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

Evaluation of co-foaming agents for enhanced removal of per-and polyfluoroalkyl substances (PFAS) by foam fractionation

Foam fractionation has emerged as a leading method to remove per- and polyfluoroalkyl substances (PFAS) from impacted aqueous matrices due to the low cost and rapid PFAS removal. Although foam fractionation has been shown to efficiently remove long-chain PFAS, cationic co-foaming agents are often necessary to improve the removal of short-chain PFAS. However, many of the best performing co-surfactants used for short-chain PFAS removal, such as cetyltrimethylammonium bromide (CTAB), are of concern due to their potential toxicity and low biodegradability. The objective of this study was to evaluate the performance of lower-toxicity co-foaming agents for enhanced removal of both long-chain and short-chain PFAS compounds. Six candidate co-foaming agents were tested in a laboratory-scale foam fractionation system that consisted of a 60-cm acrylic column equipped with a 0.5-μm air diffusor, injection and sampling ports, and a vacuum-assisted foam collection reservoir. Based on the results of experiments conducted using water containing long- and short-chain PFAS, a naturally derived zwitterionic surfactant derived from Shea butter was identified as the most promising alternative co-foaming agent. Subsequent experiments demonstrated that the shea butter derived surfactant (SBDS) performance was improved by lowering the pH to 3, and under these conditions, SBDS was able to remove greater than 99.5 % of the PFAS from groundwater collected from AFFF-impacted military installations. These findings demonstrate the efficacy of a low-toxicity, biodegradable co-foaming agent as a replacement for traditional cationic surfactants, which are known to be toxic and persistent in the environment.

Lipid-coated gold nanorods for photoimmunotherapy of primary breast cancer and the prevention of metastasis

Nanomedicines hold promise for the treatment of various diseases. However, treating cancer metastasis remains highly challenging. In this study, we synthesized gold nanorods (AuNRs) containing (α-GC), an immune stimulator, for the treatment of primary cancer, metastasis, and recurrence of the cancer. Therefore, the AuNR were coated with lipid bilayers loaded with α-GC (α-LA). Upon irradiation with 808 nm light, α-LA showed a temperature increase. Intra-tumoral injection of α-LA in mice and local irradiation of the 4T1 breast cancer tumor effectively eliminated tumor growth. We found that the presence of α-GC in α-LA activated dendritic cells and T cells in the spleen, which completely blocked the development of lung metastasis. In mice injected with α-LA for primary breast cancer treatment, we observed antigen-specific T cell responses and increased cytotoxicity against 4T1 cells. We conclude that α-LA is promising for the treatment of both primary breast cancer and its metastasis.

NIR-responsive porous gold nanorod dispersed in a 3D gelatin scaffold for stimulus-responsive drug release and synergistic therapy

Biodegradable porous nanomaterials have emerged as a promising avenue for tumor drug delivery owing to their capacity to encapsulate large quantities of drugs and their compatibility with biological systems.

Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences

This review aims to provide an overview of the sources and reactions of persistent organic pollutants (POPs) and surfactants in soil and sediments, the surfactant-enhanced solubilisation of POPs, and the unintended consequences of surfactant-induced remediation of soil and sediments contaminated with POPs. POPs include chemical compounds that are recalcitrant to natural degradation through photolytic, chemical, and biological processes in the environment. POPs are potentially toxic compounds mainly used in pesticides, solvents, pharmaceuticals, or industrial applications and pose a significant and persistent risk to the ecosystem and human health. Surfactants can serve as detergents, wetting and foaming compounds, emulsifiers, or dispersants, and have been used extensively to promote the solubilization of POPs and their subsequent removal from environmental matrices, including solid wastes, soil, and sediments. However, improper use of surfactants for remediation of POPs may lead to unintended consequences that include toxicity of surfactants to soil microorganisms and plants, and leaching of POPs, thereby resulting in groundwater contamination.

Insights into capture-inactivation/oxidation of antibiotic resistance bacteria and cell-free antibiotic resistance genes from waters using flexibly-functionalized microbubbles

The spread of antibiotic resistance in the aquatic environment severely threatens the public health and ecological security. This study investigated simultaneously capturing and inactivating/oxidizing the antibiotic resistant bacteria (ARB) and cell-free antibiotic resistance genes (ARGs) in waters by flexibly-functionalized microbubbles. The microbubbles were obtained by surface-modifying the bubbles with coagulant (named as coagulative colloidal gas aphrons, CCGAs) and further encapsulating ozone in the gas core (named as coagulative colloidal ozone aphrons, CCOAs). CCGAs removed 92.4-97.5% of the sulfamethoxazole-resistant bacteria in the presence of dissolved organic matter (DOM), and the log reduction of cell-free ARGs (particularly, those encoded in plasmid) reached 1.86-3.30. The ozone release from CCOAs led to efficient in-situ oxidation: 91.2% of ARB were membrane-damaged and inactivated. In the municipal wastewater matrix, the removal of ARB increased whilst that of cell-free ARGs decreased by CCGAs with the DOM content increasing. The ozone encapsulation into CCGAs reinforced the bubble performance. The predominant capture mechanism should be electrostatic attraction between bubbles and ARB (or cell-free ARGs), and DOM enhanced the sweeping and bridging effect. The functionalized microbubble technology can be a promising and effective barrier for ARB and cell-free ARGs with shortened retention time, lessened chemical doses and simplified treatment unit.

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.