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.
