Summary of phytotoxic levels of soil arsenic

In the absence of site-specific data, generic guidelines are important to indicate whether soils contaminated with As require attention or remediation. It is important that the data used to set generic guidelines come from as broad a survey as possible. The objective of this paper is to summarize the data on the phytotoxicity of As from the literature, and to analyze the associated variance. The very narrow margin between background and toxic concentrations of As in soils is clearly shown. The source of As is important; the inorganic sources are less toxic than the organic sources. When only the inorganic sources are considered, soil type is the only other significant variable. Monocotyledonous and dicotyledonous plants did not differ significantly in response to soil As. Inorganic As is 5-fold more toxic in sands and loams (the geometric mean, GM, of the reported toxicity thresholds is 40 mg kg-1) than in clay soils (where the GM is 200 mg kg-1). Deviation of a single geometric standard deviation is 3.6-fold above and below these GM values. The results show that it is appropriate to set generic regulatory criteria by soil type, but that site- or soil-specific data is likely needed past a screening stage.