Ames, pesticides, and cancer revisited

The case for continuing use of existing levels of pesticides in agriculture, espoused by Bruce Ames, is refuted. Ames' contentions that naturally occurring carcinogens are far more widespread than man-made ones, that pesticides prevent cancer by providing fruits and vegetables at lower costs to the poor, and that animal data on high risks with high doses cannot predict low risks from low doses in humans do not address key issues: 1) fruits and vegetables contain mixtures of carcinogens and anti-carcinogens, and selection effects from human exposures to these mixtures go back more than a million years; 2) exposures from bioconcentrations of biopersistent organochlorines in the food chain create particular risks for meat-eaters, who have higher cancer risks than vegetarians; 3) even low doses from ingestion of produce containing pesticide residues can cause tissue injury, which could itself promote cancer; 4) epidemiologic data show rises in cancer incidences in older people in many countries, major differences in cancer risks between countries, and converging trends in risks for populations migrating to certain countries; 5) studies of pesticide-exposed workers consistently show increased rates of cancers and birth defects and cancers in their offspring; 6) epidemiologic studies based on large databases tend to underestimate risks from environmental causes because of exposure misclassification; 7) exposures to many organochlorines may have pervasive effects on endocrine function; 8) crop yields can be increased with less use of pesticides. Studies demonstrating the latter need replication, and should be supported as part of a coherent government agenda to develop alternative farming methods.     

Assessing aggregate and cumulative pesticide risks using a probabilistic model

Determining aggregate and cumulative risks from exposures to pesticides presents a number of challenges. The analysis must capture the correlations in residues that occur from both additive and exclusionary processes in the use of pesticides. The analysis also requires a quantitative mechanism for evaluating risks associated with exposures to mixtures of pesticides. This paper presents an analysis of aggregate exposures and risks associated with exposures to a pesticide, Alpha, and the cumulative exposure to and risk from three pesticides, Alpha, Beta, and Gamma. The cumulative risks are evaluated by determining the systemic (absorbed) doses that result from inhalation, dermal, and oral exposures to the pesticides. A 'relative toxicity' model is used to evaluate cumulative risks. The assessment of cumulative exposure was performed using the LifeLine Version 1.0. The model simulates pesticide exposure using an individual-based approach where daily exposures are evaluated for each person, season, and location.     

Occupational exposure to magnetic fields in relation to mortality from brain cancer among electricity generation and transmission workers.

OBJECTIVE: To investigate whether the risks of mortality from brain cancer are related to occupational exposure to magnetic fields. METHODS: A total of 112 cases of primary brain cancer (1972-91) were identified from a cohort of 84,018 male and female employees of the (then) Central Electricity Generating Board and its privatised successor companies. Individual cumulative occupational exposures to magnetic fields were estimated by linking available computerised job history data with magnetic field measurements collected over 675 person-workshifts. Estimated exposure histories of the case workers were compared with those of 654 control workers drawn from the cohort (nested case-control study), by means of conditional logistic regression. RESULTS: For exposure assessments based on arithmetic means, the risk of mortality from brain cancer for subjects with an estimated cumulative exposure to magnetic fields of 5.4-13.4 microT.y v subjects with lower exposures (0.0-5.3 microT.y) was 1.04 (95% confidence interval (95% CI) 0.60 to 1.80). The corresponding relative risk in subjects with higher exposures (> or = 13.5 microT.y) was 0.95 (95% CI 0.54 to 1.69). There was no indication of a positive trend for cumulative exposure and risk of mortality from brain cancer either when the analysis used exposure assessments based on geometric means or when the analysis was restricted to exposures received within five years of the case diagnosis (or corresponding period for controls). CONCLUSIONS: Although the exposure categorisation was based solely on recent observations, the study findings do not support the hypothesis that the risk of brain cancer is associated with occupational exposure to magnetic fields.     

Occupational exposures to influenza among healthcare workers in the United States

The objective of this study is to estimate the annual number of occupational exposures to influenza among healthcare workers that result from providing direct and supportive care to influenza patients in acute care, home care and long-term care settings. Literature review was used to identify healthcare utilization for influenza, and worker activity patterns. This information was used, with Monte Carlo simulation, to tabulate the mean annual number of occupational exposures. Given a medium-sized epidemic with a 6% annual symptomatic influenza incidence proportion, the mean number of occupational exposures was estimated to be 81.8 million annually. Among the approximately 14 million healthcare workers, this corresponds to 5.8 exposures per worker annually, on average. Exposures, however, are likely concentrated among subsets of healthcare workers. Occupational exposures were most numerous in ambulatory care settings (38%), followed by long-term care facilities (30%) and home care settings (21%). The annual number of occupational exposures to influenza is high, but not every occupational exposure will result in infection. Some infection control activities, like patient isolation, can reduce the number of occupational exposures.     

Pesticide exposures, cholinesterase depression, and symptoms among North Carolina migrant farmworkers.

OBJECTIVES. We conducted a clinic-based study of erythrocyte cholinesterase levels, pesticide exposures, and health effects among farmworkers and nonfarmworkers to determine risks for exposure and associated morbidity. METHODS. Two hundred two farmworkers and 42 nonfarmworkers were recruited sequentially at two community health centers. Erythrocyte cholinesterase levels were measured colorimetrically. Questionnaires obtained data on demographics, occupational history, exposures, and symptoms. RESULTS. Cholinesterase levels were significantly lower among farmworkers (30.28 U/g hemoglobin) than among nonfarmworkers (32.3 U/g hemoglobin). Twelve percent of farmworkers, but no nonfarmworkers, had very low levels. Farmworkers applying pesticides also had lower cholinesterase levels. One half of farmworkers reported being sprayed by pesticides and working in fields with an obvious chemical smell. Of reported symptoms, only diarrhea was associated with cholinesterase levels. Reported exposures, however, were strongly associated with symptoms. CONCLUSIONS. Farmworkers reported many pesticide exposures that violate state and federal regulations. Farmworkers had cholinesterase levels significantly lower than those of nonfarmworkers, although only spraying pesticides was associated with very low levels.     

A screening-level assessment of the health risks of chronic smoke exposure for wildland firefighters

A screening health risk assessment was performed to assess the upper-bound risks of cancer and noncancer adverse health effects among wildland firefighters performing wildfire suppression and prescribed burn management. Of the hundreds of chemicals in wildland fire smoke, we identified 15 substances of potential concern from the standpoints of concentration and toxicology; these included aldehydes, polycyclic aromatic hydrocarbons, carbon monoxide, benzene, and respirable particulate matter. Data defining daily exposures to smoke at prescribed burns and wildfires, potential days of exposure in a year, and career lengths were used to estimate average and reasonable maximum career inhalation exposures to these substances. Of the 15 substances in smoke that were evaluated, only benzene and formaldehyde posed a cancer risk greater than 1 per million, while only acrolein and respirable particulate matter exposures resulted in hazard indices greater than 1.0. The estimated upper-bound cancer risks ranged from 1.4 to 220 excess cancers per million, and noncancer hazard indices ranged from 9 to 360, depending on the exposure group. These values only indicate the likelihood of adverse health effects, not whether they will or will not occur. The risk assessment process narrows the field of substances that deserve further assessment, and the hazards identified by risk assessment generally agree with those identified as a concern in occupational exposure assessments.     

Sources of exposure to and public health implications of organophosphate pesticides.

OBJECTIVE: To review the public health significance of organophosphate pesticide exposure in the United States of America. Since the situation of high organophosphate pesticide exposure and the concomitant health risks in the developing countries of the world is well known, this article seeks to highlight the public health significance of organophosphate exposure in the United States, where it is less common than in many other nations. Looking at the situation in the United States would serve to further emphasize the seriousness of organophosphate pesticide-related health issues in developing countries. METHODS: A search for journal articles on organophosphate pesticides and organophosphate exposure was done on the PubMed electronic bibliographic database system of the National Library of Medicine of the United States. To supplement that search, information on organophosphate toxicity, biological monitoring, and regulation of pesticides was obtained from other published articles, textbooks, and relevant Internet sites. RESULTS: Organophosphate pesticides are a group of chemicals that are mainly used in agriculture. Organophosphates inhibit the activity of both the cholinesterase (ChE) enzymes-red blood cell (RBC) ChE and serum ChE-resulting in the cholinergic features of organophosphate toxicity. A 50% reduction in serum ChE activity from the baseline is an indication of acute organophosphate toxicity. The RBC ChE activity, which is less rapidly depressed than the serum ChE activity, is a measure of chronic exposure to organophosphates. Exposures to organophosphates are broadly classified into two categories: occupational and environmental. Occupational exposures occur among agricultural workers (including migrant farmworkers), industrial workers, pest control exterminators, and other workers. Nonoccupational exposure affects a large segment of the general population in the United States. Residential exposures come from organophosphate pesticide use by exterminators and by household residents as well as from dietary and accidental exposures. Other environmental exposures occur in public places and areas close to farms, and exposures could also happen from organophosphate use in chemical warfare or terrorism. In the United States some organophosphate pesticides are restricted by the Environmental Protection Agency in order to protect humans, animals, and the environment. In addition, the Food Quality Protection Act regulates dietary exposure to pesticides, particularly for infants and children. CONCLUSIONS: Organophosphate pesticides continue to pose a risk to human health in the United States. Biological monitoring should be used to strictly regulate occupational exposures to organophosphates and thus protect the health and safety of workers. Among the public there should be an increased awareness of environmental exposure to organophosphates as well as of the threat of chemical warfare or terrorism.     

Systematic Review and Meta-analysis of Circulatory Disease from Exposure to Low-Level Ionizing Radiation and Estimates of Potential Population Mortality Risks

Background: Although high doses of ionizing radiation have long been linked to circulatory disease, evidence for an association at lower exposures remains controversial. However, recent analyses suggest excess relative risks at occupational exposure levels.Objectives: We performed a systematic review and meta-analysis to summarize information on circulatory disease risks associated with moderate- and low-level whole-body ionizing radiation exposures.Methods: We conducted PubMed/ISI Thomson searches of peer-reviewed papers published since 1990 using the terms “radiation” AND “heart” AND “disease,” OR “radiation” AND “stroke,” OR “radiation” AND “circulatory” AND “disease.” Radiation exposures had to be whole-body, with a cumulative mean dose of < 0.5 Sv, or at a low dose rate (< 10 mSv/day). We estimated population risks of circulatory disease from low-level radiation exposure using excess relative risk estimates from this meta-analysis and current mortality rates for nine major developed countries.Results: Estimated excess population risks for all circulatory diseases combined ranged from 2.5%/Sv [95% confidence interval (CI): 0.8, 4.2] for France to 8.5%/Sv (95% CI: 4.0, 13.0) for Russia.Conclusions: Our review supports an association between circulatory disease mortality and low and moderate doses of ionizing radiation. Our analysis was limited by heterogeneity among studies (particularly for noncardiac end points), the possibility of uncontrolled confounding in some occupational groups by lifestyle factors, and higher dose groups (> 0.5 Sv) generally driving the observed trends. If confirmed, our findings suggest that overall radiation-related mortality is about twice that currently estimated based on estimates for cancer end points alone (which range from 4.2% to 5.6%/Sv for these populations).     

Community exposures to airborne agricultural pesticides in California: ranking of inhalation risks

We assessed inhalation risks to California communities from airborne agricultural pesticides by probability distribution analysis using ambient air data provided by the California Air Resources Board and the California Department of Pesticide Regulation. The pesticides evaluated include chloropicrin, chlorothalonil, chlorpyrifos, S,S,S-tributyl phosphorotrithioate, diazinon, 1,3-dichloropropene, dichlorvos (naled breakdown product), endosulfan, eptam, methidathion, methyl bromide, methyl isothiocyanate (MITC; metam sodium breakdown product), molinate, propargite, and simazine. Risks were estimated for the median and 75th and 95th percentiles of probability (50, 25, and 5% of the exposed populations). Exposure estimates greater than or equal to noncancer reference values occurred for 50% of the exposed populations (adults and children) for MITC subchronic and chronic exposures, methyl bromide subchronic exposures (year 2000 monitoring), and 1,3-dichloropropene subchronic exposures (1990 monitoring). Short-term chlorpyrifos exposure estimates exceeded the acute reference value for 50% of children (not adults) in the exposed population. Noncancer risks were uniformly higher for children due to a proportionately greater inhalation rate-to-body weight ratio compared to adults and other factors. Target health effects of potential concern for these exposures include neurologic effects (methyl bromide and chlorpyrifos) and respiratory effects (1,3-dichloropropene and MITC). The lowest noncancer risks occurred for simazine and chlorothalonil. Lifetime cancer risks of one-in-a-million or greater were estimated for 50% of the exposed population for 1,3-dichloropropene (1990 monitoring) and 25% of the exposed populations for methidathion and molinate. Pesticide vapor pressure was found to be a better predictor of inhalation risk compared to other methods of ranking pesticides as potential toxic air contaminants.     

Household and occupational exposure to pesticides and risk of breast cancer

The association between breast cancer in women and the use of household or occupational pesticides was examined in a population-based case-control study. This study was conducted in Western Australia in 2009–2011and included 1,789 controls and 1,205 cases. Information on household pesticide exposure was collected from questionnaires. For occupational pesticide exposure, job-specific modules (JSMs) were used. To evaluate potential recall bias, we stratified the analysis by belief about whether pesticides contribute to breast cancer. Unconditional logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Women’s exposures to pesticides in households and workplaces were not related to increased risk of breast cancer (OR?=?1.10; CI: 0.86–1.37) and (OR?=?0.77; CI: 0.45–1.32), respectively. The prevalence of occupational exposure to pesticides among women in our study was low. In the stratified analyses, the odd ratios associated with household pesticide use were similar among participants who believed pesticides increased breast cancer risk and those who did not. The results of our study did not show associations between breast cancer and household or occupational exposure to pesticides.     

The Agricultural Health Study.

The Agricultural Health Study, a large prospective cohort study has been initiated in North Carolina and Iowa. The objectives of this study are to: 1) identify and quantify cancer risks among men, women, whites, and minorities associated with direct exposure to pesticides and other agricultural agents; 2) evaluate noncancer health risks including neurotoxicity reproductive effects, immunologic effects, nonmalignant respiratory disease, kidney disease, and growth and development among children; 3) evaluate disease risks among spouses and children of farmers that may arise from direct contact with pesticides and agricultural chemicals used in the home lawns and gardens, and from indirect contact, such as spray drift, laundering work clothes, or contaminated food or water; 4) assess current and past occupational and nonoccupational agricultural exposures using periodic interviews and environmental and biologic monitoring; 5) study the relationship between agricultural exposures, biomarkers of exposure, biologic effect, and genetic susceptibility factors relevant to carcinogenesis; and 6) identify and quantify cancer and other disease risks associated with lifestyle factors such as diet, cooking practices, physical activity, smoking and alcohol consumption, and hair dye use. In the first year of a 3-year enrollment period, 26,235 people have been enrolled in the study, including 19,776 registered pesticide applicators and 6,459 spouses of registered farmer applicators. It is estimated that when the total cohort is assembled in 1997 it will include approximately 75,000 adult study subjects. Farmers, the largest group of registered pesticide applicators comprise 77% of the target population enrolled in the study. This experience compares favorably with enrollment rates of previous prospective studies.     

Pesticide use among farmers in the Amazon basin of Ecuador

Pesticide use is one of the most significant occupational exposures for agricultural workers in the Amazon basin of Ecuador. A structured questionnaire was developed focusing on sociodemographic characteristics, knowledge and experience of adverse health effects related to pesticide use, details of work practices, and an inventory of pesticides used on the farm. Of the 112 farmers interviewed, 111 (99.1%) used pesticides. Paraquat was most commonly used (77.4%), followed by glyphosate (65.7%). Respondents had good knowledge about the acute health effects of pesticides and their exposure routes. Risk behaviors were identified as frequent pesticide use, washing pesticide equipment in water sources used by humans, inadequate disposal of empty pesticide containers, eating and drinking during pesticide application, and using inadequate protective clothing. Training and educational campaigns on pesticide use should be encouraged for this cohort, along with suggestions for alternative methods of pest control.     

Influence of socioeconomic factors on the pesticides poisoning, Brazil

OBJECTIVE: The indiscriminate use of pesticides has been contributing for the environmental quality degradation, as well as it increases the occupational exposures to these products, determining a serious public health problem in rural areas. The purpose of this study was to evaluate the exposures of rural workers of Rio de Janeiro State to anticholinesterasic pesticides, through the analyses of the acetylcholinesterase from red cells (AChE) and plasmatic butyrilcholinesterase (BChE) levels. Social-economic factors, such as the educational level of these workers, can strongly influence this situation, reason why the impact of some social-economic indicators and practices of pesticides' use in the human contamination status for rural areas were also evaluated. METHODS: The evaluation of rural workers exposure to pesticides was performed to a random sample of 55 workers among the 300 inhabitants of the study area - five communities of Magé county, RJ. The AChE and BChE activities were determined to these workers. The enzymatic activities were evaluated according to the Ellman's method modified by Oliveira-Silva. Social-economic and pesticides use data were collected by a structured interview. The possible role of social-economic and pesticide use indicators as determinants of the worker's contamination was estimated by multivariate statistic techniques, using the enzymatic activity as the dependent variable and the social-economics pesticides use indicators as independent variables. RESULTS AND CONCLUSIONS: The data showed distinct results concerning the incidence of excessive exposure, according to the enzymatic indicator used. In the studied sample, a result of 3.0 % was found for the BChE values, and 41.8 %, according to AChE. Individuals with at least one positive enzymatic indicator result were considered as "intoxicated". When these data were compared to the social-economic and pesticides use factors, it was showed the importance of educational level in the prevalence of intoxication. The others indicators studied did not showed any significant and evident correlation.     

Operative modalities and exposure to pesticides during open field treatments among a group of agricultural subcontractors

This paper reports the results of a field study of occupational pesticide exposure (respiratory and dermal) among a group of Italian agricultural subcontractors. These workers consistently use pesticides during much of the year, thus resulting in a high exposure risk. Ten complete treatments were monitored during spring/summer. Pesticides that were applied included azinphos-methyl, dicamba, dimethoate, terbuthylazine, and alachlor. Several observations were made on worker operative modalities and the use of personal protective equipment (PPE) during work. Total potential and actual exposure ranged from 14 to 5700 μg and from 0.04 to 4600 μg, respectively. Dermal exposure contributed substantially more than inhalation to the total exposure (93.9–100%). Hand contamination ranged from 0.04 to 4600 μg and was the major contributor to dermal exposure. Penetration through specific protective garments was less than 2.4% in all cases, although penetration through general work clothing was as high as 26.8%. The risk evaluation, based on comparison between acceptable daily intake and total absorbed doses, demonstrates that it is presumable to expect possible health effects for workers regularly operating without PPE and improper tractors. Comparisons between exposure levels and operative modalities highlighted that complete PPE and properly equipped tractors contributed to a significant reduction in total exposure to pesticides during agricultural activities. In conclusion, monitored agricultural subcontractors presented very different levels of pesticide exposure due to the high variability of operative modalities and use of PPE. These results indicate the need to critically evaluate the efficacy of training programs required for obtaining a pesticide license in Italy.     

Reproductive disorders associated with pesticide exposure

Exposure of men or women to certain pesticides at sufficient doses may increase the risk for sperm abnormalities, decreased fertility, a deficit of male children, spontaneous abortion, birth defects or fetal growth retardation. Pesticides from workplace or environmental exposures enter breast milk. Certain pesticides have been linked to developmental neurobehavioral problems, altered function of immune cells and possibly childhood leukemia. In well-designed epidemiologic studies, adverse reproductive or developmental effects have been associated with mixed pesticide exposure in occupational settings, particularly when personal protective equipment is not used. Every class of pesticides has at least one agent capable of affecting a reproductive or developmental endpoint in laboratory animals or people, including organophosphates, carbamates, pyrethroids, herbicides, fungicides, fumigants and especially organochlorines. Many of the most toxic pesticides have been banned or restricted in developed nations, but high exposures to these agents are still occurring in the most impoverished countries around the globe. Protective clothing, masks and gloves are more difficult to tolerate in hot, humid weather, or may be unavailable or unaffordable. Counseling patients who are concerned about reproductive and developmental effects of pesticides often involves helping them assess their exposure levels, weigh risks and benefits, and adopt practices to reduce or eliminate their absorbed dose. Patients may not realize that by the first prenatal care visit, most disruptions of organogenesis have already occurred. Planning ahead provides the best chance of lowering risk from pesticides and remediating other risk factors before conception.     

Determining the probability of pesticide exposures among migrant farmworkers: results from a feasibility study.

BACKGROUND: Migrant and seasonal farmworkers are exposed to pesticides through their work with crops and livestock. Because workers are usually unaware of the pesticides applied, specific pesticide exposures cannot be determined by interviews. We conducted a study to determine the feasibility of identifying probable pesticide exposures based on work histories. METHODS: The study included 162 farm workers in seven states. Interviewers obtained a lifetime work history including the crops, tasks, months, and locations worked. We investigated the availability of survey data on pesticide use for crops and livestock in the seven pilot states. Probabilities of use for pesticide types (herbicides, insecticides, fungicides, etc.) and specific chemicals were calculated from the available data for two farm workers. The work histories were chosen to illustrate how the quality of the pesticide use information varied across crops, states, and years. RESULTS: For most vegetable and fruit crops there were regional pesticide use data in the late 1970s, no data in the 1980s, and state-specific data every other year in the 1990s. Annual use surveys for cotton and potatoes began in the late 1980s. For a few crops, including asparagus, broccoli, lettuce, strawberries, plums, and Christmas trees, there were no federal data or data from the seven states before the 1990s. CONCLUSIONS: We conclude that identifying probable pesticide exposures is feasible in some locations. However, the lack of pesticide use data before the 1990s for many crops will limit the quality of historic exposure assessment for most workers.     

Cancer risk assessment for health care workers occupationally exposed to cyclophosphamide

In the present study a cancer risk assessment of occupational exposure to cyclophosphamide (CP), a genotoxic carcinogenic antineoplastic agent, was carried out following two approaches based on (1) data from an animal study and (2) data on primary and secondary tumors in CP-treated patients. Data on the urinary excretion of CP in health care workers were used to estimate the uptake of CP, which ranged from 3.6 to 18 g/day. Based on data from an animal study, cancer risks were calculated for a health care worker with a body weight of 70 kg and a working period of 40 years, 200 days a year (linear extrapolation). The lifetime risks (70 years) of urinary bladder cancer in men and leukemias in men and women were found to be nearly the same and ranged from 95 to 600 per million. Based on the patient studies, cancer risks were calculated by multiplication of the 10-year cumulative incidence per gram of CP in patients by the estimated mean total uptake in health care workers over 10 years, 200 days a year. The risk of leukemias in women over 10 years ranged from 17 to 100 per million using the secondary tumor data (linear extrapolation). Comparable results were obtained for the risk of urinary bladder tumors and leukemias in men and women when primary tumor data were used. Thus, on an annual basis, cancer risks obtained from both the animal and the patient study were nearly the same and ranged from about 1.4 to 10 per million. In The Netherlands it is proposed that, for workers, a cancer risk per compound of one extra cancer case per million a year should be striven for (target risk) and that no risk higher than 100 per million a year (prohibitory risk) should be tolerated. From the animal and the patient study it appears that the target risk is exceeded but that the risk is still below the prohibitory risk.     

Pesticide exposures in professional turf applicators, job titles, and tasks performed: implications of exposure measurement error for epidemiologic study design and interpretation of results

BACKGROUND: Little information on the validity of job title and task classifications, for the prediction of pesticide use or exposure, is available. METHODS: Job titles and task classifications were evaluated in relation to the absorbed dose of herbicides in 98 professional turf applicators. Self-reported use over a 1-week period and other proxies of pesticide use were compared with employer records. RESULTS: Job titles and tasks performed explained (R(2)) 11% and 16% of the variation in dose, respectively. Individuals who sprayed pesticides only, had the highest average doses in the study followed by those spraying and mixing, and those mixing only. The use of 2,4-D products by individual workers over a work season was not related to standardized measures of the amount purchased or used at the company. CONCLUSIONS: These findings suggest that job titles and tasks performed are poor proxies of pesticide use and exposures in professional turf applicators.     

A preliminary report of a surveillance scheme of occupational asthma in the West Midlands

The results from the first year of a notification scheme for occupational asthma in the West Midlands Region are presented. The scheme includes recognised new and old cases of occupational asthma. Thirty new cases were recognised per million general working population in the first year. Cases recognised in different occupational groups ranged from 154 per million painters and assembly workers to three per million clerical staff. Analysis of the agents to which workers with recognised occupational asthma were exposed identified commonly recognised agents such as isocyanates, colophony, and flour and generally less well recognised ones such as oil mists. The distribution of new and old reported cases, including those receiving compensation from the Department of Social Security, were calculated by health authority using estimated working population as the denominator. The number of reported cases varied from 303 per million in a semi-urban health authority that has a respiratory physician with a special interest in occupational asthma to less than 30 cases per million in eight health authorities. The most likely cause for these differences is lack of ascertainment.