森林土壤对几种重金属污染的“记忆”效应

"Memory" effects of heavy metals on forest soils

采用一定浓度(40～120mg·L-1)Cd、Cr、Pb的氯化物溶液多次浇灌森林土壤,研究受以前污灌影响而导致某次污灌后土壤对重金属的吸持率下降的效应———"记忆"效应。结果表明:土壤对Cr和Pb环境容量大,"记忆"效应不明显。多次浇灌CrCl3溶液后,土壤剖面20cm以下采样点约99%的Cr被土壤吸持;3次浇灌PbCl2后各采样点Pb浓度下降率维持在85%以上,但污灌次数进一步增加,则土壤的吸持率下降。Cd的环境容量较小,增加投入会很快使土壤上层对其吸附达到饱和,吸附带随之下移,对地下水的安全构成威胁。

By irrigating a forest soil with a solution containing a certain concentration of Cd,Cr and Pb several times,'memory'effect on the soil,i.e.decrease in the heavy metal adsorption rate of the soil as was affected by sewaging in the past,was studied.Results show that the soil has a high environmental capacity for Cr and Pb,so the 'memory' effect of the soil is not significant.After irrigation with CrCl 3 solution several times,about 99% of the Cr in the soil below 20 cm was adsorbed by the soil.After irrigation with PbCl 2 three times,Pb concentrations at various sampling points declined but remained over 85%.If more irrigation was done,the Pb adsorption rate would further go down.The soil is rather limited in environmental capacity for Cd.The surface soil layer would easily get saturated in adsorption and the adsorption zone would move downwards,posing a threat to the groundwater.