Toxicity of engineered nanoparticles to marine bivavle molluscs

Abstract

Engineered nanoparticles (ENPs) are increasingly used in manufacturing and consumer products. Their environmental release is a concern given their toxicological effects, which may include interference with cellular electron transport, reactive oxygen species generation, nucleic acid damage, protein oxidation, and cell membrane disruption. This thesis evaluated ENP effects on two tropical filter feeding bivalves (Amiantis umbonella and Asaphis violascens). Nano-silver and nano-titanium dioxide were evaluated over acute (48 hour; concentration 0.05, 0.2, 1, 2 mg/l) and chronic (4-weeks; concentration 0.05 mg/l) exposures. Chronic exposures were also conducted with nano- and bulk-copper and zinc oxides. Bivalve functional activity was measured as particle (microalgae) clearance rate. Simultaneously, a multi-biomarker approach (lipid peroxidation, catalase, glutathione peroxidase, glutathione reductase, glutathione S-transferase, and metallothionein) was used, supported by histopathology, to determine potential metabolic and cellular effects in gill and digestive gland tissues. Responses varied with nanoparticle type, concentration, exposure period, and species. Acute exposure triggered concentration dependent changes as clearance rate reduced with increasing concentration and exposure duration. Gills and digestive glands revealed oxidative injury; however, the respondent antioxidant defence biomarkers varied. Antioxidant enzyme levels were generally lower in the digestive gland with effects more evident at 0.05 mg/l. Bivalves, particularly A. umbonella, ceased filtering at higher concentrations but still registered oxidative injury. Acute exposure at lower concentrations enhanced antioxidant defence; however, cellular damage occurred. Chronically exposed animals were capable of ameliorating some of the damage. Membrane lipid peroxidation by nano-copper and zinc oxide was higher than their bulk states. Histopathology revealed morphological alterations in gills and digestive glands, particularly over longer exposures. Protein expression was examined (SDS-PAGE) in chronically exposed tissues with some changes common to all nanoparticles whereas others were nanoparticle specific. The present study indicates oxidative injury in marine bivalves exposed to ENPs with the gills and digestive gland as target organs.