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• The pool size and speciation of soil Hg in the study area indicate the risk of downward migration and diffusion of soil Hg. • The soil Hg in forestland showed stronger vertical migration than that in farmland. • Potential groundwater Hg input was dominated by soil Hg. Guizhou Province is located in the heart of a karst zone in southwest China, which is one of the largest karst areas in the world. Given the fragile surface ecosystem and highly developed underground karst structure, the migration and transformation of soil Hg may impact groundwater quality in karst environments with high Hg background concentrations. This study examines the vertical migration and transformation of soil mercury (Hg) in two karst catchments, Huilong and Chenqi, with the former containing high Hg contents associated with mineralization and the latter representing regional background Hg. The results show that the soil Hg pool in the Huilong catchment was as high as 44.4 ± 4.2 g m−2, whereas in the Chenqi catchment was only 0.17±0.02 g m−2. Compared with farmland soil, forest soil showed a significant loss of Hg. The results of L 3 X-ray absorption near edge structure of Hg indicated that α-HgS, the primary mineral of Hg ore, gradually changed to other mineral types during soil formation. In Huilong catchment, the proportion of organic bound Hg(SR) 2 out of total Hg decreased from 44.0% to 20.3% when soil depth increased from 10 cm to 160 cm in farmland soil profile and from 39.3% to 34.5% in forest soil profile, while the proportion of ionic Hg increased with soil depth, from 4.2% to 10.7% in the farmland soil profile and from 6.7% to 11.6% in the forestland soil profile. Results from the triple-mixing isotope model show that soil Hg accounts for more than 80% Hg in groundwater in the two catchments. Results from this study indicate potential risks of soil Hg entering into groundwater in this karst area. [Display omitted] [ABSTRACT FROM AUTHOR]

Seasonal atmospheric particulate matter samples with different particle sizes (< 2.5 μm [PM 2.5 ], 2.5-5 μm [PM 2.5-5 ], 5-10 μm [PM 5-10 ], and 10-100 μm [PM 10-100 ]) were collected to analyze the mass concentration and distribution characteristics of nine water-soluble ions (WSIs; F - , Cl - , NO 3 - , SO 4 2- , Na + , NH 4 + ) in Lvliang in China. The results of chemical composition analysis indicated that the average concentration of total WSIs was 29.08 µg·m + , Mg 2+ , and Ca 2+ ) in Lvliang in China. The results of chemical composition analysis indicated that the average concentration of total WSIs was 29.08 µg·m -3 and accounted for 40.45% of PM 2.5 , 80.99% of which was attributable to SO 4 2- , NH 4 + , and NO 3 - ; the concentration demonstrated obvious distribution characteristics. NO 3 - and NH 4 + primarily exist as NH 4 NO 3 and (NH 4 ) 2 SO 4 , respectively, in fine particles but as NaNO 3 and NH 4 Cl, respectively, in coarse particles. The PM 2.5 was alkaline overall, and K + and NH 4 + caused the highest R C/A values in autumn. Stationary sources contribute more to WSIs in particulates than mobile sources. The secondary transformation degree of SO 2 was higher than that of NOx, especially in fine particles. The positive matrix factorization (PMF) and potential source contribution function (PSCF) models were combined to determine the sources of WSIs in PM 2.5 . Through use of the PMF model, five source factors were categorized: secondary aerosols (43.0%), biomass combustion (21.7%), coal combustion (17.6%), dust (10.9%), and vehicular traffic (6.8%). The results of the PSCF model suggested that the transport of pollutants from Shanxi, northwestern Shaanxi, Gansu, Inner Mongolia and Henan, had the greatest effect on air quality in Lvliang., (© 2023. The Author(s), under exclusive licence to Springer Nature B.V.)