Effects of biosolids and compost amendment on chemistry of soils contaminated with copper from mining activities

Several million metric tons of mining wastes, called stamp sands, were generated in the Upper Peninsula of Michigan during extensive copper (Cu) mining activities in the past. These materials, containing large amounts of Cu, were discharged into various offshoots of Lake Superior. Due to evidences of Cu toxicity on aquatic organisms, in due course, the materials were dredged and dumped on lake shores, thus converting these areas into vast, fallow lands. Erosion of these Cu-contaminated stamp sands back to the lakes is severely affecting aquatic life. A lack of uniform vegetation cover on stamp sands is facilitating this erosion. Understanding the fact that unless the stamp sands are fertilized to the point of sustaining vegetation growth, the problem with erosion and water quality degradation will continue, amending the stamp sands with locally available biosolids and composts, was considered. The purpose of the reported study was to assess potential effects of such organic fertilizer amendments on soil quality. As the first step of a combined laboratory and greenhouse study, a 2-month-long incubation experiment was performed to investigate the effects of biosolids and compost addition on the soil nutrient profile of stamp sands and organic matter content. Results showed that both biosolids and compost amendments resulted in significant increase in nitrogen and phosphorus concentrations and organic matter contents of stamp sands. Sequential extraction data demonstrated that Cu was mostly present as bound forms in stamp sands, and there was no significant increase in the plant available fraction of Cu because of fertilizer application.