The assessment of biomarkers in sentinel cattle for monitoring vanadium exposure

Abstract

Various potential biomarkers were sampled for vanadium every 3-4 months from Bos indicus beef cattle farmed extensively immediately adjacent (high exposure (HE) group) and two km away (low exposure (LE) group) from a vanadium processing plant, respectively. Vanadium intake (mg vanadium kg(-1) bwt d(-1)) was modelled using environmental and physiological data as inputs. The vanadium intake ranged from 0.57 to 5.44 mg vanadium kg(-1) bwt d(-1) in the HE group and 0.41 to 2.61 mg vanadium kg(-1) bwt d(-1) in the LE group over a five-year period of monitoring. Samples collected from live sentinel animals over the five-year period included caudal coccygeal vertebrae, tail-switch hair, milk, urine, faeces, rib-bone biopsies and a wide range of blood clinical pathology and haematological parameters. The data was analysed for differences in response between the HE and LE groups. Where differences were found, a linear mixed-effects regression model was fitted to model the relationship between the exposure dose and the response variable. The model included the effects of age, duration of exposure and response, and allowed the prediction of the exposure dose given these inputs. Moreover, forty-two adult cattle were slaughtered over the five years. A wide range of tissue samples, rumen content and whole blood were taken from the cattle at slaughter for vanadium determination. In live animals, a difference in response was found between the HE group and LE group with respect to serum albumin (n = 36), monocyte (n = 36) and thrombocyte (n = 36) counts, and hair (n = 2) and faeces (n = 34) vanadium concentrations. No difference in vanadium concentrations could be shown for urine (n = 36), the traditional occupational health biomarker. Regression models are described for serum albumin, monocyte counts, faeces and hair, which showed the most promise as biomarkers. Average concentrations of vanadium in the tissues of slaughtered cattle ranged from 0.08 to 2.94 mg kg(-1) (wet-weight basis) and rumen content contained 16.67 mg kg(-1). Significant correlations were found between the exposure dose (end-dose) just prior to slaughter and the concentrations of vanadium in the coccygeal vertebrae, liver, diaphragm and rib-bone in descending order of magnitude. Other tissues showed poor correlation to the end-dose. Tissue levels of vanadium in healthy cattle include a much wider range than is currently reflected in the literature. The best tissue from slaughter animals for assessing chronic vanadium exposure is probably the liver.