The Sixteenth Conference of the International Society for Environmental Epidemiology (ISEE): Abstracts
To assess potential for carcinogenic risks and target organs from occupational exposure to alpha-particles in unmilled visible (>10 u in diameter) phosphate dusts.
Air pollution epidemiology focuses on the health effects of particles <10 u in diameter. Consensus holds that lung cancer is the major health risk from exposure to the particulate daughters of radon gas. Radon, however, is a noble gas and therefore is fat soluble. Previously, we had reported two adult teachers, one male with multiple myeloma, and one female with breast cancer following massive exposures to radon gas in a school. In 1993, we evaluated a 35 y male with nasopharyngyoma and occupational exposures to phosphates in a port hanger storage depot.
Observational cohort, using mean ages of cases to obtain expected rates from National Cancer Registry (All males, Jews). The work population consisted of 34 workers first employed in the 1970’s and accumulating 1068 years of follow-up. The workers were exposed to untreated phosphates from natural sources undergoing no milling or grinding. Observations indicated massive air contamination with visible dust particles. Episodic past monitoring indicated high levels of alpha radiation in air sampling. Although we do not have measures of particle size distribution, we hypothesize that the majority of the particles were greater than 10 u in diameter.
There were 7 cancers (age of onset X=50; range: 35–64; latency 13–36 y) including the index case, 1 nasopharyngeal (age 35, latency 13 y); 3 stomach (age range: 46–51; latency 15–25 y); 2 renal (age range: 56–59; latency 19–26 y), and 1 lymphoma (age: 64; latency 36 y). O/E ratios for all cancers were 0.76 (p<.05), nasopharyngeal, 16.8 (p<.01); stomach cancer 10.1 (p<.01); renal 2.1 (p<.01) and lymphoma 0.65 (p<.01). There were no cases of lung cancer.
The increased risks and target sites for the extrapulmonary tumors are consistent with the classic industrial hygiene principle that particles with diameter greater than 10 u, when taken into the nasal and pharyngeal passages, are sent back upward and swallowed, and their major target organs are the (1) nasopharyngeal area and (2) the gastrointestinal tract. There is a coherent fit between the physiology and distribution of phosphates and the pattern of distribution of the types of cancer. We suggest the hypothesis that high exposures to phosphate dust >10 u increases risks for extrapulmonary tumors via concentrated transfer of ionizing radiation to the local tissue.