An Evaluation of the Risks Associated with the Ingestion of Lead Contaminated Soil, Water and Plants by Grazing Cattle. J. W. Knight, B. D. Beck and A. P. Toole, Gradient Corporation, 3775 Iris Avenue, Suite 6, Boulder, CO 80301; and Gradient Corporation, 44 Brattle Street, Cambridge, MA 02138
This paper presents a method, applicable to sites in southwest U.S., to quantify the risks associated with the ingestion of lead in soil, water and plants (specifically prickly pears) by grazing cattle. The scientific literature was reviewed to estimate a chronic no observeable adverse effect level (NOAEL) of 3 to 5 mg kg-1day-1. Screening calculations indicated that a dose of 3 mg kg-1day-1 to adult cattle would also be protective for their nursing calves. A series of equations were then developed to estimate grazing cattle lead exposure via soil, water and plant lead concentrations. These equations included estimates of daily cattle intake of soil, water and plants (dry weight basis). The exposure equations were applied to a hypothetical site and the resulting total estimated lead intake compared to the NOAEL of 3 mg kg-1day-1.
The human health risks associated with the ingestion of beef products originating from a hypothetical site with elevated lead levels were also quantified in this assessment. As a health protective endpoint for humans, a lead in beef exposure level for children of 18 mg day-1 was selected. When added to background exposures, 18 mg lead per day, is expected to result in blood lead concentrations greater than 10 mg dL-1 in less than 5% of the exposed children. Results of the human health risk assessment indicated that soil lead levels to protect grazing cattle will usually be more restrictive than those necessary to protect humans consuming beef from those cattle. This methodology can be adapted for use at other sites to assess risks of lead deposited on agricultural lands.