[en] Elevated fluoride (F) concentration in groundwater is posing a public health risk in the Manas River Basin (MRB), Northwest China. Based on the characterization of regional groundwater flow, 90 groundwater samples from aquifers were analyzed, along with top-soil leachate and pore-water samples from aquitards. Stable oxygen (δ¹⁸O) and hydrogen isotopes, radiocarbon and hydrochemical analyses of the groundwater and pore-water samples were conducted to trace groundwater hydrological and hydrochemical processes and thereby understand the distribution and migration mechanism of F. The groundwater is recharged by meteoric precipitation through vapor condensation processes in the Tianshan Mountains. The F concentration in groundwater samples from this basin ranged from 0.11 to 48.15 mg/L (mean 2.56 mg/L). In 37 of the 90 groundwater samples, the F concentrations were above the safe level for drinking water. The F concentrations progressively increased with the residence time and well depths in the northwest of the alluvial-fluvial plain, where groundwater is overexploited for agricultural and domestic use. Positive correlations between F and sodium (Na)/calcium (Ca) indicate that the enrichment and migration of F are influenced by cation exchange processes under high-Na and alkaline pH conditions. The relationships between δ¹⁸O and F and chloride (Cl) concentrations were nonlinear due to leaching and mixing processes. This shows that vertical leaching by irrigation return flow and mixing with pore water are the dominant processes driving the migration of F in the groundwater flow system of MRB, in addition to geochemical processes.

[en] Highlights: • The S-enantiomer degraded more slowly than the R-enantiomer in single soil system. • The S-enantiomer exerted long-term strong inhibition on soil microbial functions. • Earthworms accelerated the degradation of enantiomers, especially the S-enantiomer. • Earthworms alleviated inhibition of S-enantiomer on soil microbial functions. • Earthworms evidently stimulated potential degraders in the S-enantiomer treatment. This study investigated the effects of earthworms on the enantioselective degradation of chloroacetamide herbicide acetochlor with soil microorganisms in repeatedly treated soils. The S-enantiomer degraded more slowly and exerted stronger inhibition on soil microbial functions than the R-enantiomer in single soil system. A synergistic effect was observed between soil microorganisms and earthworms that accelerated the degradation of both the enantiomers, particularly the highly toxic S-enantiomer, which resulted in the preferential degradation of S-enantiomer in soil-earthworm system. Earthworms stimulated five potential indigenous degraders (i.e. Lysobacter, Kaistobacter, Flavobacterium, Arenimonas, and Aquicell), induced two new potential degraders (i.e. Aeromonas and Algoriphagus), and also significantly strengthened the correlations among these seven dominant potential degraders and other microorganisms. Notably, the relative abundances of Flavobacterium and Aeromonas in soil treated with earthworms for S-enantiomer were higher than those for R-enantiomer. Furthermore, earthworms significantly stimulated overall soil microbial activity and improved three microbial metabolic pathways, and xenobiotics biodegradation and metabolism, signal transduction, cell motility, particularly for the S-enantiomer treatment with earthworms, which alleviated the strong inhibition of S-enantiomer on microbial community functions. This study confirmed that earthworms accelerated the degradation of the highly toxic acetochlor S-enantiomer in soil, providing a potential approach in chloroacetamide herbicide-polluted soil remediation.

[en] The long-term application of substantial amounts of fungicides and antibiotic-polluted organic manure (OM) in greenhouse has caused the co-existence of fungicides and antibiotics in soils. However, little is known about the effects of antibiotics on the persistence of fungicides in soils or their combined effects on soil enzyme activity. In this study, fungicide chlorothalonil (CTL) alone and in combination with antibiotic chlortetracycline (CTC) or ciprofloxacin (CIP) were repeatedly added to OM-amended soil to investigate the changes in the residual characteristics of CTL and in soil dehydrogenase and urease activity. The results showed that CTL rapidly dissipated in soils with the corresponding half-lives of 0.9–3.2, which initially increased, then decreased and finally stabilized with an increased treatment frequency. The dissipation of CTL was inhibited by CTC and CIP during the first several treatments. The soil dehydrogenase and urease activity in CTL-treated soils was inhibited during the first six treatments and then recovered afterwards. Compared with the OM-amended soil+CTL treatment, the OM-amended soil+CTL+CTC and OM-amended soil+CTL+CIP treatments had stronger inhibitory effects on soil enzyme activity during the first six repeated treatments but exhibited slight stimulating effects afterwards. Therefore, the results obtained in this study suggested that the long-term co-existence of CTL, CTC, and CIP altered the dissipation characteristics of CTL in soil and affected the soil enzyme activity levels. The prudent application of large and frequent of fungicides and OM-containing antibiotic residues in greenhouses should therefore be carefully considered in order to reduce the long-term combined pollution in soils.

[en] Highlights: • S-(+)-isomer enriched faster in earthworm than that of R-(-)-isomer • CYP450 and GST were superior to CarE in the detoxification of mandipropamid isomers • The DEGs in earthworms induced by S-(+)- isomer were greater than that by R-(-)-isomer • Bile secretion and thyroid hormone signaling pathways were significantly enriched • S-(+)-isomer may have a higher risk to earthworms than R-(-)-isomer As a novel chiral amide fungicide, the enantioselective behaviors of mandipropamid in the soil environment are unclear. Furthermore, there is a need to understand the stress response mechanisms of soil organisms exposed to mandipropamid isomers. Therefore, the selective bioaccumulation of mandipropamid isomers and detoxification mechanisms of earthworms (Eisenia fetida) were investigated in this study. Our results suggested that the enantioselective bioaccumulation of mandipropamid in earthworms occurred with the preferential enrichment of S-(+)-isomer. The activities of detoxification enzymes, such as cytochrome P450 (CYP450), glutathione-S-transferases (GST), and carboxylesterase (CarE), changed significantly upon exposure to S-(+)- and R-(-)-mandipropamid (particularly for CYP450 and GST). A transcriptome analysis revealed that more differentially expressed genes (DEGs) were observed under S-(+)-isomer exposure (15,798) than those under R-(-)-isomer exposure (12,222), as compared to the control group. These DEGs were mainly enriched in bile secretion and thyroid hormone signaling pathways, which were related to the detoxification process in earthworms. Moreover, the 20 DEGs, which exhibited the most profound changes (such as CYP2 and CYP3A4) in these pathways, were screened, clustered, and observed to be mainly involved in regulating the detoxification function of earthworm cells. These results indicated that detoxification systems played an essential role in the stress response to mandipropamid exposure. Additionally, earthworms were more sensitive to the stress induced by S-(+)-mandipropamid than that induced by R-(-)-mandipropamid. This is the first study to elucidate the mandipropamid detoxification mechanism of earthworms at the enantiomer level, which can be beneficial for remediating chiral pollutants.

[en] Highlights: • S-(+)-HEX exhibited higher toxicity to earthworms than R-(−)-HEX. • .HEX enantiomers had significant enantioselective degradation in artificial soil. • No significant difference was found in earthworm bioaccumulation between HEX enantiomers. • S-(+)-HEX induced more seriously oxidative stress than that of R-(−)-HEX. • S-(+)-HEX affected steriod biosynthesis, arachidonic acid metabolism and cell cycle. The enantioselective toxic effect and environmental behavior of chiral pesticides have attracted increasing research attention. In this study, the enantioselective toxicity and residues of hexaconazole (HEX) in earthworms (Eisenia fetida) were investigated. In the present study, significant enantioselective degradation characteristics were observed in artificial soil with the R-enantiomer preferentially degrading (p < 0.05); however, no significant enantioselective bioaccumulation was observed in the earthworms (p > 0.05). The acute toxicity of S-(+)-HEX was higher than that of R-(−)-HEX in earthworms, with 48-h LC₅₀ values of 8.62 and 22.35 μg/cm², respectively. At 25 mg/kg, enantiospecific induction of oxidative stress was observed in earthworms; moreover, S-(+)-HEX had a greater influence on the contents of malonaldehyde, cytochrome P450, and 8-hydroxy-2-deoxyguanosine than R-(−)-HEX. These results were consistent with those of the enrichment analysis of differentially expressed genes. The transcriptome sequencing results showed that S-(+)-HEX had a more significant influence on steroid biosynthesis, arachidonic acid metabolism, and cell cycle processes than R-(−)-HEX, leading to abnormal biological function activities. These results indicate that S-(+)-HEX may pose a higher risk to soil organisms than R-(−)-HEX. This study suggests that the environmental risk of chiral pesticides to nontarget organisms should be assessed at the enantiomeric level.