Impacts of petroleum exploitation activities on the speciation of inorganic arsenic in groundwater

Arsenite (As(III)) is far more toxic than arsenate (As(V)) to human health. To investigate the potential effects of petroleum exploitation activities on the relative abundance of inorganic As(III) and As(V) in groundwater (GW) and GW toxicity, a total of 153 groundwater samples were collected from a number of sampling wells located near and away from an oil-gathering areas through random sampling method. The results show that average As(III)/As(V) value in GW collected from wells away from oil-gathering areas is 0.603 +/- 0.049 while the value from oil-gathering areas is 0.830 +/- 0.050. The As(III)/As(V) ratios in GW samples are negatively correlated with the distance of sampling well to the oil well while positively correlated with the depth of sampling well. Meanwhile, the influence of inorganic As speciation in drip-irrigation solution on the uptake and accumulation of As by Chinese cabbage was studied. When exposed to the same As content in soils for 2 months, arsenic concentrations in shoots and roots increase significantly with an increase in As(III)/As(V) ratio in the drip irrigation water. Petroleum exploitation activities demonstrated the elevated total As level and the As(III) species in nearby GW systems, raising both ecological and human health risks imposed by As.