Stereoselective accumulations of hexachlorocyclohexanes (HCHs) are correlated with Sphingomonas spp. in agricultural soils across China

Highlights: • β-HCH was more abundant than other HCH isomers in farmland topsoils across China. • Preferential degradation of (−)-α-HCH was universal but uncorrelated with linA1. • Sphingomonas was a promising biomarker indicating total-HCH, β-HCH, and α-HCH EF. • HCH-degrading microbe and relevant function were greatly influenced by soil moisture. The wide usage of hexachlorocyclohexanes (HCHs) as pesticides has caused soil pollution and adverse health effects through direct contact or bioaccumulation in the food chain. This study quantified major HCH isomers in farmland topsoils across China, and evaluated their correlations with microbial community structure, function, and abiotic variables (e.g., moisture, pH, and temperature). Recalcitrant β-HCH was more abundant than α-, γ-, and δ-HCHs, and α-HCH enantiomeric fractions (EF) were larger than 0.5, indicating preferential degradation of (−)-α-HCH. Sphingomonas was not only a predominant population (especially in samples collected in the south), but also a promising biomarker indicating total- and β-HCH residuals, and EF values of α-HCH. Soil moisture and temperature were among the most influential factors that structured the diversity and function of soil microbial communities. The results suggested that increasing soil moisture (in the range of 5–45%) would benefit the growth of HCH-degrading populations and the enrichment of HCH-degradation related pathways. Revealing the site-specific relationships between topsoil physical, chemical, and microbial properties will benefit the in situ bioremediation of farmlands with relatively low HCH residuals across the world.