Application of combined QSAR-ICE models in calculation of hazardous concentrations for linear alkylbenzene sulfonate

Growth and physiological responses of submerged macrophytes to linear alkylbenzene sulfonate (LAS)

The potential toxic effects of linear alkylbenzene sulfonate (LAS), widely used in commercial detergents and cleaners, on submerged macrophytes remain unclear. We conducted a two-week exposure experiment to investigate LAS toxicity on five submerged macrophytes (four native and one exotic), focusing on their growth and physiological responses. The results showed that lower concentrations of LAS (< 5 mg/L) slightly stimulated the growth of submerged macrophytes, while higher doses inhibited it. Increasing LAS concentration resulted in decreased chlorophyll content, increased MDA content and POD activity, and initially increased SOD and CAT activities before declining. Moreover, Elodea nuttallii required a higher effective concentration for growth compared to native macrophytes. These findings suggest that different species of submerged macrophytes exhibited specific responses to LAS, with high doses (exceeding 5 ∼ 10 mg/L) inhibited plant growth and physiology. However, LAS may promote the dominance of surfactant-tolerant exotic submerged macrophytes in polluted aquatic environments.

Profound regional disparities shaping the ecological risk in surface waters: A case study on cadmium across China

The scientific advancement of water quality criteria (WQC) stands as one of the paramount challenges in ensuring the security of aquatic ecosystem. The region-dependent species distribution and water quality characteristics would impact the toxicity of pollutant, which would further affect the derivation of WQC across regions. Presently, however, numerous countries adhere to singular WQC values. The "One-size-fits-all" WQC value for a given pollutant may lead to either "over-protection" or "under-protection" of organisms in specific region. In this study, we used cadmium(Cd) pollution in surface waters of China as a case study to shed light on this issue. This study evaluated critical water quality parameters and species distribution characteristics to modify WQC for Cd across distinct regions, thus unveiling the geographical variations in ecological risk for Cd throughout China. Notably, regional disparities in ecological risk emerged a substantial correlation with water hardness, while species-related distinctions magnified these regional variations. After considering the aforementioned factors, the variation in long-term WQC among different areas reached 84-fold, while the divergence in risk quotient extended to 280-fold. This study delineated zones of both heightened and diminished ecological susceptibility of Cd, thereby establishing a foundation for regionally differentiated management strategies.

Prediction of freshwater ecotoxicological hazardous concentrations of major surfactants using the QSAR-ICE-SSD method

Synthetic surfactant products are continuously released into the aquatic environment in large quantities, posing a burden on ecosystems as a "pseudo-persistent" organic pollutant. Threshold derivation for protecting aquatic ecosystems is challenging due to the various homologous components of surfactants. In this study, five commercially available products were chosen as representative major types of surfactants. Corresponding quantitative structure-activity relationships (QSAR) were screened and subsequently combined with interspecific correlation estimation (ICE) to develop species sensitivity distributions (SSDs) for each component. Then, the 5th percentile hazard concentrations (HC5s) were calculated. The results indicated that the developed QSAR-ICE models demonstrated good toxicity prediction performance. The HC5 of each component showed a negatively correlation with alkyl chain length and a positive correlation with the amount of ethylene oxide. The HC5s of surfactants correlate with variations in their charged properties. Quaternary ammonium compounds (QAC) exhibited the lowest HC5s (8.5 ± 18.3 μg/L), followed by alcohol ethoxylates (AE), linear alkylbenzene sulfonates (LAS), and alcohol ethoxylated sulfates (AES); and alkyl oxide (AO) exhibited the highest HC5s (15784.2 ± 21552.6 μg/L). For cationic surfactants, the HC5s in the invertebrates were significantly lower than those in the fish; conversely, for anionic surfactants, the opposite was true, indicating a difference in the toxic mechanisms of surfactants with different charged properties across species taxa. Additionally, among invertebrates, shellfish demonstrated heightened sensitivity to surfactants, owing to their high accumulation and low metabolism of pollutants. Salmoniformes were the most sensitive among all species, indicating the necessity of prioritizing these species for aquatic ecological conservation in surfactant-contaminated waters.

PMS coupled Mn(II) mediated electrochemistry processes (E-Mn(II)-PMS) on the efficient RB19 wastewater treatment: Focus on the regulation and reinforcement of Mn(III)/Mn(II)

Dye wastewater, represented by reactive blue 19 (RB19), severely threatens the aquatic ecological environment and human health, such that an efficient RB19 wastewater treatment technology should be urgently developed. Based on manganese ion-mediated electrochemistry, PMS was introduced to develop a novel electrocatalytic system (E-Mn(II)-PMS) that can efficiently remove and degrade RB19. The synergistic effect between E, Mn(II), and PMS was verified in this study through comparative experiments of a wide variety of systems. The removal efficiency of RB19 reached 95.1% in 50 min under reasonable power consumption (3.29 kWh/m3). Moreover, the effects exerted by different operating conditions (e.g., initial pH, current density, RB19 concentration, Mn(II) concentration, as well as PMS concentration) and water matrix on the degradation efficiency of RB19 were explored through single factor experiments. The active oxidation species (ROS) and their contribution rate for the degrading and removing RB19 were studied through quenching experiments, EPR experiments, TMT-15 metal capture experiments, as well as PP complexation experiments. The role played by non-free radicals took on critical significance in the oxidation removal of RB19, which comprised direct electro oxidation, Mn(III) oxidation, and 1O2 oxidation. The enhancement effect of free radicals (SO4·- and HO∙) was not sufficiently significant, with a low degree of contribution. The oxidation effect of the anode facilitated the conversion of Mn (II) to Mn (III), which was employed in PMS for expediting the production of 1O2. The reduction effect of the cathode blocked the production of Mn (IV) as a side reaction, such that the continuous circulation of manganese ions between divalent and trivalent was promoted. Meanwhile, the cathode reacted with PMS to generate a small part of SO4·- and HO∙. In addition, the reaction active site of RB19 was predicted, and a possible degradation pathway was proposed in accordance with the mass spectrometry results and the DFT calculation. As revealed by the results of the QSAR analysis and the plant culture experiments, the biological toxicity of RB19 was markedly reduced after the sample was administrated with E-Mn(II)-PMS. E-Mn(II)-PMS-mediated electrochemical technology displays several advantages (e.g., high efficiency, low consumption, recyclability, wide pH window, and strong applicability) while showing promising market development and utilization for treating dye wastewater.

Linear alkylbenzene sulfonate threats to surface waters at the national scale: A neglected traditional pollutant

Freshwater biodiversity and ecosystem services might decline due to exposure to chemicals. However, researchers have devoted much attention to the potential risks of emerging contaminants, while placing less effort on historical pollutants, such as the surfactant, linear-alkylbenzene-sulfonate (LAS), which is a major component of widely used synthetic detergents worldwide. In this study, a multilevel risk assessment approach was used to assess risks posed by LAS to aquatic organisms, on a wide spatial scale, based on various assessment endpoints. Additionally, bottom-up approaches were used to assess contributions of LAS source discharges to aquatic environments. Concentrations of LAS in surface waters of China ranged from less than the limit of detection to 14,200 μg/L. The predicted no effect concentration (PNEC) based on adverse effects on reproduction is 15 μg/L, which is slightly less than the PNEC based on other endpoints. 99% of surface waters in Chaohu Lake and the Hai River (Ch: Haihe) were predicted to pose a risk to growth of aquatic organisms, with a protection threshold of 5% of species (HC₅). Discharges of LAS were estimated using activity data and emission factors for 280 major cities in the basin. Rural domestic sources were the main source of LAS to surface waters. These outcomes provided a process for developing comprehensive management and control approaches to help researchers and policymakers effectively manage water resources affected by increasing concentrations of LAS.

Water quality criteria and ecological risk assessment of lead (Pb) in China considering the total hardness of surface water: A national-scale study

Site-specific water quality criteria considering hydrochemical conditions are needed for zoning control of environmental risks. However, the differences in water quality parameters between regions have not been fully considered in the current research on water quality criteria and risk assessment of lead. In this study, lead concentration and total hardness (TH) data of surface water in 13 major river basins and 31 administrative regions in China were collected. Based on the normalization of the TH of the toxicity data, the short-term and long-term water quality criteria of lead in China's surface water in the specific TH condition (100 mg/L) were derived using the species sensitivity distribution method, which were 90.7 μg/L and 2.1 μg/L, respectively. Furthermore, this study provided general derivation formulas for the water quality criteria based on the TH of surface water and obtained the site-specific criteria for different regions/basins in China. On this basis, an ecological risk assessment considering the TH was proposed for the first time. The results showed that there was a clear risk of lead in the Pearl River Basin and the rivers in Zhejiang-Fujian. The southern coastal provinces were at an unacceptable risk level, although the lead concentrations in the surface water were medium; the opposite was true in northern China, which meant that a high concentration of lead did not necessarily pose a high ecological risk and about 25 % of the variation in the predicted risk can be explained by the TH in Monte Carlo simulation.