The changes in dioxin and PCB concentrations in different feed materials over time - preliminary study.

For ndl-PCBs, neither the M-K test nor the determination coefficients showed a trend.

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For this category of feed with respect to PCDD/PCDFs, the results of the M-K test for the median and the regression analyses for the median and mean showed a decreasing trend ( Fig. 1 ).

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In the case of dl-PCBs, the approximation curves for the median and mean indicated a negative trend, but the quality of fit of the curves in both cases was unsatisfactory (R2 < 0.19), while the M-K test indicated that there was a decreasing trend only for the median.

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