Contamination and Distribution of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans (PCDD/F) in Agriculture Fields in Ya-Er Lake Area, China

The contamination and distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from two agricultural fields of a heavily polluted lake area in China (Ya-Er Lake) are presented. The vertical distribution pattern of total PCDD/Fs in soil cores reveals that the maximum concentration was in the layer of 20–30 cm. The concentrations in the top layer of soil at the two sites were similar (17.48 ng/kg at Site 1 and 18.10 ng/kg at Site 2), but the maximum concentration of Site 1 (120.8 ng/kg) was two times higher than that of Site 2 (64.39 ng/kg). The maximum concentration of PCDD/Fs in mud cores in rice fields (0–50 cm) at Sites 1 and 2 was in the layer of 0–10 cm. The maximum PCDD/F concentration in the top layer in mud at Site 1 (203.1 ng/kg) was higher than that at Site 2 (143.3 ng/kg). Significant correlations were found between the mud PCDD/Fs and the organic carbon content (R=0.9743, P<0.05 at Site 1; R=0.9821, P<0.05 at Site 2), the two variables being highly correlated (R=0.9049, P<0.05, at Site 1; R=0.9916, P<0.05 at Site 2). All correlation coefficients were significant at the 95% level. Concentrations were highly correlated with organic carbon, indicating that sorption to organic carbon was the dominant mechanism. Using principal component analysis, the homologue profiles of soil, mud, and plants (rice and radish) were compared. The PCDD/F patterns in plants were found not to be correlated to those in soil and mud. This suggests that atmospheric deposition may be the main source of PCDD/Fs in rice grain. However, mixed exposure involving uptake mechanisms and atmospheric deposition is considered main the source of PCDD/F pollution in radishes.