Effects of soil metal(loid)s pollution on microbial activities and environmental risks in an abandoned chemical smelting site

Abandoned chemical smelting sites containing toxic substances can seriously threaten and pose a risk to the surrounding ecological environment.Soil samples were collected from different depths(0 to 13 m)and analyzed for metal(loid)s content and fractionation,as well as microbial activities.The potential ecological risk indices for the different soil depths(ordered from high to low)were:1 m(D-1)>surface(S-0)>5 m(D-5)>13 m(D-13)>9 m(D-9),ranging between 1840.65-13,089.62,and representing extremely high environmental risks,of which Cd(and probably not arsenic)contributed to the highest environmental risk.A modified combined pollution risk index(MCR)combining total content and mobile proportion of metal(loid)s,and relative toxicities,was used to evaluate the degree of contamination and potential environmental risks.For the near-surface samples(S-0 and D-1 layers),the MCR considered that As,Cd,Pb,Sb,and Zn achieved high and alarming degrees of contamination,whereas Fe,Mn,and Ti were negligible or low to moderate pollution degrees.Combined microcalorimetry and enzymatic activity measurements of contaminated soil samples were used to assess the microbial metabolic activity characteristics.Correlation analysis elucidated the relationship between metal(loid)s exchangeable fraction or content and microbial activity characteristics(p<0.05).The microbial metabolic activity in the D-1 layer was low presumably due to heavy metal stress.Enzyme activity indicators and microcalorimetric growth rate(k)measurements were considered sensitive indicators to reflect the soil microbial activities in abandoned chemical smelting sites.

Enduring legacy of coal mining on the fungal community in a High Arctic soil after five decades

Mineral extraction is known to affect soil fungi in polar environments,but it is unknown how long these effects persist.Here,by amplifying the internal transcribed spacer regions of rRNA genes in soil fungi,we compared soil fungal community in intact natural tundra with that in a nearby former coal mining area,abandoned 52 years previously,on Svalbard in the High Arctic.Compared with those in intact tundra,soils in the former mining area were more acidic and had lower plant coverage.Despite of similar diversity in the two areas,the fungal community was dominated by Basidiomycota in the intact tundra,but by Ascomycota in the former mining area.Ectomycorrhizal genera formed a major part of the tundra community,but were notably less abundant in the mining area.The principal variation among samples was soil pH.Surprisingly,network connectivity analysis indicated that the fungal community in the former mining area had greater network connectivity than that in the tundra area.Overall,the ecosystem in the former mining area has made only limited recovery towards the natural tundra state even after more than five decades.It is unclear whether the recovery of the fungal community is limited more by the low primary productivity,slow migration of fungi and plants,or slow changes in soil parameters.Our findings emphasize the susceptibility of polar ecosystems to disturbance,given their particularly slow recovery back towards the natural state.