Effects of heavy metals and metalloids on the biodegradation of organic contaminants.

Heavy metals and metalloids (HMMs) inhibit the biodegradation of organic pollutants. The degree of inhibition depends not only on the concentration and bioavailability of HMMs but also on additional factors, such as environmental variables (e.g., inorganic components, organic matter, pH, and redox potential), the nature of the metals, and microbial species. Based on the degradation pattern and metal concentrations causing half biodegradation rate reductions (RC50s), the inhibition of biodegradation was: Hg2+, As2O3 > Cu2+, Cd2+, Pb2+, Cr3+ > Ni2+, Co2+ > Mn2+, Zn2+ > Fe3+. Four patterns were observed: inhibition increases with increasing metal concentration; low concentrations stimulate, while high concentrations inhibit; high concentrations inhibit less; and mild inhibition remains constant. In addition, metal ion mixtures have more complex inhibitory effects on the degradation of organic pollutants, which may be greater than, similar to, or less than that of individual HMMs. Finally, the inhibitory mechanism of HMMs on biodegradation is reviewed. HMMs generally have little impact on the biodegradation pathway of organic pollutants for bacterial strains. However, when pollutants are biodegraded by the community, HMMs may activate microbial populations harbouring different transformation pathways. HMMs can affect the biodegradation efficiency of organic pollutants by changing the surface properties of microbes, interfering with degradative enzymes, and interacting with general metabolism.

Use of nanoparticle-coated bacteria for the bioremediation of organic pollution: A mini review.

Nanoparticle (NP)-coated (immobilized) bacteria are an effective method for treating environmental pollution due to their multifarious benefits. This review collates a vast amount of existing literature on organic pollution treatment using NP-coated bacteria. We discuss the features of bacteria, NPs, and decoration techniques of NP-bacteria assemblies, with special attention given to the surface modification of NPs and connection mechanisms between NPs and cells. Furthermore, the performance of NP-coated bacteria was examined. We summarize the factors that affect bioremediation efficiency using coated bacteria, including pH, temperature, and agitation, and the possible mechanisms involving them are proposed. From future perspectives, suitable surface modification of NPs and wide application in real practice will make the NP-coated bacterial technology a viable treatment strategy.

Combined effects of vehicles and waste incineration on urban air halogenated and parent polycyclic aromatic hydrocarbons.

Traffic emissions and waste incineration are the main sources of PAHs in urban atmosphere, but their spatially superimposed effects are currently unclear. This study assessed the spatial distribution of PAHs and HPAHs concentrations in the atmosphere of Shenzhen by simulating the spatial and temporal dispersion of PAHs and HPAHs emissions from on-road vehicles and municipal solid waste incinerators (MSWIs). Generally, the concentrations of PAHs and HPAHs were higher on workdays than on weekends due to higher traffic volumes, while the prevailing wind direction of the northeast could cause more widespread dispersion of PAHs and HPAHs within Shenzhen's atmosphere. After superimposing the spatial distribution of pollutants emitted by vehicles and MSWIs, PAHs within 1000 m downwind of MSWIs are mainly contributed by MSWIs and beyond 1000 m by vehicles. The cancer risk values induced by exposure to PAHs and HPAHs via inhalation in Shenzhen were below the acceptable risk level for males and females in each age group, while adults faced the highest cancer risk, followed by adolescents and children. However, spatially, the cancer risk values were above the priority risk level for adult males in localized high-traffic areas in Futian and Luohu districts.

Photodegradation of phthalic acid esters under simulated sunlight: Mechanism, kinetics, and toxicity change.

The photodegradation of two phthalic acid esters (PAEs), dimethyl phthalate (DMP) and di-n-octyl phthalate (DOP), under simulated sunlight in aqueous or organic phases (n-hexane (HEX) and dichloromethane (DCM)) was investigated. The mean photodegradation rates were ranked by half-lives as follows: DOP in DCM (3.77 h) < DMP in DCM (9.62 h) < DOP in H2O (3.99 days) < DMP in H2O (19.2 days) < DOP in HEX (21.0 days) < DMP in HEX (>30 days). Compound-specific stable isotope analysis (CSIA) combined with intermediate analysis was employed to explore the involved initial photoreaction mechanism. C-O bond cleavage, chlorine radical adduction to the aromatic ring, competing reactions of chlorine radical adduction to the aromatic ring and side chain, and a singlet oxygen-mediated pathway were mainly responsible for initial photodegradation mechanism of PAEs in H2O, DMP in DCM, DOP in DCM, and DOP in HEX, respectively. Furthermore, distinct isotope fractionation patterns of PAEs photodegradation open the possibility of using CSIA to differentiate the involved solvents in the field. More toxic and recalcitrant intermediates emerged during the photodegradation of DMP in DCM, while the risk to human health was reduced during the photochemical transformation of DOP in organic solvents.

A 2D CSIA-based math method to quantify degradation rate by C-H bond breaking.

Compound-specific isotope analysis has been demonstrated to be a powerful tool for the assessment of in situ pollutant degradation. Enrichment factor, an essential and prerequisite parameter, could be determined under simulated control laboratory in advance. However, different microbial community composition and substrate availability may significantly affect the accuracy of simulated enrichment factor. Here, a modified mathematic method of two dimensional is proposed to quantify the extent of pollutant degradation involving the break of carbon and hydrogen bond. In this new model, the laboratory cultures used to determine carbon or hydrogen enrichment factors in advance could be canceled and the key point to assess the extent of biodegradation is only determining the value of Λri (dual C-H isotope slope calculated with a self-modified model) in the field investigation. As a new and convenient method, this math model greatly facilitates the investigation of pollutant degradation extent under field conditions. Two approaches are applied to evaluate the proposed model. With our model, the estimated results based on C isotope are consistent with those measured values, while those based on H isotope are unsatisfactory. This can be attributed to the differences in accuracy of C-H isotope determinations. Overall, enrichment factors and biodegradation rates calculated with the proposed model are comparable with those measured figures.

Anthropogenic influences in a rapidly urbanizing area using linear alkylbenzenes and polycyclic aromatic hydrocarbons as tracers.

Environmental molecular markers can be used to understand the sources, transport, and fate of pollutants. Furthermore, they can also be applied to assess the influences of anthropogenic activities and elucidate urbanization from different perspectives. In this study, the potential of linear alkylbenzenes (LABs) and polycyclic aromatic hydrocarbons (PAHs) as chemical indicators of urbanization was examined first. Overall, the concentrations of LABs and PAHs ranged from 5.49-148 ng/g (mean: 15.6, median: 9.33) and 3.61-4878 ng/g (mean: 181, median: 71.3), respectively. Owing to the different sources and input methods of these two substances in soil, the area-weighted median values for LABs were more suitable to assess the magnitude of contamination on the administrative scale. For PAHs, the average values were more practical. LAB (consumption-induced pollutants) and PAH (production-induced pollutants) concentrations exhibited good correlations with some indices for residential daily life and industrialization, which indicated that soil can be utilized to reveal multidimensional urbanization-environment relationships. Two different patterns, the inverted U-shaped pattern and the upward pattern, were employed to simulate the environment-urbanization relationships in Shenzhen, China, which indicated that raising the standard of living or industrialization had created different soil pollution. The environmental quality demand was more difficult to meet by changing the energy structure than by improving infrastructure.

A modified method to calculate dual-isotope slopes for the natural attenuation of organic pollutants in the environment.

Two-dimensional compound-specific isotope analysis has become a powerful tool for distinguishing reaction mechanisms. Lambda (Λ), an essential and important parameter for processing two-dimensional isotope fractionation data, exhibits values specific to a reaction mechanism. In the present article, we modified the existing algorithms for calculation of lambdas based on a review of current methods. Specifically, by regressing [(1000+δE0,2)*(n1*x2)*ΔδEbulk,1] versus [(1000+δE0,1)*(n2*x1)*ΔδEbulk,2] by the York method, a novel method was developed to calculate Λs. The improved method eliminates both the influence of the nonreacting position and the initial isotope signatures. Furthermore, this method retains the advantages of a two-dimensional isotope plot, which eliminates contributions from commitment to catalysis, does not require determination of the fraction of remaining substrate, and can be constructed even from field data. Additionally, the one-sample t test is applied to generate a 95% confidence interval of the dataset of Λris for various reaction mechanisms. The ranges of 5.67-24.8, 8.54-9.80, 0.51-8.35, 25.2-36.8, and 7.09-21.9 are applicable for the oxidation of C-H bonds (ZC=1, ZH=3; ZC and ZH are the number of indistinguishable carbon and hydrogen atoms in intramolecular competition, respectively), oxidation of C-H bonds (ZC=1, ZH=4), aerobic biodegradation of benzene (ZC=6, ZH=6), methanogenic or sulfate-reducing biodegradation of benzene (ZC=6, ZH=6), and nitrate-reducing biodegradation of benzene (ZC=6, ZH=6). The accumulation and correction of these values will make the data measured in the field easier to interpret.