VANADIUM AIR-POLLUTION - A CAUSE OF MALABSORPTION AND IMMUNOSUPPRESSION IN CATTLE

An epidemiological investigation into an ''illthrift'' problem occurri ng on a dairy farm adjacent to an alloy-processing unit, established t hat the probable cause of the problem was chronic vanadium poisoning. The disease manifested initially in animals 4-18 months old which show ed emaciation, chronic diarrhoea and, in some cases, rhinitis, conjunc tivitis and recumbency followed by death. Post-mortem (n = 17) and cli nical-pathology findings (n = 60) indicated that malabsorption and imm unosuppression were the basis of the pathogenesis in affected animals. Eight months after the commencement of the investigation, adult cows began showing evidence of emaciation, reduced milk production and an a pparent increase in the number of abortions, stillbirths and dystocias . Over a 2-year period, 134 surface-soil samples, 134 subsoil samples and 134 grass samples from the farm were analysed for various fraction s of vanadium. Thirty-four of each of these samples were collected at different time intervals (autumn 1990, summer 1991 and winter 1991) an d at varying distances and directions from the processing unit, in ord er to gauge the magnitude of the problem, and the distribution pattern of vanadium, and to identify possible seasonal trends. The remaining 100 of each of these samples were taken at 100-m intervals over an are a of approximately 1140 000 m(2) directly adjacent to the processing u nit so that concentration isolines for vanadium could be drawn and the source more conclusively identified. The levels of vanadium were foun d to be highest closest to the mine, and surface-soil levels were cons istently higher than subsoil levels, suggesting aerial pollution, whic h was confirmed by air sampling. In addition, washed grass samples wer e considerably lower in vanadium than the unwashed samples, indicating that most of the vanadium was in the dust on the plants. The highest levels of vanadium were found in the soil during the summer and on the grass during the winter. These analyses confirmed the presence of hig h vanadium levels (less than or equal to 1122 ppm) in the surface soil s and grass (less than or equal to 558 ppm) on the farm and showed tha t the major source of vanadium was the adjacent alloy-processing unit.