Dataset Information

Modeling historical budget for β-Hexachlorocyclohexane (HCH) in the Arctic Ocean: A contrast to α-HCH.

ABSTRACT: The historical annual loading to, removal from, and cumulative burden in the Arctic Ocean for β-hexachlorocyclohexane (β-HCH), an isomer comprising 5-12% of technical HCH, is investigated using a mass balance box model from 1945 to 2020. Over the 76 years, loading occurred predominantly through ocean currents and river inflow (83%) and only a small portion via atmospheric transport (16%). β-HCH started to accumulate in the Arctic Ocean in the late 1940s, reached a peak of 810 t in 1986, and decreased to 87 t in 2020, when its concentrations in the Arctic water and air were ∼30 ng m^-3 and ∼0.02 pg m^-3, respectively. Even though β-HCH and α-HCH (60-70% of technical HCH) are both the isomers of HCHs with almost identical temporal and spatial emission patterns, these two chemicals have shown different major pathways entering the Arctic. Different from α-HCH with the long-range atmospheric transport (LRAT) as its major transport pathway, β-HCH reached the Arctic mainly through long-range oceanic transport (LROT). The much higher tendency of β-HCH to partition into the water, mainly due to its much lower Henry's Law Constant than α-HCH, produced an exceptionally strong pathway divergence with β-HCH favoring slow transport in water and α-HCH favoring rapid transport in air. The concentration and burden of β-HCH in the Arctic Ocean are also predicted for the year 2050 when only 4.4-5.3 t will remain in the Arctic Ocean under the influence of climate change.

SUBMITTER: Yang PF

PROVIDER: S-EPMC9755237 | biostudies-literature | 2023 Apr

REPOSITORIES: biostudies-literature

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Modeling historical budget for β-Hexachlorocyclohexane (HCH) in the Arctic Ocean: A contrast to α-HCH.

Yang Pu-Fei PF Macdonald Robie W RW Hung Hayley H Muir Derek C G DCG Kallenborn Roland R Nikolaev Anatoly N AN Ma Wan-Li WL Liu Li-Yan LY Li Yi-Fan YF

Environmental science and ecotechnology 20221130

The historical annual loading to, removal from, and cumulative burden in the Arctic Ocean for β-hexachlorocyclohexane (β-HCH), an isomer comprising 5-12% of technical HCH, is investigated using a mass balance box model from 1945 to 2020. Over the 76 years, loading occurred predominantly through ocean currents and river inflow (83%) and only a small portion via atmospheric transport (16%). β-HCH started to accumulate in the Arctic Ocean in the late 1940s, reached a peak of 810 t in 1986, and decr ...[more]

PMID: 36531934

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Project description:Among sphingomonads, Sphingobium indicum B90A is widely investigated for its ability to degrade a manmade pesticide, γ-hexachlorocyclohexane (γ-HCH) and its isomers (α-, β-, δ-, and ε-HCH). In this study, complete genome of strain B90A was constructed using Single Molecule Real Time Sequencing (SMRT) and Illumina platform. The complete genome revealed that strain B90A harbors four replicons: one chromosome (3,654,322 bp) and three plasmids designated as pSRL1 (139,218 bp), pSRL2 (108,430 bp) and pSRL3 (43,761 bp). The study determined the precise location of lin genes (genes associated with the degradation of HCH isomers), for example, linA2, linB, linDER, linF, linGHIJ, and linKLMN on the chromosome; linA1, linC, and linF on pSRL1 and linDEbR on pSRL3. Strain B90A contained 26 copies of IS6100 element and most of them (15 copies) was found to be associated with lin genes. Duplication of several lin genes including linA, linDER, linGHIJ, and linF along with two variants of linE, that is, linEa (hydroquinone 1,2-dioxygenase) and linEb (chlorohydroquinone/hydroquinone 1,2-dioxygenase) were identified. This suggests that strain B90A not only possess efficient machinery for upper and lower HCH degradation pathways but it can also act on both hydroquinone and chlorohydroquinone metabolites produced during γ-HCH degradation. Synteny analysis revealed the duplication and transposition of linA gene (HCH dehydrochlorinase) between the chromosome and pSRL1, possibly through homologous recombination between adjacent IS6100 elements. Further, in silico analysis and laboratory experiments revealed that incomplete tyrosine metabolism was responsible for the production of extracellular brown pigment which distinguished strain B90A from other HCH degrading sphingomonads. The precise localization of lin genes, and transposable elements (IS6100) on different replicons now opens up several experimental avenues to elucidate the functions and regulatory mechanism of lin genes acquisition and transfer that were not completely known among the bacterial population inhabiting the HCH contaminated environment.

Project description:BACKGROUND: Sphingobium spp. are efficient degraders of a wide range of chlorinated and aromatic hydrocarbons. In particular, strains which harbour the lin pathway genes mediating the degradation of hexachlorocyclohexane (HCH) isomers are of interest due to the widespread persistence of this contaminant. Here, we examined the evolution and diversification of the lin pathway under the selective pressure of HCH, by comparing the draft genomes of six newly-sequenced Sphingobium spp. (strains LL03, DS20, IP26, HDIPO4, P25 and RL3) isolated from HCH dumpsites, with three existing genomes (S. indicum B90A, S. japonicum UT26S and Sphingobium sp. SYK6). RESULTS: Efficient HCH degraders phylogenetically clustered in a closely related group comprising of UT26S, B90A, HDIPO4 and IP26, where HDIPO4 and IP26 were classified as subspecies with ANI value >98%. Less than 10% of the total gene content was shared among all nine strains, but among the eight HCH-associated strains, that is all except SYK6, the shared gene content jumped to nearly 25%. Genes associated with nitrogen stress response and two-component systems were found to be enriched. The strains also housed many xenobiotic degradation pathways other than HCH, despite the absence of these xenobiotics from isolation sources. Additionally, these strains, although non-motile, but posses flagellar assembly genes. While strains HDIPO4 and IP26 contained the complete set of lin genes, DS20 was entirely devoid of lin genes (except linKLMN) whereas, LL03, P25 and RL3 were identified as lin deficient strains, as they housed incomplete lin pathways. Further, in HDIPO4, linA was found as a hybrid of two natural variants i.e., linA1 and linA2 known for their different enantioselectivity. CONCLUSION: The bacteria isolated from HCH dumpsites provide a natural testing ground to study variations in the lin system and their effects on degradation efficacy. Further, the diversity in the lin gene sequences and copy number, their arrangement with respect to IS6100 and evidence for potential plasmid content elucidate possible evolutionary acquisition mechanisms for this pathway. This study further opens the horizon for selection of bacterial strains for inclusion in an HCH bioremediation consortium and suggests that HDIPO4, IP26 and B90A would be appropriate candidates for inclusion.

Project description:BackgroundFluted pumpkin (Telfairia occidentalis) and amaranth (Amaranthus spp.) are common leafy vegetables produced and consumed in southwestern Nigeria. These vegetables attract insect pests which are controlled by pesticides that may have adverse impacts on human health.ObjectivesTo determine the levels of dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) pesticide residues in the two vegetables and evaluate the potential health risks associated with their consumption.MethodsThe pesticide residue levels were quantitatively and qualitatively determined using a gas chromatograph coupled with electron capture detector. Health risk assessment were performed using estimated average daily intake and hazard indices for two weight categories: children (16.7 kg) and adults (60 kg).ResultsThe results showed that delta-HCH, DDT and methoxychlor were predominantly detected in the two vegetables from both farms and markets. In amaranth, the mean concentration of methoxychlor, DDT and delta-HCH were 4.590 ± 2.774 mg/kg (dry weight (dw)), 0.757 ± 0.457 mg/kg (dw) and 0.577 ± 0.390 mg/kg (dw), respectively, while fluted pumpkin levels were 6.223 ± 2.489 mg/kg dw (methoxychlor), 0.504 ± 0.056 mg/kg dw (delta-HCH) and 0.486 ± 0.123 mg/kg dw (DDT). The levels of HCH and DDT residues were generally above the United Kingdom/European Commission maximum residue limit. The analysis of health risk estimates for non-carcinogenic risk revealed that for both vegetables, the hazard quotient for p, p' DDT and methoxychlor was >1 for both children and adults. The health risk estimates for carcinogenic risk revealed that hazard indices values were >1 for children for both vegetables and alpha-HCH had a hazard index >1 for adults for amaranth. This means the residue exceeds acceptable standard and present potential risk to consumers of these vegetables.ConclusionsThe results obtained from the present study indicate that consumption of amaranth contaminated with alpha-HCH could pose a carcinogenic risk for adult consumers. The consumption of the two vegetables could pose both non-carcinogenic and carcinogenic health risks to children and adults. Therefore, there is need for strict enforcement of regulations on pesticide usage to minimize human health risks.Competing interestsThe authors declare no competing financial interests.

Dataset Information

Modeling historical budget for β-Hexachlorocyclohexane (HCH) in the Arctic Ocean: A contrast to α-HCH.

Publications

Modeling historical budget for β-Hexachlorocyclohexane (HCH) in the Arctic Ocean: A contrast to α-HCH.

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