Use of dogs as indicators of metal exposure in rural and urban habitats in NW Spain

Many different species have been used in environmental biomonitoring studies in diverse habitats including forest, farmland, and urban and sub-urban areas. However, there is little information on domestic animals living in rural or urban habitats and exposed to the same pollutants as the human population. In this connection, pets could prove to be good indicators of human metal exposure since they closely share the same environment as their owners, and are therefore exposed, at least in part, to the same pollutants. The present study investigated toxic metal exposure in dogs in NW Spain and compared metal exposures between dogs from rural and urban habitats, considering the influence of diet, sex and age. Samples of liver and kidney from 57 male and female dogs, aged between 6 months and 18 years, were collected after euthanasia at veterinary clinics. Samples were acid-digested and metal concentrations determined by ICP-MS. Geometric mean concentrations of metals in the liver and kidney (microg/kg wet weight) were 12.6 and 15.9 for arsenic, 58.0 and 175 for cadmium, 32.7 and 53.4 for mercury, and 57.7 and 23.1 respectively. Hepatic lead concentrations were significantly higher (p<0.05) in dogs fed commercial diets than dogs fed home-made feed (32%) or a mixture of commercial and home-made feeds (95%). Mercury concentrations in the kidney were significantly higher (3-fold, p<0.05) in dogs from urban areas than in dogs from rural areas. Cadmium levels in kidney were significantly higher (p<0.05) in females (67%) and increased with age (p<0.001). Although no human samples were obtained in this study and no direct correlations between dogs and human metal exposure have been conducted, given our results pets could be suggested as surrogate indicators of human metal exposure.