Study on the Joint Toxicity of Multi-component Mixtures of Quaternary Ammonium Compounds

Pollutants generally exist as mixtures in the environment. Their cumulative toxicity and toxicity interactions are potential risks. Therefore, this study aimed to examine the variation of joint toxicity of a multi-component mixture system, which consisted of six common quaternary ammonium salt surfactants in the environment, on Vibrio qinghaiensis sp.-Q67 (Q67). Vibrio qinghaiensis sp. -Q67 (Vqin-Q67) is a freshwater luminescent bacterium that continuously emits blue-green light (485 nm). The bacterium has been widely used for detecting toxic contaminants. In the mixture system, the luminescent toxicity of each component of the mixture to Q67 was determined by the microplate toxicity analysis method, and the toxicity interaction of the mixture was determined by the toxicity unit method (TU). The combined toxicity of the mixture system was investigated from four aspects, including the number of components, key components, concentration (toxicity) ratio, and exposure time. The results showed that the combined toxic effect of the same mixture system tends to be an additive effect with the increase of the number of components. The combined toxicity of the mixture system was close to that of the key components. Antagonism was presented in the equal toxicity mixture, while synergism was presented in the non-equal toxicity mixture. The combined toxic effect of the multi-component mixture system was not only related to the concentration of the pollutant but also related to the exposure time of the pollutant.

Chlorpyrifos and Dichlorvos in Combined Exposure Reveals Antagonistic Interaction to Freshwater Fish Mrigal, Cirrhinus mrigala

Toxicity imposed by organophosphate pesticides to the freshwater cultivable fish species mrigal (Cirrhinus mrigala) was assessed under laboratory conditions. Healthy juveniles were exposed to chlorpyrifos, dichlorvos, and their equitoxic mixture in geometric series. Median lethal concentrations of chlorpyrifos were found to be 0.906 (0.689–1.179), 0.527 (0.433–0.633), 0.435 (0.366–0.517) and 0.380 (0.319–0.450) mg/L and dichlorvos were found to be 38.432 (33.625–47.866), 22.477 (19.047–26.646), 12.442 (9.619–14.196) and 11.367 (9.496–13.536) mg/L after 24 h, 48 h, 72 h and 96 h of exposure respectively. Surprisingly, the joint toxicity of these organophosphates in the binary mixture was less than additive during most of the exposure periods. Behavioral changes exhibited by pesticide exposed fish were elevated opercular beatings, loss of equilibrium, loss of schooling behavior, aggregating at corners of the test chamber, slight color changes, surplus mucus secretion, and sudden and rapid body movements before death. Such behavioral studies can be applied as a non-invasive bio-monitoring tool for water quality assessment for fish growth and development. Despite the same mode of action of both pesticides, the antagonistic action in the binary mixture is an interesting outcome of this research that requires further investigation for a lucid understanding of the joint toxicity mechanism of such pesticides.

Separate and combined effects of cadmium(Cd) and nonylphenol(NP) on growth and antioxidative enzymes in Hydrocharis dubia (Bl.) Backer

Cadmium (Cd) is listed as a priority pollutant, and nonylphenol(NP) is a common organic pollutant in water environment. However, the ecological risks of combined pollution of Cd and NP have not been fully elucidated. In this study, the effects of Cd (0.01, 0.1, 0.5, 1, 5 mg/L), NP (0.1, 0.5, 1, 5, 10 mg/L) and Cd-NP (0.01 + 0.1, 0.01 + 1.0, 0.5 + 0.1, 0.5 + 1.0, 5 + 0.1, 5 + 1.0 mg/L) on growth and physiology of Hydrocharis Dubia (Bl.) Backer were studied. The results showed that the toxicity of H. dubia showed a dose-dependent effect. Growth level and chlorophyll contents of H. dubia induced by NP stress alone showed a certain toxicant excitatory effect. It meant that low concentrations of toxins promote plants growth, high concentrations of toxins inhibit plants growth. The increase of H2O2 content and the decrease of soluble protein content in the plant indicated that both Cd and NP caused oxidative damage to H. dubia. Under the stress, the antioxidant defense systems were activated, the activity of superoxide dismutase (SOD) was significantly decreased. The activity of catalase (CAT) reacted negatively under stress alone, but increased significantly under combined stress. The activity of peroxidase (POD) increased, which was used to alleviate the damage caused by toxics stress. The joint toxicity evaluation showed that the joint toxicity of Cd and NP to H. dubia was antagonistic when the concentrations of Cd + NP were 0.01 + 0.1 mg/L and 0.01 + 1 mg/L. At 0.5 + 0.1 mg/L and 0.5 + 1 mg/L, Cd and NP had a strong synergistic effect on H. dubia.

Study on the Joint Toxicity of BPZ, BPS, BPC and BPF to Zebrafish

Bisphenol Z (BPZ), bisphenol S (BPS), bisphenol C (BPC), and bisphenol F (BPF) had been widely used as alternatives to bisphenol A (BPA), but the toxicity data of these bisphenol analogues were very limited. In this study, the joint toxicity of BPZ, BPS, BPC, and BPF to zebrafish (Danio rerio) was investigated. The median half lethal concentrations (LC50) of BPZ, BPS, BPC, and BPF to zebrafish for 96 h were 6.9 × 105 µM, 3.9 × 107 µM, 7.1 × 105 µM, and1.6 × 106 µM, respectively. The joint toxicity effect of BPF–BPC (7.7 × 105–3.4 × 105µM) and BPZ–BPC (3.4 × 105–3.5 × 105µM) with the same toxic ratio showed a synergistic effect, which may be attributed to enzyme inhibition or induction theory. While the toxicity effect of the other two bisphenol analogue combined groups and multi-joint pairs showed an antagonistic effect due to the competition site, other causes need to be further explored. Meanwhile, the expression levels of the estrogen receptor genes (ERα, ERβ1) and antioxidant enzyme genes (SOD, CAT, GPX) were analyzed using a quantitative real-time polymerase chain reaction in zebrafish exposure to LC50 of BPZ, BPS, BPC, and BPF collected at 24, 48, 72, and 96 h. Relative expression of CAT, GPX, and ERβ1 mRNA declined significantly compared to the blank control, which might be a major cause of oxidant injury of antioxidant systems and the disruption of the endocrine systems in zebrafish.

Current Progress on Marine Microplastics Pollution Research: A Review on Pollution Occurrence, Detection, and Environmental Effects

Recently, microplastics pollution has attracted much attention in the environmental field, as researchers have found traces of microplastics in both marine and terrestrial ecological environments. Here, we reviewed and discussed the current progress on microplastics pollution in the marine environment from three main aspects including their identification and qualification methods, source and distribution, and fate and toxicity in a marine ecosystem. Microplastics in the marine environment originate from a variety of sources and distribute broadly all around the world, but their quantitative information is still lacking. Up to now, there have been no adequate and standard methods to identify and quantify the various types of microplastics, which need to be developed and unified. The fate of microplastics in the environment is particularly important as they may be transferred or accumulated in the biological chain. Meanwhile, microplastics may have a high adsorption capacity to pollutants, which is the basic research to further study their fate and joint toxicity in the environment. Therefore, all the findings are expected to fill the knowledge gaps in microplastics pollution and promote the development of relative regulations.