DNA damage and biochemical responses in estuarine bivalve Donax incarnatus (Gmelin, 1791) exposed to sub-lethal concentrations of an organophosphate pesticide monocrotophos.

Monocrotophos (MCP) is a highly toxic and broad-spectrum pesticide extensively used for agricultural and household purposes. The present study was aimed to evaluate the genotoxicity and alterations in the biochemical and physiological conditions induced by monocrotophos in a non-target organism, an estuarine bivalve, Donax incarnatus. The bivalves were exposed to three sub-lethal concentrations (6.8, 13.7, and 27.45 ppm) of MCP for a period of 72 h. DNA damage was assessed using the comet assay. Oxidative stress was analyzed using catalase, glutathione peroxidase, and superoxide dismutase. Neurotoxicity was evaluated using the acetylcholinesterase assay (AChE) and the physiological condition was assessed using the condition index (CI). A significant concentration-dependent increase of DNA damage was observed as well as a decline in the activities of the antioxidant enzymes. However, a decrease in DNA damage was observed with advancing time. A significant decrease of AChE activity and CI was observed in the bivalves exposed to MCP. Positive correlations were also observed between DNA damage and the antioxidant enzymes whereas negative correlations were observed between AChE and the antioxidant enzymes indicating MCP toxicity mediated by oxidative stress.

Native hypersaline sulphate reducing bacteria contributes to iron nanoparticle formation in saltpan sediment: A concern for aquaculture.

A hypersaline dissimilatory sulphate reducing bacterium, strain LS4, isolated from the sediments of Ribander saltpan, Goa, India was found to produce (Fe2O3) maghemite nanoparticles. The presence of maghemite nanoparticles was also detected in the same sediment. Strain LS4 was isolated anaerobically on modified Hatchikian's media at 300 psu, growing optimally at 30 °C, 150 psu salinity and pH 7.8. Based on biochemical characteristics and 16S rRNA sequence analysis, the strain LS4 belongs to genus Desulfovibrio. This isolate synthesized iron oxide nanoparticles in vitro when challenged with FeCl3 & FeSO4 in the growth medium. The biological nanoparticles were characterized to be Fe2O3 nanoparticle of 19 nm size by X-ray diffraction, transmission electron microscopy, fourier transform infrared spectroscopy, scanning electron microscopy and energy-dispersive x-ray spectroscopy. Maghemite nanoparticles (5.63 mg g-1) were isolated from the saltpan sediment by magnetic separation which showed similar characteristic features to the Fe2O3 nanoparticle produced by strain LS4 with an average size of 18 nm. Traditionally Goan saltpans were used for aquaculture during the non-salt making season, thus effects of these nanoparticles on Zebra fish embryo development were checked, which resulted in developmental abnormalities and DNA damage in a dose dependent manner. With the increasing nanoparticle concentration (0.1 mg.L-1 to100 mg.L-1), the mortality rate increased with a decrease in the hatching rate (93.05 ± 2.4 to 25 ± 4.16%) and heart rate (150-120 beats per minute). The nanoparticle exposed embryos developed malformed larvae with a characteristic of pericardial edema, curved body, curved notochord, curved tail and curved tail tip. These results suggest that strain LS4 might be playing a role as a contributor in the formation of iron oxide nanoparticle in the Ribander saltpan sediment, however; its high concentration will have a negative impact on aquaculture in these saltpans.

Effects of gamma radiation on the early developmental stages of Zebrafish (Danio rerio).

The zebrafish is gaining importance as a popular vertebrate model organism and is widely employed in ecotoxicological studies, especially for the biomonitoring of pollution in water bodies. There is limited data on the genetic mechanisms governing the adverse health effects in regards to an early developmental exposure to gamma radiation. In the present study zebrafish (Danio rerio) embryos were exposed to 1, 2.5, 5, 7.5 and 10Gy of gamma radiation at 3h post fertilization (hpf). Different developmental toxicity endpoints were investigated. Further, expression of genes associated with the development and DNA damage i.e. (sox2 sox19a and p53) were evaluated using Quantitative PCR (qPCR). The significant changes in the expression of sox2 sox19a and p53 genes were observed. This data was supported the developmental defects observed in the zebrafish embryo exposed to gamma radiation such as i.e. increased DNA damage, decreased hatching rate, increase in median hatching time, decreased body length, increased mortality rate, increased morphological deformities. Further, study shows that the potential ecotoxicological threat of gamma radiation on the early developmental stages of zebrafish. Further, it revealed that the above parameters can be used as predictive biomarkers of gamma radiation exposure.

Bioaccumulation of trace metals and total petroleum and genotoxicity responses in an edible fish population as indicators of marine pollution.

The present study reports the genetic damage and the concentrations of trace metals and total petroleum hydrocarbons prevailing in natural populations of an edible fish, Arius arius in different seasons along the coast of Goa, India as an indicator of the pollution status of coastal water. Fish were collected from a suspected polluted site and a reference site in the pre-monsoon, monsoon and post-monsoon seasons. Physico-chemical parameters as well as the concentrations of total petroleum hydrocarbons (TPH) and trace metals in the water and sediment as well as the tissues of fish collected from these sites were recorded. The genotoxicity status of the fish was assessed employing the micronucleus test and comet assay. A positive correlation (p<0.001) was observed between the tail DNA and micronuclei in all the fish collected. Multiple regression analysis revealed that tissue and environmental pollutant concentrations and genotoxicity were positively associated and higher in the tissues of the fish collected from the polluted site. Pollution indicators and genotoxicity tests, combined with other physiological or biochemical parameters represent an essential integrated approach for efficient monitoring of aquatic ecosystems in Goa.

Evaluation of γ-radiation-induced DNA damage in two species of bivalves and their relative sensitivity using comet assay.

Ionizing radiation is known to induce genetic damage in diverse groups of organisms. Under accidental situations, large quantities of radioactive elements get released into the environment and radiation emitted from these radionuclides may adversely affect both the man and the non-human biota. The present study is aimed (a) to know the genotoxic effect of gamma radiation on aquatic fauna employing two species of selected bivalves, (b) to evaluate the possible use of 'Comet assay' for detecting genetic damage in haemocytes of bivalves as a biomarker for environmental biomonitoring and also (c) to compare the relative sensitivity of two species of bivalves viz. Paphia malabarica and Meretrix casta to gamma radiation. The comet assays was optimized and validated using different concentrations (18, 32 and 56 mg/L) of ethyl methanesulfonate (EMS), a direct-acting reference genotoxic agent, to which the bivalves were exposed for various times (24, 48 and 72 h). Bivalves were irradiated (single acute exposure) with 5 different doses (viz. 2, 4, 6, 8 and 10 Gy) of gamma radiation and their genotoxic effects on the haemocytes were studied using the comet assay. Haemolymph was collected from the adductor muscle at 24, 48 and 72 h of both EMS-exposed and irradiated bivalves and comet assay was carried out using standard protocol. A significant increase in DNA damage was observed as indicated by an increase in % tail DNA damage at different concentrations of EMS and all the doses of gamma radiation as compared to controls in both bivalve species. This showed a dose-dependent increase of genetic damage induced in bivalves by EMS as well as gamma radiation. Further, the highest DNA damage was observed at 24h. The damage gradually decreased with time, i.e. was smaller at 48 and 72 h than at 24h post irradiation in both species of bivalves. This may indicate repair of the damaged DNA and/or loss of heavily damaged cells as the post irradiation time advanced. The present study reveals that gamma radiation induces single strand breaks in DNA as measured by alkaline comet assay in bivalves and comet assay serves as a sensitive and rapid method to detect genotoxicity of gamma radiation. This study further indicates that both M. casta and P. malabarica exhibit almost identical sensitivity to gamma radiation as measured by DNA damage.