Solubility of arsenic and its uptake by ryegrass from polluted soils amended with organic matter

Abstract

The study focused on suitability of ryegrass (Lolium perenne) for phytostabilization of As-polluted soils as well as on the effects of soil amendment with organic matter on the solubility of As. Four soil samples, containing 505–6500mg·kg−1 As, were collected from the areas of historical ore mining and processing in Złoty Stok and Radzimowice (Poland). Soils were amended with different organic materials, i.e. cattle manure (M), three kinds of variously treated sewage sludge (fresh SS1, digested and limed SS2, and composted SS3), and two kinds of forest litter (representative of pine and alder stands FL1, FL2). In a three-month incubation experiment, the changes of As concentrations in water extracts and As extractability with 0.01M CaCl2 were measured. After that time, a pot experiment with ryegrass was established. Soil amendment with all organic materials caused an initial increase in As solubility and extractability that decreased during incubation, but in most cases remained higher compared to untreated samples. Plant growth and As concentrations in plant roots and shoots depended both on soil properties and on the kind of amendment. Sewage sludge SS2 and forest litters caused adverse effects on plant growth, except for the least polluted soil 4, while application of M, SS1 and SS3 posed beneficial effects. Unlike As extractability, its uptake by ryegrass was reduced in organic matter-amended soils, particularly those treated with SS2 and SS3, which was reflected by an amendment factor AF. In spite of that fact, the concentrations of As in shoots of ryegrass grown in soils 1 and 2 were assessed as relatively high and often exceeded 50mg·kg−1. The effects of soil treatment with organic amendments on As phytoavailability to ryegrass turned out difficult to predict and therefore should be experimentally determined in each case of remediation.