Occupational-exposure history

Inhalation of crystalline or fused vitreous silica dust, usually overlong periods, causes a disabling, progressive pulmonary disease known as silicosis (84). Amorphous siUcas have not been linked to siUcosis (85), but can cause respiratory irritation. The history and poHtics of siUcosis have been reviewed (86). Standards have been set or recommended for occupational exposures (87,88) and review articles on the health effects of siUca are available (83,89). 

In a case-control study of pesticide factory workers in Brazil exposed to methyl parathion and formulating solvents, the incidence of chromosomal aberrations in lymphocytes was investigated (De Cassia Stocco et al. 1982). Though dichlorodiphenyltrichloroethane (DDT) was coformulated with methyl parathion, blood DDT levels in the methyl parathion-examined workers and "nonexposed" workers were not significantly different. These workers were presumably exposed to methyl parathion via both inhalation and dermal routes however, a dose level was not reported. The exposed workers showed blood cholinesterase depressions between 50 and 75%. However, the baseline blood cholinesterase levels in nonexposed workers were not reported. No increases in the percentage of lymphocytes with chromosome breaks were found in 15 of these workers who were exposed to methyl parathion from 1 week to up to 7 years as compared with controls. The controls consisted of 13 men who had not been occupationally exposed to any chemical and were of comparable age and socioeconomic level. This study is limited because of concomitant exposure to formulating solvents, the recent history of exposure for the workers was not reported, the selection of the control group was not described adequately, and the sample size was limited. 

The a-tocopherol, P-carotene (ATBC) Cancer Prevention study was a randomised-controlled trial that tested the effects of daily doses of either 50 mg (50 lU) vitamin E (all-racemic a-tocopherol acetate), or 20 mg of P-carotene, or both with that of a placebo, in a population of more than 29,000 male smokers for 5-8 years. No reduction in lung cancer or major coronary events was observed with any of the treatments. What was more startling was the unexpected increases in risk of death from lung cancer and ischemic heart disease with P-carotene supplementation (ATBC Cancer Prevention Study Group, 1994). Increases in the risk of both lung cancer and cardiovascular disease mortality were also observed in the P-carotene and Retinol Efficacy Trial (CARET), which tested the effects of combined treatment with 30 mg/d P-carotene and retinyl pahnitate (25,000 lU/d) in 18,000 men and women with a history of cigarette smoking or occupational exposure to asbestos (Hennekens et al, 1996). 

In humans, total PCB concentrations in maternal milk were elevated (>1.1 mg/kg milk fat) in 4 of 122 cases in the New Bedford Harbor vicinity, Massachusetts (Korrick and Altshul 1998). At least one female was occupationally exposed, as judged by the congener profile and history. PCB exposures from fish consumption were likely, but not from residence adjacent to a PCB-contami-nated site. In all four cases, their newborns were full-term and healthy (Korrick and Altshul 1998). 

The diagnosis of COPD is based in part on the patient s symptoms and a history of exposure to risk factors such as tobacco smoke and occupational exposures. 

One case study was identified where a man who had been occupationally exposed to hexachloroethane was treated for a liver tumor (Selden et al. 1989). Exposure had occurred over a period of 6 years as a result of the presence of hexachloroethane in a degassing agent used during aluminum smelting. However, the hexachloroethane reacted at the 700 C use-temperature, releasing a gas that was 96% hexachlorobenzene with small amounts of other chlorinated compounds. Because there was occupational exposure to a mixture of chlorinated compounds rather than just hexachloroethane, it is highly unlikely that the tumor was the result of hexachloroethane exposure alone. Occupational exposure to mineral oil mists for 20 years was also part of the subject s employment history. 

Barnhart, J. M. (1976). History of the uses/applications of fibrous glass, pp. 27-31. In Occupational Exposures to Fibrous Glass A Symposium. NIOSH, U.S. Government Printing Office, Washington, DC. 

Evaluation of workers occupationally exposed to sulfuryl fluoride found no effects attributable to exposure in a series of psychological and neurological tests compared with individuals with no history of exposure. ... 

Two studies were located that reported the occurrence of liver cancer in humans exposed to carbon tetrachloride fumes, both acutely (Tracey and Sherlock 1968) and for longer periods (Johnstone 1948). In the former case, a male died of hepatocellular carcinoma 7 years after acute intoxication with carbon tetrachloride at an age of 59, although he had a history of moderate alcohol consumption (without demonstrable liver cirrhosis). In the second case, a 30- year-old female died of "liver cancer" after 2-3 years of occupational exposure to carbon tetrachloride that was sufficient to produce signs of intoxication. However, this evidence is much too sparse to establish a cause-and-effect relationship. 

Polybrominated Biphenyls. As discussed in Section 3.2.1.2, results from a medical history survey study of workers in a PBB manufacturing plant and a nonexposed group of Wisconsin farm residents indicated an association between occupational exposure to PBBs and the occurrence of acne (Chanda et al. 1982). 

A retrospective assessment of the potential antifertility influence of ethylene dibromide was conducted by studying the reproductive perfonnance of men exposed to ethylene dibromide in the workplace. Data were obtained from four chemical plants manufacturing ethylene dibromide located in the southern part of the United States (Arkansas and Texas). Exposures in the plants ranged from less than 0.5 ppm to 5 ppm [3.8-38 mg/m- ]. Evaluations were made exclusively on the basis of the men s reproductive histories of live births to their wives, subsequent to their occupational exposure. The mmiber of live births was compared with the expected mmiber derived from national fertility tables. One of the four plants studied showed a significant decrease in fertility however, when data from the four plants were combined, there was no significant effect of ethylene dibroniide exposure on reproductive performance (Wong et al., 1979). 

The ability to define a reference population can be a substantial limitation. There may be insufficient information regarding the exposure history of the reference population to a particular contaminant of interest. It is important to know the range of values of a given biomarker in a normal population (NRC 1991), where normal is regarded as without occupational exposure or without observed or hypothetical environmental exposure. However, Schulte and Talaska (1995) point out that pristine populations are rare, so nonexposed populations generally have some exposure of widely varied extent. 

A case control study by Salib and Hillier (1996) examined the possible relationship between the risk of Alzheimer s disease and occupational exposure to airborne aluminum. The occupation histories of patients with a clinical diagnosis of Alzheimer s disease (198 cases) were compared with two control groups patients with dementia other than Alzheimer s disease (164 cases) and patients with diagnoses other than dementia. Occupational histories were obtained from the patients via a questionnaire. No significant association between occupational exposure to aluminum dust or fumes and the risk of Alzheimer s disease were found (the odds ratio for the comparison with all controls was 0.98, 95% confidence interval of 0.53-1.75). 

Occupational Exposure. Exposures to 2,3,7,8-TCDD, one of the most potent of the CDD congeners, have occurred occupationally in workers involved in the manufacture and application of trichlorophenols and the chlorophenoxy acid herbicides 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T). Holmstedt (1980) has reviewed the history of industrial exposures that have occurred between 1949 and 1976, and Kogevinas et al. (1997) summarized recent data on these cohorts. 

In the communities surrounding the Rocky Mountain Arsenal, a Superfund site in Colorado, USA, pathways for exposure to arsenic were evaluated through analysis of residence history, occupation, hobbies, dietary habits, water supply, housing, and activity patterns (Reif et al., 1993). Children of Hispanic origin or non-Caucasian children who drank less than three glasses of water daily and children who spent more time outdoors had an increased risk of having more than 10 pg/1 of arsenic in their urine (Reif et al., 1993). 

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