Recent survey and effects of cooking processes on levels of PCDDs, PCDFs and Co-PCBs in leafy vegetables in Japan

We report here the latest levels of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) and coplanar polychlorinated biphenyls (Co-PCBs) in leafy vegetables in Japan as well as the effect of cooking processes on the reduction of these contaminants. Three kinds of leafy vegetables (“komatsuna”, lettuce and spinach) from seven districts in Japan in 1998 were analyzed for the 2,3,7,8-chlorine substituted PCDD/Fs and three non-ortho-PCBs (#77, 126 and 169). The mean total TEQ levels (using the WHO-TEFs) in the komatsuna, lettuce and spinach were 0.094, 0.025 and 0.196 pg/g fresh weight, respectively. The TEQ levels are dominated by 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, 2,3,4,7,8-PeCDF and 3,3′,4,4′,5-PeCB in many of the samples. For one of these isomers, the 2,3,4,7,8-PeCDF TEQ levels showed good correlation with the total TEQ levels in the samples (r=0.957). This suggests that 2,3,4,7,8-PeCDF may be an indicator for dioxin contamination in the analysis of the leafy vegetables. Also, the effects of two cooking processes (washing and washing followed by boiling) on the dioxin levels in two types of spinach samples were investigated. On average, in both samples, the total concentrations of the PCDDs, PCDFs and Co-PCB were reduced to about 38%, 73% and 88% of the initial concentrations by washing, and to 21%, 35% and 61% of the initial concentrations by washing followed by boiling. The total TEQ levels were reduced to about 30% of the initial TEQ levels by washing followed by boiling. Significant reductions in the TEQ levels were observed in the cooked samples. Thus, the cooking processes may reduce the risk of dioxin intake from the leafy vegetables.