Movement of water and heavy metals (Zn, Cu, Pb and Ni) through sand and sandy loam amended with biosolids under steady-state hydrological conditions

New guidelines for using biosolids in UK agriculture favour the use of enha nced treated biosolids, such as dried and composted cakes, due to concerns about the potential for transfer of pathogens into the food chain. However, there is a need to ensure that their use is environmentally acceptable and does not increase the risk to potable water supplies or the food chain fro m other contaminants such as heavy metals and xenobiotic organic chemicals. The objective of this study was to determine whether the use of composted and dried mesophilic anaerobically digested dewatered (MADD) biosolids woul d increase the risk of heavy metal leaching from cultivated horizons when c ompared to more conventionally used MADD cake. Three biosolids (MADD sewage sludge cake - fresh, dried and composted) were mixed with a sand (typic qu artzipsamments. %OM = 3.0. pH = 6.5) or a sandy loam (typic hapludalf, %OM = 4.8, pH = 7.6) at an application rate equivalent to 250 kg N/ha/y resulti ng in loadings of approximately Zn: 6 mug, Cu: 2 mug, Ph. 5 mug and Ni: 0.2 mug/g of soil dry weight basis. These amended soils were repacked into col umns (0.4 m by 0.1 m internal diameter) and leaching of Zn, Cu, Pb and Ni w as investigated following application of two 24 h simulated rainfall events of 4.5 mm/h. Water balance data and the use of conservative tracers (Cl- a nd Br-) showed that the hydrological regimes of each core were comparable a nd, thus, unlikely to account for differences in metal leaching observed. A lthough no significant difference (P = 0.05) was observed between biosolid amended and control soils, those amended with composted sludge consistently gave higher loss of all metals than did the control soils. Total losses of metals from compost amended soil over the two rainfall events were in the ranges, Zn:20.5-58.2, Cu:9.0-30.5, Pb:24.251.2 and Ni:16.0-39.8 mug metal/k g amended soil, compared with Zn:16.4-41.1, Cu:6.2-25.3, Pb:16.9-41.7, and Ni:3.7-25.4 mug metal/kg soil from the control soils. Losses of Zn, Cu, Ph and Ni from fresh MADD cake amended soils (19.8-41.3, 3.2-25.8, 21.6-51.6 a nd 7.6-36.5 mug metal/kg amended soil, respectively) and from dry MADD cake amended soils (10.7-36.7, 1.8-23.8, 21.2-51.2 and 6.8-39.2 mug metal/kg am ended soil, respectively) were similar to the controls. Generally, quantiti es of metals leached followed the order Zn = ph > Cu > Ni, which was consis tent with the levels of metals in the original sludge/soil mixtures. These results suggest that composting or drying MADD biosolids is unlikely to inc rease the risk of groundwater contamination when compared to the use of MAD D cake; therefore, the changes in UK sludge use in agriculture guidelines a re satisfactory in this respect. (C) 2001 Elsevier Science Ltd. All rights reserved.