A simplified method for determination of organic mercury in soils

Abstract

Monitoring levels of organic mercury species at very low concentrations in the environment is of concern due to their high toxicity. However, conventional methods for organic mercury determination are usually expensive and time consuming because they involve many preparation steps and require instrumentation which is not available in most laboratories. In order to make it easier the organic mercury determination this paper presents a simple, fast and reliable extraction method for isolating and quantifying the organic mercury fraction in soil samples. The proposed method is based on one single digestion stage using a CuBr₂ solution in HCl to release the organic mercury compounds from the solid matrix and their simultaneous and selective extraction into dichloromethane. After the separation of the organic phase, reextraction into aqueous media using N-acetyl-L-cysteine solution allows the determination of the extracted organic mercury by electrothermal atomic absorption spectrometry with the direct mercury analyzer DMA-80. Experimental and instrumental variables were optimized by the analysis of synthetic samples of methylmercury dispersed in pulverized silica. The method was validated by the analysis of the certified CRM 580 reference material. The detection limit of the procedure is 9.6 ng of organic mercury per gram of dry soil. The applicability of the proposed method to real samples was demonstrated through recovery studies of methylmercury in spiked soils. In addition, the influence of the TOC (Total Organic Carbon) content in soils was studied. The recoveries obtained under optimal experimental conditions ranged from 90% to 105% for all tested samples, indicating the suitability of the proposed method for determination of the organic mercury fraction in soils.