Levels of dioxins in soil and corn tissues after 30 years of biosolids application.

Detectable levels of dioxins have been reported in biosolids, but very little information is available on the effect of long-term application of biosolids on dioxins accumulation in soil and uptake by plants. We analyzed dioxins in soil and corn tissue samples from field plots after 30 continuous applications of biosolids at 0 (Control), 16.8, and 67.2 Mg biosolids ha -1 yr -1 resulting in 0, 504, and 2016 Mg ha -1 cumulative loadings of biosolids, respectively. The levels of dioxins in soil were only 79.9, 115.5, and 247.5 ng toxic equivalents (TEQs) kg -1 in the 0, 504, and 2016 Mg biosolids ha -1 plots, respectively. Dioxins were not detected in the corn grain, and only trace levels (6.8-7.5 ng TEQs kg -1 ) were found in the corn stover; however, these values were not statistically different between control and biosolids-amended soils. These observations suggest that although long-term application of biosolids may increase the levels of dioxins in soil, it does not affect dioxins uptake by corn.