ACCUMULATION OF POTENTIALLY TOXIC ELEMENTS BY SHEEP GIVEN DIETS CONTAINING SOIL AND SEWAGE-SLUDGE - 2 - EFFECT OF THE INGESTION OF SOILS TREATED HISTORICALLY WITH SEWAGE-SLUDGE

Current European Union legislation will increase the level of disposal of sewage sludge to agricultural land in the next 10 years. This incr ease may lead to an increase in ingestion, fry grazing animals, of her bage with elevated levels of potentially toxic elements (PTEs) derived from sludge adhered to the herbage or sewage sludge-amended soil resu lting in the accumulation of PTEs in body tissues, especially the live r and kidney. To assess the possible accumulation of PTEs from soils t reated historically with sewage sludge, eight groups of housed weaned lambs were given either dried grass as a sole food (grass central), or diets comprising dried grass (0.9 of total diet dry matter (DM)) and soil (0.1 of total diet DM) from two experimental sites, plots within which had been treated 14 years previously with different quantities o f sewage sludge. Soils from the two sites (Cassington and Royston) had contrasting physical characteristics, pH and contents of calcium. The soil from the site at Cassington was slightly acidic (pH 6.0) and had a concentration of calcium of 7.92 g/kg DM whereas the soil from the site at Royston was alkaline (pH 8.0) and had a high concentration of calcium (23.5 g/kg DM). Plots at each site had a range of concentratio ns of cadmium (Cd) in the soil up to three times the United Kingdom (U K) statutory limit of 3 mg Cd per kg DM. The soils from these two site s were designated control - no amendment with sewage sludge (0.69 mg C d per kg DM) low (3.55 mg Cd per kg DM), medium (6.63 mg Cd per kg DM) and high (8.82 mg Cd per kg DM; Cassington soil only). Voluntary DM i ntake of diets by weaned lambs (mean 1436 g/day) was not affected sign ificantly by any dietary treatment. The concentrations of Cd in liver increased (P < 0.001) from 0.062 and 0.072 mg/kg DM (Royston and Cassi ngton control, respectively) to 0.218 and 0.403 mg/kg DM (Royston and Cassington medium, respectively) and 0.500 mg/kg DM (Cassington high). The concentrations of Pb in liver increased (P < 0.001)from 0.733 and 0.627 mg/kg DM (Royston and Cassington control, respectively) to 1.18 and 1.25 mg/kg DM (Royston and Cassington medium respectively) and 1. 18 mg/kg DM (Cassington high). Similar changes were observed for conce ntrations of Cd and Pb in kidney. A depletion of the concentration of Cu in the liver was observed in all treatments containing soil in the diet. The rate of accumulation of Cd in the liver ranged from 0 to 0.3 5 mu g/g daily tissue DM growth and in the kidney ranged from 0 to 0.4 4 mu g/g daily tissue DM growth. The rate of accumulation of Pb in the liver ranged from 0. to 6.01 mu g/g daily tissue DM growth and in the kidney ranged from 0 to 0.63 mu g/g daily tissue DM growth. No signif icant accumulation of PTEs was observed in muscle tissue. It is conclu ded that the current UK statutory limits for the concentrations of Cd and Pb in sails treated with sewage sludge should be reviewed in the l ight of these results, though they require confirmation in the grazing situation.