Synergistic detoxification efficiency and mechanism of triclocarban degradation by a bacterial consortium in the liver-gut-microbiota axis of zebrafish (Danio rerio)

Triclocarban (TCC), an emerging organic contaminant, poses a potential threat to human health with long-term exposure. Here, Rhodococcus rhodochrous BX2 and Pseudomonas sp. LY-1 were utilized to degrade TCC at environmental related concentrations for enhancing TCC biodegradation and investigating whether the toxicity of intermediate metabolites is lower than that of the parent compound. The results demonstrated that the bacterial consortium could degrade TCC by 82.0% within 7 days. The calculated 96 h LC50 for TCC, as well as its main degradation product 3,4-Dichloroaniline (DCA) were 0.134 mg/L and 1.318 mg/L respectively. Biodegradation also alleviated histopathological lesions induced by TCC in zebrafish liver and gut tissues. Liver transcriptome analysis revealed that biodegradation weakened differential expression of genes involved in disrupted immune regulation and lipid metabolism caused by TCC, verified through RT-qPCR analysis and measurement of related enzyme activities and protein contents. 16 S rRNA sequencing indicated that exposure to TCC led to gut microbial dysbiosis, which was efficiently improved through TCC biodegradation, resulting in decreased relative abundances of major pathogens. Overall, this study evaluated potential environmental risks associated with biodegradation of TCC and explored possible biodetoxification mechanisms, providing a theoretical foundation for efficient and harmless bioremediation of environmental pollutants.

Iron minerals: A frontline barrier against combined toxicity of microplastics and arsenic

The coexistence of microplastics (MPs) and arsenic (As) in terrestrial ecosystems presents challenges to controlling soil pollution and performing environmental risk assessments. In this study, the interactions among As, polystyrene MPs, and goethite in porous media were investigated and the individual and combined toxicities of MPs and As on wheat germination were evaluated. An additional experiment was conducted to assess the mitigating effect of goethite on the toxicity of the two contaminants. The results showed that the presence of MPs reduced As accumulation in wheat and decreased the acute lethal toxicity of As pollutants (the half-lethal concentration of As during wheat germination increased by 68.21%). However, MPs exhibited inhibitory effects on wheat germination and served as carriers to promote the migration of As within the plant body. The addition of goethite mitigated both individual and combined toxicities and further increased the half-lethal concentration for the combined pollution of As and MPs by 39.48%. This was primarily attributed to the adsorption and immobilization of arsenate and MPs on the medium and root surfaces. In our study, goethite reduced soluble As by 48.29% under the combined pollution scenarios and formed iron plaques on wheat roots, effectively obstructing pollutant entry. Thus, iron minerals serve as pioneering barriers to combined toxicity. Our findings contribute to the understanding of the combined toxicity of MPs and As in crops and offer potential strategies for managing combined pollution.

Bioupgrading of the aqueous phase of pyrolysis oil from lignocellulosic biomass: a platform for renewable chemicals and fuels from the whole fraction of biomass

Pyrolysis, a thermal decomposition without oxygen, is a promising technology for transportable liquids from whole fractions of lignocellulosic biomass. However, due to the hydrophilic products of pyrolysis, the liquid oils have undesirable physicochemical characteristics, thus requiring an additional upgrading process. Biological upgrading methods could address the drawbacks of pyrolysis by utilizing various hydrophilic compounds as carbon sources under mild conditions with low carbon footprints. Versatile chemicals, such as lipids, ethanol, and organic acids, could be produced through microbial assimilation of anhydrous sugars, organic acids, aldehydes, and phenolics in the hydrophilic fractions. The presence of various toxic compounds and the complex composition of the aqueous phase are the main challenges. In this review, the potential of bioconversion routes for upgrading the aqueous phase of pyrolysis oil is investigated with critical challenges and perspectives.

The environmental fate of graphene oxide in aquatic environment-Complete mitigation of its acute toxicity to planktonic and benthic crustaceans by algae

Graphene oxide (GO) as the most studied hydrophilic graphene derivative can be deployed in a broad spectrum of environmental technologies opening the issue of its ecotoxicity. Nevertheless, the information about its behavior in complex aquatic environment is still not sufficient. Here, we studied the interaction of three differently oxidized GO systems with planktonic and benthic crustaceans. By standard toxicity tests, we observed the importance of feeding strategy as well as the surface oxidation of GO with respect to GO's ecotoxicity. However, to gain a clearer insight into GO's environmental fate, we introduced a pre-treatment with algae as the most common source of food for crustaceans. Such an adjustment mimicking the conditions in real aquatic ecosystems resulted in complete mitigation of acute toxicity of GOs to all organisms and, more importantly, to the eradication of oxidative stress caused by GOs. We argue, that the pre-exposition of food is a crucial factor in GO's overall environmental fate, even though this fact has been completely neglected in recent studies. These experiments proved that GO is not a hazardous material in complex aquatic environments because its acute toxicity can be successfully mitigated through the interaction with algae even at very high concentrations (25 mg/L).

Application of seven different clay types in sorbent-modified biodegradability studies with cationic biocides

The cationic surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPC) can exert inhibitory effects on micro-organisms responsible for their biodegradation. However, under environmentally relevant exposure scenarios the presence of and sorption to organic and inorganic matter can lead to significant reduction of inhibitory effects. In our studies we investigated silica gel and seven clays as inert sorbents to mitigate these inhibitory effects in a 28 day manometric respirometry biodegradation test. CTAB was not inhibitory to the used inoculum, but we did observe that seven out of eight sorbents increased maximum attainable biodegradation, and four out of eight decreased the lag phase. The strongly inhibitory effect of CPC was successfully mitigated by most sorbents, with five out of eight allowing >50% biodegradation within 28 days. Results further indicate that bioaccessibility of the sorbed fractions in the stirred manometric test systems was higher than in calmly shaken headspace test systems. Bioaccessibility might also be limited depending on characteristics of test chemical and sorbent type, with montmorillonite and bentonite apparently providing the lowest level of bioaccessibility with CPC. Clay sorbents can thus be used as environmentally relevant sorbents to mitigate potential inhibitory effects of test chemicals, but factors that impede bioaccessibility should be considered. In addition to apparently increased bioaccessibility due to stirring, the automated manometric respirometry test systems give valuable and highly cost-effective insights into lag phase and biodegradation kinetics; information that is especially relevant for test chemicals of gradual biodegradability.

Sorbent-modified biodegradation studies of the biocidal cationic surfactant cetylpyridinium chloride

Biodegradability studies for the cationic surfactant cetylpyridinium chloride (CPC) are hampered by inhibitory effects on inoculum at prescribed test concentrations (10-20 mg organic carbon/L). In this study, we used ¹⁴C labeled CPC in the 28 d Headspace Test (OECD 310) and demonstrated that CPC was readily biodegradable (10->60% mineralization within a 10 day window) at test concentrations 0.006-0.3 mg/L with CPC as single substrate. Biodegradation efficiency was comparable over this concentration range. CPC inhibited degradation at 1 mg/L and completely suppressed inoculum activity at 3 mg/L. In an extensive sorbent modified biodegradation study we evaluated the balance between CPC bioaccessibility and toxicity. A non-inhibitory concentration of 0.1 mg/L CPC was readily biodegradable with 83% sorbed to SiO₂, while biodegradation was slower when 96% was sorbed. SiO₂ mitigated inhibitory effects of 1 mg/L CPC, reaching >60% biodegradation within 28 d; inhibitory effects were also mitigated by addition of commercial clay powder (illite) but this was primarily reflected by a reduced lag phase. At 10 mg/L CPC SiO₂ was still able to mitigate inhibitory effects, but bioaccessibility seemed limited as only 20% biodegradation was reached. Illite limited bioaccessibility more strongly and was not able to sustain biodegradation at 10 mg/L CPC.

Toxicity mitigation and bioaccessibility of the cationic surfactant cetyltrimethylammonium bromide in a sorbent-modified biodegradation study

Biodegradation potential of cationic surfactants may be hampered by inhibition of inoculum at concentrations required to accurately measure inorganic carbon. At >0.3 mg/L cetyltrimethylammonium bromide (CTAB) negatively impacted degradation of the reference compound aniline. We used silicon dioxide (SiO₂) and illite as inorganic sorbents to mitigate toxicity of CTAB by lowering freely dissolved concentrations. In an OECD Headspace Test we tested whether 16.8 mg/L CTAB was readily biodegradable in presence of two concentrations of SiO₂ and illite. SiO₂ adsorbed 85% and 98% CTAB, resulting in concentrations of 2.5 and 0.34 mg/L, mineralized to CO₂ >60% within 16 and 23 d, respectively. With 89% and 99% sorbed to illite, 60% mineralization was reached within 9 and 23 d, respectively. However, higher sorbent concentrations increased time needed to reach >60% mineralization. Thus, desorption kinetics likely decreased bioaccessibility. It is therefore essential to determine appropriate concentrations of mitigating sorbents to render a Headspace Test based on carbon analysis suitable to determine ready biodegradability of compounds which might inhibit inoculum. This would avoid use of expensive radiolabeled compounds. However, high sorbent concentrations can reduce bioaccessibility and limit degradation kinetics, particularly for relatively toxic substances that require strong mitigation.

Role of plant growth-promoting Ochrobactrum sp. MC22 on triclocarban degradation and toxicity mitigation to legume plants

Triclocarban (TCC) is an emerging and persistent pollutant once released into environment. In this study, TCC-degrading Ochrobactrum sp. MC22, was isolated and characterized. This is the first report on plant-growth promoting bacterium with versatile capability of TCC degradation under aerobic and anaerobic conditions. The aerobic degradation of TCC occurred completely of which the kinetic analysis revealed a non-self-inhibitive substrate effect, and broad-concentration-range degradation efficiency (ranging from 0.16-30mgL-1). Anaerobic TCC degradation was feasible, but was significantly enhanced up to 40-50% when ferric, or acetate was provided as electron donor, or acceptor, respectively. TCC biodegradation under both conditions was proposed to initially occur through hydrolysis leading to transient accumulation of chloroanilines, which could be completely metabolized and detoxified. With concern on TCC adverse effect to plants, role of MC22 on toxicity mitigation was investigated using two legume plants: Vigna radiata and Glycine max (L.) Merr. Upon TCC exposure, damage of both plant structures, especially root system was observed, but was substantially mitigated by MC22 bioaugmentation. This study not only provides thorough TCC degradation characteristic and kinetics of MC22, but also suggests a potential role of this bacterial strain for a rhizoremediation in crop area with TCC contamination.