe incident occurs at the time of exposure, or if 

symptoms and health conditions occur immediately after exposure without prior medical 

history, and the symptoms progress over time or are reproduced upon re-exposure, 

then EPA would likely regard that severe incident as likely due to pesticide exposure.

When preliminary analyses of one data source indicate a possible hazard/exposure 

potential of interest, additional databases are consulted for consistency and 

reproducibility, and the overall potential for a relationship between exposure and 

adverse outcome is considered in light of all other available information (e.g., animal 

toxicity profile and mode of action, etc.) using the Bradford Hill causal criteria of

consistency, reproducibility, temporal association and biological plausibility.

C. How does OPP use Incident Data?

Human observational data in general provide real-world feedback on pesticide 

products being used by the public. In particular, OPP uses human incident information, 

on balance, for several purposes. First, the program uses incident data to inform risk 
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reduction/prevention through risk assessment/risk management activities (as illustrated 

by the diazinon case study). For example, incident information can indicate a need for 

new risk management measures, and it can help assess the success of risk mitigation 

actions after they are implemented. Secondly, as a risk communication tool, incident 

data provide insight into the potential nature, extent and severity of illnesses or injuries

resulting from exposure to pesticide products to help inform decision makers, 

stakeholders and the public in general about their safe use. Thirdly, incident information 

is an integral part of OPP‟s performance accountability system, to ensure that the risk 

management actions taken by OPP to protect human health and the environment are

effective. Lastly, incident information can be useful in targeting enforcement activities,

and it can serve as a source for information about compliance with incident reporting 

regulations. 

CASE STUDY ON THE REVIEW OF INCIDENT DATA: DIAZINON

II. REGULATORY BACKGROUND: DIAZINON

Diazinon, first marketed in 1956, is a restricted use organophosphate (OP) pesticide 

currently registered for use on a number of fruits, vegetables, nuts, and ornamentals 

grown outdoors in nurseries. It is also used in cattle ear tags. Prior to 2000, diazinon 

was one of the most widely used insecticides available on the residential market. In 

2000, based on potential risks to children identified during the reregistration process 

(the previous OPP pesticide re-evaluation program), all residential use diazinon 

products were cancelled. Sales of all indoor residential use products ended in 2002, and 

sales of all outdoor residential use products ended in 2004. Due to these risk mitigation 

efforts outdoor consumer use of diazinon and professional use of diazinon on turf and 

ornamentals decreased around 10-fold from 2000 to 2005/2006.

During the re-registration process potential risks to occupational workers were also

identified and subsequently mitigated via increased restricted entry intervals (REIs), 

prohibition of foliar application on most vegetables and elimination of aerial application 

and granular uses. Engineering controls were also required. Consequently, 

professional use of diazinon in California in agricultural and non-agricultural sectors also 

decreased during the period from 2000-2007 by over half (see Appendix A for details on 

chemical use trends).

In 2008, EPA conducted a review of diazinon incidents in IDS during the problem 

formulation phase of the next round of registration review, and found a high number of 

incidents as well as a distinct trend of incidents reported over time. Subsequently, other 

incident databases were consulted and considered in light of the most recent risk 

assessment. This case study summarizes those incident data reviews and findings.
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III. HUMAN INCIDENT DATA REVIEW: DIAZINON

A. Summary of Animal Toxicology and Mode of Action

Prior to review of human incident data, consideration of the available animal 

toxicology and mode of toxicological action is an important step towards interpretation of 

these human symptoms. Because human incident data primarily report events from 

acute exposure, the review of acute animal toxicology data is most relevant. From 

review of the animal toxicity information, diazinon has a low acute toxicity via oral, 

dermal or inhalation routes of exposure. It is minimally irritating to the eyes and is not 

considered a skin sensitizer. Diazinon induces cholinergic signs or symptoms of toxicity 

typical of an organophosphate (OP) pesticide. Like other OPs, diazinon inhibits the 

enzyme acetylcholinesterase in the central and peripheral nervous systems. This 

inhibition leads to accumulation of the acetylcholine neurotransmitter at synapses and 

ultimately to disruption of normal nerve transmission, which results in physiological and 

behavioral changes. As with the other OPs, at extremely high doses, death can occur 

from diazinon exposure.

The available animal toxicology database is robust and includes data from multiple 

species (hens, mice, rats, rabbits, and dogs). Clinical signs of toxicity observed in 

laboratory animals include: tremors, convulsions, salivation, and dyspnea (labored 

breathing). Inhibition of plasma, erythrocyte and/or brain cholinesterase activity occurs 

by all routes (oral, dermal, and inhalation) and for all durations of exposure. In animal 

studies, diazinon does not inhibit neurotoxic esterase (NTE) and it was not found to 

induce organophosphate-induced delayed neuropathy (OPIDN). Further, it has not 

been shown to cause histopathological lesions of the nervous system. 

The risk assessment conducted by OPP aims to protect public health by regulating 

on the most sensitive and biologically plausible adverse effect. Cholinesterase

inhibition data from rat studies provides the basis for risk extrapolation for the diazinon 

(for additional information about diazinon‟s toxicity, see Appendix C).

.

Human Incidents Review of Severity and Symptoms

Taking into account the current toxicological understanding and review of the 

incident data for diazinon, the incident data is consistent with OPP‟s earlier hazard 

assessment. In this particular case study, the diazinon human incidents were identified 

from the various incident data sources, PCC, NPIC, NIOSH Sensor and PISP and the 

severity of the incidents was assessed. In PCC (using the most recent years of data, 

2004 and 2005) diazinon is in the top 10 pesticides regarding total frequency of 
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incidents reported, and in the top third regarding the proportion of severe (death, major, 

moderate) incidents. At the same time, about 95% of incidents are low severity; about 

5% of reported diazinon incidents involving one substance and one active ingredient 

resulted in a moderate, major or death classification in 2004 and 2005. 

Similar to PCC, the majority of the diazinon incidents reported in the IDS received 

low severity classifications (10% higher severity, no deaths 2004 to 2005). For NIOSH 

SENSOR, the majority of diazinon incidents fall within the low severity category; about 

7% of reported incidents in 2004 and 2005 resulted in a death or high severity 

classification. There were two cases that resulted in death, one was attributed to suicide 

by ingestion and there is no qualitative information available for the second case of 

death. Of the thirteen high severity illnesses reported, four were considered attempted 

suicides, and other incidents involved misuse. Similarly, in NPIC approximately 10% (3 

out of 28) of the incidents reported in the 2004-2005 timeframe resulted in a ”high 

severity illness or injury” classification. No deaths were reported in this database. For 

PISP, only two cases were reported in the 2004-2005 timeframe and both were 

attempted suicides. PISP does not include a severity category, but it does include the 

categories “days lost from work” and “days hospitalized” which can serve as proxies for 

a severity classification. For these two cases, only “days hospitalized” was recorded for 

one of the incidents: 8 days hospitalized, which is considered severe. 
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Figure C- 1. provides a snapshot of the types of effects reported as related to diazinon exposure 

in the 2004-2005 timeframe (the most recent two years of data available for all databases). It 

should be noted that multiple types of effects may occur concurrently within one incident. 

2004-2005 Range of Frequency of Reported Symptoms for Diazinon

0%

5%

10%

15%

20%

25%

30%

35%

40%

45%

50% Miscellaneous Dermal Neurological Ocular Gastrointestinal Respiratory Cardiovascular Muscular Renal Hematological/Hepatic

Symptom/Effect Type

Frequency of Reported Symptoms 

delta

min

NPIC

PISP

NIOSH

IDS

PCC

Frequency of Human Incidents Over Time

In addition to the review of human symptoms and severity of health outcomes, 

human incident data were also assessed to determine whether there were any trends or 

patterns over time in regions, product-types and/or exposure scenarios most likely to 

result in incidents. Because of uncertainties related to exposure inherent in incident data 

(limited information on overall usage, potential differences in reporting in 

regions/populations, uncertainty regarding the product tagged to the incident), 

conclusions cannot be made based on these analyses (see Appendix B for further 

information). Nonetheless, all human incident data point to diazinon incidents 

decreasing over time as demonstrated by Figure C-2. These decreases are in large 

measure associated with residential exposures that occurred prior to cancellation of 

residential uses in 2000, with sales of all indoor residential use products ending in 2002 

and sales of all outdoor residential use products ending in 2004.
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Figure C- 2. Diazinon incidents over time 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

CA PISP (n=154)

IDS (n=780)

NIOSH SENSOR (n=220)

NPIC (n=328)

0% PCC (n=16,642)

5%

10%

15%

20%

25%

30%

35%

40%

45%

50% % of total incidents

Year

Diazinon incidents over time

CA PISP (n=154)

IDS (n=780)

NIOSH SENSOR (n=220)

NPIC (n=328)

PCC (n=16,642)

The decline in OP and diazinon incidents has been reported on previously (Blondell 

2007; Stone 2009)

IV. CONCLUSION/SUMMARY

Overall, the review of the human incident data on diazinon largely confirms OPP‟s 

earlier hazard assessment. Most of the different types of symptoms reported following 

diazinon exposure are consistent with cholinergic toxicity, and the reports cited 

represent nearly all of the reported incidents. The databases do not suggest any new 

types of hazards.

The high frequency of “miscellaneous “effects from PISP data reflects only two 

cases with 11 reported symptoms between them, and most of the miscellaneous 

symptoms involved excessive salivation and sweating which are typical symptoms of 

cholinergic toxicity. EPA also thinks that the reported “ocular symptoms” probably reflect 

diazinon‟s cholinesterase inhibitory effects (e.g., pinpoint pupils) or local insults from 

direct exposure to the eye. Further, while dermal symptoms are somewhat unusual, 
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EPA thinks that they probably reflect local insults from direct exposure to the skin (see 

Appendix B for further details). 

In the review of incident data over time, the expected impacts of the Agency‟s 

regulatory decisions are generally reflected in the decrease of diazinon incidents over 

time across multiple human incident databases. This decrease is consistent with 

chemical use trend data (for residential and agricultural usage), as well as the four-year 

phase out/cancellation of all indoor and outdoor residential uses and the occupational 

risk mitigation actions. 

V. WEIGHING AND INTEGRATING HUMAN INCIDENT DATA INTO RISK 

ASSESSMENT AND CHARACTERIZATION

Human incident data are not collected for the explicit purpose of informing the risk 

assessment. This information, nevertheless, may serve as an important resource that 

contributes to characterizing potential risk. It also may be useful in formulating the

problem statement, in suggesting further analyses to clarify the risk potential (e.g., 

further evaluations of the toxicological database and available epidemiology studies) or

possibly to identify additional study needs. Because each incident data base source

considered by OPP and described in this report has its own strengths and weaknesses, 

the reliability and the utility of the information must be evaluated with respect to its utility 

to inform decisions on a case-by-case basis.

Incident data should be described in the context of risk characterization. For 

example, incident data may confirm experimental toxicological observations and 

biologic mechanisms, as was in the case for diazinon. In addition, such incident data 

may be useful to characterize human behavior and practices that contribute to illness 

and injury (e.g., misuse of the product). If incident data are collected for and available 

over a period of time, it may be useful to help evaluate the efficacy of previously 

implemented risk mitigation activities, as illustrated by the diazinon case study. 

When incident data are used in risk characterization, it is critical that the strengths 

and weakness of these data be properly evaluated to determine their influence on any 

conclusions and decisions regarding potential risk and the need for risk mitigation 

decisions. In weighing the evidence available in the human incident databases, a 

number of factors must be considered, including whether there is an adequate 

characterization of the nature of exposure and of the severity of the effects. Emphasis 

should be place on information of good quality and on those cases for which the effects 

are consistent or frequently observed both within and across the available databases. 

Less weight should be given to an isolated observation that is not consistent with 

broader database or to those situations that reflect only occasional obvious gross or 

intentional misuse. In the case of diazinon, the incident data base associated with this 

pesticide is strong, because the nature and frequency of effects reported were 

consistent with the broader toxicological effects observed in laboratory studies including 

its mode of action and its ability to cause cholinergic toxicity. 
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Incident data may, on occasion, identify a health effect or illness that is not 

previously observed in the toxicology studies. In some cases, these human incident 

reports may consist of anecdotal or isolated observations that have limited factual 

support or firm evidence of connection to exposure. In the case where the incident 

reports such as these are isolated, anecdotal, or have little or no support, these data 

should be given little to no weight in the integrative risk assessment process. In those 

cases where a greater number of reports are seen and there is some biological 

plausibility connected to the effect or illness, further broader analyses or investigations 

should be considered to help clarify or confirm the findings. 

.
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APPENDIX A: CHEMICAL USE TRENDS

The usage data in this report is from two sources. The first source reports the chemical 

usage for non-agricultural sites and the data are collected via survey by a private 

market research firm. The second data source is the California Department of Pesticide 

Regulation and the data are gathered under the full use reporting required of all 

agricultural pesticide uses (which includes structural fumigation, pest control, and turf 

applications) in the state. The available usage data sets are grouped into two 

categories, consumer and professional usage, in order to provide context to the different 

incident data sets. 

Consumer (Homeowner) Usage

The data reported below provides an estimate of the pounds of diazinon applied by 

consumers on outdoor sites. 

(EPA Proprietary Data-approved for public release)

The increase in diazinon usage between 1997 and 2001 is likely due to the phase-out of 

another organophosphate, chlorpyrifos. The phase-out of chlorpyrifos left diazinon as 

the market leader. In 2000, there was a cancellation of all residential uses of diazinon 

and retail sales of the products ended by the end of 2004. Therefore, the decrease in 

diazinon usage between 2001 and 2005 is likely a reflection of the product availability. 

Professional Usage

Pest Management Professional (PMP) Firms: There are limited data to report for the 

pounds of diazinon applied by (PMP) firms. PMP applicators primarily treat areas in 

and around buildings for pests such as: termites, cockroaches, fleas, ants, and other 

pests. These applications are made to both residential and commercial establishments 

and nearly 70 % of the applications are in residential establishments. 
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The available data from 2001 and 2003 shows a decline in the total number of pounds 

applied from 430,000 to 110,000 (EPA Proprietary Data-Approved for public release). 

While these data are limited, it is likely that the pounds of diazinon applied by PMP firms 

have been declining since the cancellation of residential uses in 2000. 

Professional Turf and Ornamental Pesticide Applicators: The data reported below 

provide an estimate of the pounds of diazinon applied by professional turf and 

ornamental applicators. This data set covers the following sectors: golf courses, lawn 

care operators, horticultural nurseries and greenhouses, institutional turf facilities, 

landscape contractors, and turf farms. The lawn care operators and landscape 

contractors apply pesticides to residential and nonresidential areas. 

(EPA Proprietary Data-Approved for public release)

In 1988, there was a cancellation of outdoor uses on golf courses and sod farms and in 

2000 there was a cancellation of residential uses. 

Professional Usage of Diazinon in California (Agricultural and Non-Agricultural): The 

data reported below represents the pounds of Diazinon applied on all sites in California 

except home and garden applications and most industrial and institutional uses. 
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(CALDPR, 1997-2007)

The California data reflect a smoother decline over the years, likely because this data 

set does not include home and garden applications which were cancelled in 2000. The 

decline in 2002, is likely to be due to the agricultural mitigation measures required in the 

2002 IRED. 

Diazinon usage appears to be decreasing over time in both non-agricultural and 

agricultural sectors. The decline in residential usage accords well with the four-year 

phase out/cancellation of all indoor and outdoor residential uses beginning in the year 

2002 (effective December 31, 2002, retailers could no longer sell indoor residential 

products; effective December 31, 2004, retailers could no longer sell outdoor residential 

products). The decline in agricultural usage (as indicated by California data) also 

accords well with risk mitigation measures impacting agricultural workers (specified in 

the 2002 IRED). Although as depicted below (and as expected), agricultural usage is 

not declining as rapidly as non-agricultural usage.

Diazinon Usage in California

0

200

400

600

800

1000

1200

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year Reported

Lbs AI Applied x1000

AG 

Non-AG
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APPENDIX B: HUMAN INCIDENT DATA – ADDITIONAL ANALYSES/INFORMATION

More detailed incident analyses are captured in this appendix (as well as details of 

some of the figures/numbers presented in the body of the document). While not all 

were considered sufficiently relevant to mention in the body of this case study they are 

presented here for completeness and transparency.

Figure 1 depicts the frequency of reported symptoms across the databases, and the 

table below provides the information that informed the figure.

Table B.1 Frequency of Reported Symptoms 2004-2005

Effect Type PCC IDS NIOSH 

SENSOR PISP NPIC

Cardiovascular 4% 2% 10% 9% 7% 

Dermal 14% 35% 8% 13%

Gastrointestinal 18% 20% 21% 9% 18%

Hematological/Hepatic 0% 9%

Neurological 13% 15% 31% 9% 27%

Ocular 29% 3% 15% 9% 18%

Renal 0% 3% 2%

Respiratory 6% 19% 8% 18% 9%

Muscular 6%

Miscellaneous 15% 5% 36% 7%

Total Reported 

Symptoms 854 65 39 11 99

Total Incidents* 2028 52 17 2 28

*involving one substance, one active ingredient

Hatched cells indicate these categories were not available in particular database, empty cells indicate no 

symptoms fell into these categories.

One way incidents have been used in post-market surveillance is to discern whether 

there are particular products within a similar group of products that stand out as 

resulting in more and/or more severe incidents than others in the same group or if there 

is a particular geographic pattern of incidents. The following tables depict initial 

explorations into these two potential patterns/trends. IDS and PCC are the preferred 

databases to look for trends in product frequencies/geography due to the high number 

of reported incidents and national coverage, with the caveat that the Agency has less 

confidence in the product information in PCC. If a pattern/trend emerges, other 

databases are consulted. For diazinon, our analysis was aborted due to lack of 

discerned pattern/trends upon initial review.
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Table B.2 Product Frequency – Diazinon Incidents – frequency by product (initial attempt)

PCC Product Name

EPA 

Reg. 

Number

PCC

1993-

2005

NPIC

1995-2001

NPIC

2002-2008

IDS

2000-2007

(EPA Reg. 

No.)

NIOSH 

SENSOR

DIAZINON 20964

(12%)

Diazinon

ORTHO DIAZINON 

PLUS INSECT 

SPRAY from 

CHEVRON 

(INSECTICIDE)

1081 

(5.7%)

Ortho 

Diazinon 

Plus Insect 

Spray

2390264

3

Diazinon 

Ultra Insect 

Spray

Spectracide

Diazinon 

4EC

KGRO 

Diazinon 

Insect 

Spray

Dexol And 

& Roach 

Killer

Diazinon 

Granules 

KGRO

SA-50 

Diazinon 

Spray 

Concentrate

Diazinon 

Lawn & 

Garden 

Insecticide

Super KGRO 

Fruit & 

Vegetable 

Insect

SPECTRACIDE FIRE 

ANT KILLER 

GRANULES from 

SPECTRUM GROUP

0088450

0101

964

ORTHO DIAZINON 

INSECT SPRAY from 

SOLARIS GROUP

0002390

2364

584 

(6.2%)

Ortho 

Diazinon 

Insect Spray

Diazinon 

Plus Insect 

Spray 

Concentrate

ORTHO 

DIAZINON 

INSECT 

SPRAY

*Product name not provided in CA PISP database
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Table B.3 Diazinon Incidents – frequency by state (‘bold font’ for top states for each database)

PCC IDS NIOSH SENSOR NPIC

State Incident 

Count Percent 

Number Of 

Cases

Incident 

count

% top 12 

states

AK 8 0%

AL 875 2% 1 Most incidents

AR 964 3% 5

AZ 843 2% 6 90 1% Incidents occurred

CA 4831 14% 65 1134 19% Incidents occurred

CO 591 2% 4 3

CT 270 1% 2

DC 54 0%

DE 47 0% 1

FL 2552 7% 32 816 13% Most incidents

GA 1580 5% 12

HI 35 0%

IA 275 1% 4 37 1%

ID 455 1% 2 Incidents occurred

IL 472 1% 16 1

IN 763 2% 11

KS 241 1% 2

KY 568 2% 5 1 Most incidents

LA 624 2% 6 851 14% Most incidents

MA 518 1% 8

MD 385 1% 3

ME 4

MI 1258 4% 10 336 5%

MN 249 1% 5

MO 893 3% 18

MS 166 0% 5 1

MT 116 0% 2

NC 929 3% 17 1 Most incidents

ND 18 0%

NE 362 1% 1

NH 180 1% 1

NJ 442 1% 5 1

NM 507 1% 4 18 0%

NV 316 1% 3

NY 911 3% 10 581 9%

OH 891 3% 10 2

OK 625 2% 8

OR 633 2% 7 356 6%

PA 878 3% 8

RI 91 0% 1

SC 189 1% 6

SD 70 0% 2

TN 692 2% 12

TX 3875 11% 39 1440 24% Most incidents

UT 977 3% 9

VA 785 2% 11 1

VT 19 0%

WA 1298 4% 14 513 8% Incidents occurred

WI 324 1% 5

WV 190 1% 6

WY 82 0% 1
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Unknown 59 0% 1

Refused to give 11 0%

Other US territory 1 0%

Overseas US military 1 0%

Mexico 38 0% 4 0%

Foreign country (not 

MX or CN) 3 0%

Out Of Country 4

Total 414

PCC

PCC is one of the easier incident databases to work with. To assess whether incidents 

involving children and adults result in different symptom profiles, the data were

segregated by age group. AAPCC incident information does not indicate that diazinon 

is more toxic to children than „adults‟ (people older than 12 years old). Additionally, the 

clinical effects most frequently reported are similar in both age categories, as are the 

proportion of reported clinical effects. 

Figure B.1

DURATION AGE No. of 

incident

s

SEVERITY Reported CLINICAL EFFECTS

All durations < 12 

years

4032 

(12%)

1% high severity (moderate, major, 

death)

(code) Medical 

outcome Count %

(4)Death 1 0%

(3)Major effect 11 0%

(2)Moderate 

effect 56 1%

(1)Minor effect 312 8%

(6)Not followed 

(judged at 

most minor) 837 21%

(0)No effect 1817 45%

(5)Not followed 

(judged 

nontoxic) 545 14%

(7)Unable to 

follow 

(potentially 

toxic) 91 2%

(8)Unrelated 

effect 362 9%

Reported clinical effects (<12 years old)

3% 13%

31%

14% 0%

17%

0%

10%

12%

CARDIO DERMAL GASTRO HEMEHEP NEURO

OCULAR RENAL RESP MISC

*Clinical effects for medical outcomes coded 

1,2,3,4,6,7,10

*Most frequently reported clinical effects = 

1gastrointestinal/vomiting, 2ocular/irritation,pain; 

3miscellaneous/other; 4respiratory/cough,choke
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> 12 

years

30998 

(88%)

6% high severity (moderate, major, 

death)

Medical 

outcome Count %

(4)Death 12 0%

(10)Death -

indirect report 2 0%

(3)Major effect 179 1%

(2)Moderate 

effect 1663 5%

(1)Minor effect 6492 21%

(6)Not followed 

(judged at 

most minor) 7589 24%

(0)No effect 6314 20%

(5)Not followed 

(judged 

nontoxic) 2166 7%

(7)Unable to 

follow 

(potentially 

toxic) 1415 5%

(8)Unrelated 

effect 5166 17%

Reported clinical effects (>12 years old)

3% 14%

30%

17% 0%

17%

0%

7%

12%

CARDIO DERMAL GASTRO HEMEHEP NEURO

OCULAR RENAL RESP MISC

*Clinical effects for medical outcomes coded 

1,2,3,4,6,7,10

*Most frequently reported clinical effects = 

1ocular/irritation,pain; 2gastrointestinal/nausea; 

3gastrointestinal/vomiting

Figure B.2 Adults/People > 12 years old

Exposure Site

Number of 

associated 

incidents Percentage

Own_residence 27399 88%

Workplace 1606 5%

Other_residence 1221 4%

Public_Area 309 1%

Unknown 231 1%

Other 117 0%

School 66 0%

Health_care_facility 41 0%

Restaurant/food_service 8 0%

Figure B.3 Children/People < 12 years old

Exposure Site

Number of 

associated 

incidents Percentage

Own_residence 3727 92%

Other_residence 246 6%

Public_Area 29 1%

School 9 0%

Unknown 8 0%

Other 7 0%

Workplace 3 0%

Health_care_facility 2 0%

Restaurant/food_service 1 0%
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The sites of exposure are not that different between these two age categories, except 

the older category includes exposure in the workplace. 

Considering the proportion of severe outcomes in relation to all incidents is a potential 

metric for classifying the hazard potential for pesticides. Although diazinon incidents 

are declining over time, of note is a fairly steady proportion of severe outcomes (~6%). 

The incidents tallied below may involve more than one substance and/or active 

ingredient (although over 90% involve just one substance and one active ingredient).

Figure B.4

AAPCC: Diazinon incidents over time

6%

5% 6% 6% 5% 6% 6% 6% 6% 5%

7%

5%

5%

0

500

1000

1500

2000

2500

3000

3500

1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year

Incidents

non-severe medical outcome (codes 0,1,5,6,7,8) severe outcomes (codes 2,3,4 or 10) percent

NIOSH SENSOR

The 220 diazinon cases are grouped by severity in Table B.4 below. As can be seen, 

the majority of these cases fell within the low severity category, and a total of 15 cases 

fell within the death or high severity category.

Table B.4 Number of Cases by Severity of Outcome

Severity of Outcome Number of Cases

Death 2

High severity illness or injury 13

Moderate severity illness or injury 53

Low severity illness or injury 152

For the two cases resulting in death, one was attributed to suicide by ingestion. For the 

second case there is no qualitative information available on the behavior surrounding 

the fatal exposure.

Of the thirteen high severity illnesses reported, four were considered attempted 

suicides. Another case was noted as an accidental ingestion. In a sixth case, a woman 
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applied diazinon on her skin as a treatment for scabies. A seventh case resulted from 

mixing and spraying the pesticide in bathroom. An eight case resulted from mixing the 

chemical with kerosene and spraying it in a home. A ninth case involved exposure in a 

well ventilated utility room. It was not possible to identify the type of exposure for the 

remaining cases.

In Table B.5, the type and number of reported symptoms for each category of outcome 

severity are shown. In the case of death, respiratory, GI, and neurological symptoms 

were reported. In those cases classified as high severity, cardiovascular, respiratory, 

GI, and neurological symptoms were most the frequently indicated symptoms. For the 

moderate and low severity categories, GI, neurological and respiratory symptoms were 

the most common.

Table B.5 Types of Symptoms Associated with each Outcome Severity Category

Outcome

Dermal Cardio Resp GI

Rena

l

Neur

o Eye Misc

Death 0 0 1 1 0 1 0 0

High severity illness or injury 1 10 9 10 4 11 6 5

Moderate severity illness or injury 10 12 20 33 3 39 8 12

Low severity illness or injury 41 13 59 80 5 90 36 21

For children under the age of six there were eleven total reported incidents. There was 

a single high severity case where dermal, respiratory, GI, neurological and eye related 

symptoms were reported. For the remaining cases, GI and neurological symptoms 

were the most frequently reported symptoms.

Table B.6 Children Under 6, Types of Symptoms Associated with each Outcome 

Severity Category

Outcome Dermal Cardio Resp GI

Rena

l

Neur

o Eye Misc

High severity illness or injury 1 0 1 1 0 1 1 0

Moderate severity illness or injury 0 1 2 2 0 2 1 1

Low severity illness or injury 2 1 0 4 0 3 0 2

CA PISP

Among the case reports between 1996 and 2006, the majority of the reported symptoms 

involved systemic effects such as nausea, vomiting, dizziness, diarrhea, tingling, 

tachycardia, weakness, headache, chest pain, sweating, lightheadedness, numbness 

and bradycardia. A large number of these exposures occurred from non-occupational 

exposure to drift. During school hours, a groundskeeper used a hose-end sprayer to 

apply diazinon to shrubbery about 15 feet from the air conditioner intake. The odor 

entered the ventilation system in the first floor classrooms. About 15 minutes later, 

several students reported symptoms including headache and visited the school nurse. 

Most of the students requested to go home after being evaluated.
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Figure B.5

Diazinon Incidents in California

0

10

20

30

40

50

60

70

80

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year

Number of incidents

AG

Non-AG
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APPENDIX C: ADDITIONAL TOXICOLOGICAL INFORMATION

The mechanism of toxicity for diazinon is typical of an anticholinesterase 

organophosphate that inhibits acetylcholinesterase (AChE) in the central and peripheral 

nervous system. AChE is responsible for terminating the action of the neurotransmitter, 

acetylcholine in the synapse of the pre- and postsynaptic nerve endings and in the 

neuromuscular junction. The action of acetylcholine does not persist long as it is 

hydrolyzed by AChE and rapidly removed. As an anticholinesterase organophosphate, 

diazinon inhibits AChE by reacting with the active site to form a stable phosphorylated 

complex incapable of deactivating acetylcholine at the synaptic gutter between the preand postsynaptic nerve endings or neuromuscular junctions of skeletal muscles 

resulting in accumulation of acetylcholine at these sites. This leads to continuous or 

excessive stimulation of cholinergic fibers in the postganglionic parasympathetic nerve 

endings, neuromuscular junctions of the skeletal muscles, and cells of the central 

nervous system that results in hyperpolarization and receptor desensitization. These 

cholinergic actions involving end organs (heart, blood vessels, secretory glands) 

innervated by fibers in the postganglionic parasympathetic nerves result in muscarinic 

effects, which are manifested as miosis, excessive glandular secretions (salivation, 

lacrimation, rhinitis), nausea, urinary incontinence, vomiting, abdominal pain, diarrhea, 

bronchoconstriction or bronchospasm, increased bronchosecretion, vasodilation, 

bradycardia, and hypotension. Nicotinic effects are due to accumulation of acetylcholine 

at the skeletal muscle junctions and sympathetic preganglionic nerve endings. Nicotinic 

effects are manifested as muscular fasciculations, weakness, mydriasis, tachycardia, 

and hypertension. The central nervous system effects are due to accumulation of 

acetylcholine at various cortical, subcortical, and spinal levels (primarily in the cerebral 

cortex, hippocampus, and extrapyramidal motor system). The central nervous system 

effects are manifested as respiratory depression, anxiety, insomnia, headache, 

restlessness, tension, mental confusion, loss of concentration, apathy, drowsiness, 

ataxia, tremor, convulsion, and coma (ATSDR, 2008).
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REFERENCES1

40 CFR §159.184

Agency for Toxic Substances and Disease Registry (ATSDR). 2008. Toxicological 

profile for Diazinon. Atlanta, GA: U.S. Department of Health and Human Services, 

Public Health Service. 

Blondell, JM, 2007. “Decline in pesticide poisonings in the United States from 1995 to 

2004.” Clinical Toxicology, 45:5, 589-592.

Calvert, GM, Barnett, M, Blondell JM, Mehler, LN, Sanderson, WT. “Surveillance of 

Pesticide-Related Illness and Injury in Humans” Handbook of Pesticide Toxicology, 2nd

ed. Ed. R. Krieger, Ed. Academic Press: San Diego, 2001.

Environmental Protection Agency (EPA), Reigart, JR, Roberts, JR. 1999. Recognition 

and Management of Pesticide Poisonings, Fifth Edition. EPA 735-R-98-003. March 

1999.

http://www.epa.gov/oppfead1/safety/healthcare/handbook/handbook.htm

Environmental Protection Agency (EPA), 2004. Interim Reregistration Eligibility Decision 

for Diazinon. EPA 738-R-04-006. May 2004.

http://www.epa.gov/oppsrrd1/reregistration/REDs/diazinon_red.pdf

Environmental Protection Agency (EPA), 2008. Diazinon. Revised Human Health 

Assessment Scoping Document in Support of Registration Review. EPA-HQ-OPP2008-0351-002. June 2008.

http://www.regulations.gov/search/Regs/home.html#documentDetail?R=090000648060

e907

Hoffman, RS, 2007. “Understanding the limitations of retrospective analyses of poison 

center data.” Clinical Toxicology (2007) 45, 943–945.

Stone, DL, Sudakin, DL, Jenkins, JJ 2009. “Longitudinal trends in organophosphate 

incidents reported to the National Pesticide Information Center, 1995-2007.” 

Environmental Health 2009, 8:18.

http://www.ehjournal.net/content/8/1/18

World Health Organization/International Programme on Chemical Safety (WHO/IPCS), 

2002. Report of the Meeting on Bridging the Gap Between Clinical and Regulatory 

Toxicology. January 2002. 

http://www.who.int/ipcs/methods/en/bridging_gap_report.pdf

 

1 References have not been consistently cited in the document, and will be amended before the SAP.
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Page 27 of 27

World Health Organization/International Programme on Chemical Safety (WHO/IPCS), 

2004. Report: Workshop on Poisons Centres and the Use of Human Data in Consumer 

Product Risk Assessment. May 2005. 

http://www.who.int/ipcs/methods/en/cardiff_report.pdf