Nano titanium dioxide alleviates the toxic effects of tris (2-chloropropyl) phosphate on the digestive gland and hemolymph of thick-shell mussel Mytilus coruscus.

In the marine environment, nanoparticles play a role in adsorbing and catalytically degrading organic pollutants, thereby mitigating their toxic effects on aquatic organisms. This study aimed to investigate the impact of nano titanium dioxide (nTiO2) and tris (2-chloropropyl) phosphate (TCPP) on the hemolymph and digestive function of the thick-shell mussel Mytilus coruscus. Mussels were divided into a control group, a group exposed to TCPP alone, a group exposed to a combination of TCPP and 0.5 mg/L nTiO2, and a group exposed to a combination of TCPP and 1 mg/L nTiO2. After 14 days of exposure, oxidative stress responses, including superoxide dismutase (SOD) activity and malondialdehyde (MDA) content, immune defense responses, including acid phosphatase (ACP) and alkaline phosphatase (AKP) activities, and gene expression, including HSP70 expression, were measured in the hemolymph and digestive glands of the mussels. Compared to the control group, mussels solely exposed to 100 µg/L TCPP exhibited a significant reduction in SOD activity in the hemolymph. When TCPP was co-exposed with 0.5 mg/L nTiO2, there were significant increases in MDA content and AKP activity in both the digestive gland and hemolymph compared to the control group. Upon co-exposure of TCPP with 1 mg/L nTiO2, MDA content and AKP activity in the digestive gland significantly decreased, while SOD, ACP, and AKP activity in the hemolymph significantly increased and MDA content significantly decreased, returning to the control group levels. Furthermore, in the combined exposure, HSP70 gene expression significantly decreased as the nTiO2 concentration increased from 0.5 mg/L to 1 mg/L. In summary, TCPP impacted the hemolymph and digestive function of mussels, whereas a concentration of 1 mg/L nTiO2 effectively alleviated the toxic effects of TCPP. This study is crucial for assessing the ecological risks of nanoparticles and emerging organic pollutants in marine environments, and provides new insights into the interaction between nTiO2 and TCPP, as well as the influence of nTiO2 concentration on mitigating TCPP toxicity.

Dietary exposure to nTiO2 reduces byssus performance of mussels under ocean warming.

Nano­titanium dioxide (nTiO2) is a widely used nanomaterial posing potential ecological risk for marine ecosystems that might be enhanced by elevated temperatures such as expected during climate change. nTiO2 may affect benthic filter feeders like mussels through waterborne exposures and via food chain due to the adsorption on/in algae. Mussel byssus are proteinaceous fibers secreted by byssal glands of the mussels for attachment. Byssus production and mechanical properties are sensitive to environmental stressors but the combined effects of warming and nTiO2 on byssus performance of mussels are unclear hampering our understanding of the predation and dislodgement risk of mussels under the multiple stressor scenarios. We explored the effects of a short-term (14-day) single and combined exposures to warming (28 °C) and 100 µg L-1 nTiO2 (including food co-exposure) on the byssus performance of the thick shell mussel Mytilus coruscus. The mechanical strength (measured as the breaking force) of the byssal threads was impaired by warming and nTiO2 (including food co-exposure), but the number and length of the byssal threads were increased. The mRNA expression levels of mussel foot proteins (mfp-3, mfp-5) and pre-collagens (preCOL-D, preCOL-P, preCOL-NG) were up-regulated to varying degrees, with the strongest effects induced by warming. This indicates that the physiological and molecular mechanisms of byssus secretion are plastic. However, downregulation of the mRNA expression of preCOL-D and preCOL-P under the combined warming and nTiO2 exposures indicate the limits of these plasticity mechanisms and suggest that the attachment ability and survival of the mussels may be impaired if the pollution or temperature conditions further deteriorate.

nTiO2 alleviates the toxic effects of TCPP on mussels by adjusting respiratory metabolism and gut microbiota.

As a good carrier of contaminants, nanotitanium dioxide (nTiO2) can absorb organic pollutants, producing toxicological effects on organisms. However, the complex effects of nTiO2 with contaminants on marine mussels are still unclear. In this study, we exposed mussels to tris (2-chloropropyl) phosphate (TCPP) 100 µg/L (T1), 0.5 mg/L nTiO2 + 100 µg/L TCPP (T2), 1.0 mg/L nTiO2 + 100 µg/L TCPP (T3) and control (0 nTiO2 + 0 µg/L TCPP) treatments, and assessed the combined effects of TCPP with nTiO2 on the thick-shelled mussel Mytilus coruscus by detecting the activities of gill pyruvate kinase (PK), hexokinase (HK), lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH), also gill acetylcholine (Ach) and muscle lactic acid (LD) contents and gut microbiota after 14-d exposure. Compared with the control group, PK activity was increased significantly, but SDH, LDH activities and LD content were decreased significantly in T1, with the addition of nTiO2, there were not significantly different in T3. However, Ach content in T3 was significantly higher than the control and T1. Moreover, KEGG of the gut microbiota via 16 s rRNA sequencing showed that most pathways returned to the control level in T3. The results showed that TCPP affected the respiratory metabolism of mussels, changed the community structure of intestinal microflora in mussels, and nTiO2 alleviated the toxicity of TCPP. Our study provides new insights for ecological risk assessment of TCPP in bivalves in the complex aquatic environment and the novel role of nTiO2 in regulating the toxicity of TCPP.