Polychlorinated biphenyls (PCBs) are typical representative of chlorinated organic pollutants. Given the toxicity of PCBs, there is an urgent need to select an appropriate indicator to monitor their biological effects on soil ecosystems. For this purpose, we investigated the impacts of PCBs on soil protein and the potential of using protein as a biological indicator to assess soil contamination due to PCBs. This study demonstrated that soil protein concentration and expression were negatively affected by PCBs. In addition, significantly ( ) negative correlation was observed between protein concentration and PCBs. Subsequently, protein size distribution separated by SDS-PAGE revealed that with the increase in PCBs concentration there are less large molecular weight proteins and more low molecular weight proteins ( 40？kD). Consequently, soil protein level has the potential to be an indicator of soil contamination, and these low molecular weight proteins have significant meaning for getting insight into the ecological effects of PCBs on the soil environment. 1. Introduction Chlorinated organic chemicals probably constitute half of the environmental organic pollutants problems worldwide. Polychlorinated biphenyls (PCBs) almost all come from anthropogenic origin (mostly from electronic and electrical waste, called e-waste, and recycling activity) and are one of the two chlorinated chemical classes that cause the most extensive environmental pollution [1, 2]. Since they are highly resistant to degradation, with very low solubility in water and being combined with soil organic matter, they remain in the soil for many years. Furthermore, because they are lipophilic in nature, they are passed through the food chain and are bioaccumulated in organisms. Consequently, PCBs have great negative effects on plants and microorganisms; they harm the whole soil biosphere, finally threatening human health [2–6]. Given the toxicity of PCBs, there is an urgent need to monitor their biological effects on the soil ecosystems. The physical, chemical, and biological indicators are three important properties for monitoring and assessing soil contamination. Biological indicators, especially enzyme activity, for its sensitivity to the changes in pollutants, is closely related to nutrient cycles and easy to determinate, has become the most widely used property to monitor soil function and health [7–9]. Although enzyme activity has these advantages, much literature has indicated that contaminated soil is a complex system, and the interaction of pollutants, especially organic
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