Differences Between Laboratory And Field Tests For Phytotoxicity Of Copper And Nickel In Soils

Toxicity thresholds of heavy metals in soil play an important role in their ecological riskassessment and highly depend on soil properties. In field condition, after a frequently leaching, the soilconditions might be changed, then the bioavailability of Cu and Ni and their toxicity thresholds in soilvary. However, the differences between laboratory and fiend tests for phytotoxicity of Cu and Ni in soilsare not known in details. This article try to find out the differences between of laboratory and field testsfor different soils with several crops, and study the key factors on the differences.The main results are asfollows:(1) In an alkaline soil of Dezhou, the EC50(the effective concentration of added Cu and Nicausing50%inhibition for plant growth) of Cu for wheat straw and grain are1160mg kg^-1and997mg kg^-1respectively. And in a paddy soil of Jiaxing and an acidic soil of Qiyang, the EC50of Cu andNi for wheat straw and grain are241mg kg^-1,380mg kg^-1and77mg kg^-1and57mg kg^-1ï¼›the EC50of Ni are63mg kg^-1and81mg kg^-1,46mg kg^-1and42mg kg^-1, respectively. The phytotoxicity of Cuand Ni in these soils was in the order:acidic soil> paddy soil> alkaline soil. Soil pH has notable effectson both Cu and Ni toxicity thresholds. It was found higher concentration of Ni than Cu in aerial parts ofcrops, and also Ni is much easier to transfer from straw to grain.(2)The results indicated that the toxicity of Cu and Ni fluctuated yearly. For example, in acidicsoil of Qiyang, the EC50of Cu for maize during2007to2009were111mg kg^-1,96mg kg^-1and132mg kg^-1, respectively; and the EC50of Ni for maize were53mg kg^-1,45mg kg^-1å'Œ30mg kg^-1,respectively. The toxicity of Cu decreased in course of2007to2008, and increased during2008to2009,while the toxicity of Ni increased with time.(3) Soil drying and wetting cyclings had no apparent influence on soil pH and electricalconductivity, however they increased the concentration of dissolved organic carbon markedly. InDezhou alkaline soils, The concentration of water-soluble Cu and Ni was relatively low in alkaline soils,and most exist as the EDTA extractable fraction; In Jiaxing, EDTA extractable Cu concentration stillhigher than water-soluble and exchangeable fraction, but exchangeable Ni had a higher concentrationthan EDTA extractable fraction; In acidic Qiyang soil, concentration of water-soluble and exchangeableCu and Ni, which considered as high bioavailability, higer than that in Dezhou and Jiaxing soils. Soildrying and wetting cyclings had no apparent influence on the transformation of different Cu and Nifractions.(4) Phytotoxicity of Cu and Ni added to soils to local main crops in field sites with contrasting soilphysicochemical properties had obvious difference from laboratory tests. Toxicity of Cu and Ni inDezhou and Qiyang field soils to wheat was underestimated by laboratory wheat tests. The laboratorybioassay of maize, rape and rice could be used to estimate the toxicity of Cu in field maize, rape andrice with caution of underestimating the risk of Ni toxicity to maize and rape in field.