Vanadium air pollution : a cause of malabsorption and immunosuppression in cattle

Abstract

An epidemiological investigation into an "illthrift" problem occurring on a dairy farm adjacent to an alloy-processing unit, established that the probable cause of the problem was chronic vanadium poisoning. The disease manifested initially in animals 4-18 months old which showed emaciation, chronic diarrhoea and, in some cases, rhinitis, conjunctivitis and recumbency followed by death. Post-mortem (n=17) and clinical-pathology findings (n=60) indicated that malabsorption and immunosuppression 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 apparent 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 fractions of vanadium. Thirty-four of each of these samples were collected at different time intervals (autumn 1990, summer 1991 and winter 1991) and at varying distances and directions from the processing unit, in order 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 area of approximately 1 140 000 m² directly adjacent to the processing unit so that concentration isolines for vanadium could be drawn and the source more conclusively identified. The levels of vanadium were found to be highest closest to the mine, and surface-soil levels were consistently higher than subsoil levels, suggesting aerial pollution, which was confirmed by air sampling. In addition, washed grass samples were 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 high vanadium levels (≤ 1122 ppm) in the surface soils and grass (≤ 558 ppm) on the farm and showed that the major source of vanadium was the adjacent alloy-processing unit.