Journal
ENVIRONMENTAL SCIENCE & TECHNOLOGY
Volume -, Issue -, Pages -Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.est.3c03682
Keywords
PCDD/Fs; aqua regia; soil digestion; emission
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This study discovered abundant dioxin formation in soil and organic carbon-containing matrices after digestion, with significant correlation observed between Sigma 17PCDD/F concentration and soil organic carbon content. Humic acid was found to be an important component in the conversion of organic matter to PCDD/Fs during digestion. The strong oxidation and production of reactive chlorine by aqua regia were identified as key factors in PCDD/F formation. The annual emission of PCDD/Fs due to digestion with strong acids by the inspection and testing industry was estimated to be 83.8 g TEQ in China in 2021, highlighting the importance of addressing unexpected dioxin formation during digestion processes.
Dioxins, such as polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs), are among the most toxic unintentionally produced persistent organic pollutants, and their emission is of great concern. Herein, we discovered abundant dioxin formation in soil and various organic carbon-containing matrices after digestion with aqua regia. Sigma 17PCDD/Fs concentrations were in the range of 66.6-142,834 pg/g dw (5.6-17,021 pg WHO2005-TEQ/g dw) in 19 soil samples after digestion with aqua regia for 6 h. Sigma 17PCDD/Fs concentration was significantly and positively correlated with soil organic carbon content (R-2 = 0.89; p < 0.01). Compared with cellulose and lignin, humic acid served as an important organic matter component that was converted to PCDD/Fs during soil digestion. Strong oxidation and production of reactive chlorine by aqua regia may be the key factors in the formation of PCDD/Fs. The yearly emission of PCDD/Fs due to digestion with strong acids by the inspection and testing industry was estimated to be 83.8 g TEQ in China in 2021 based on the highest level, which was similar to 0.9% of the total dioxin inventory in China. Great attention should be paid to unexpected dioxin formation during digestion processes considering the potential risk of release from laboratories and enterprises.
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