Evaluation of genotoxic responses of Chaetoceros tenuissimus and Skeletonema costatum to water accommodated fraction of petroleum hydrocarbons as biomarker of exposure.

Genotoxic responses towards chronic exposure of Chaetoceros tenuissimus and Skeletonema costatum to water accommodated fraction of petroleum hydrocarbons (WAF-P) were evaluated as biomarkers of petroleum hydrocarbons pollution. The DNA damage caused by water accommodated fraction of petroleum hydrocarbons was assessed in terms of the DNA integrity measured by alkaline unwinding assay. The comparative study of the growth pattern of C. tenuissimus with respect to DNA integrity and the DNA strand breaks in different concentrations of WAF-P showed sufficient tolerance. However, its toxicity increased proportionately with exposure to elevated levels of WAF-P. Although DNA damage in S. costatum was similar to C. tenuissimus, its tolerance level to WAF-P was at least 5 times lower than that of C. tenuissimus indicating its high sensitivity to petroleum hydrocarbons. Active growth was exhibited by C. tenuissimus between 10 and 20% WAF-P (ranging from 0.59 to 1.18mg/L petroleum hydrocarbons) which can be related to the polluted regions only, suggesting the tolerant nature of this organism. Considering the degree of sensitivity to petroleum products and good growth under laboratory conditions, these two diatoms could be recommended as model species for evaluating ecogenotoxic effects of wide range of petroleum hydrocarbon pollutants using alkaline unwinding assays.

Application of oxidative stress indices in natural populations of Perna viridis as biomarker of environmental pollution.

Oxidative stress indices were measured in gills and digestive glands of Perna viridis collected from three coastal locations in Goa i.e., Bambolim, Marmugao Harbour and Malim. In addition to lipid peroxidation, the activities of antioxidant enzymes such as superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione S-transferase and two non-enzymatic antioxidants (ascorbic acid and reduced glutathione) were investigated in order to understand their variation with respect to pollution status of the sampling locations. We observed a significant increase in lipid peroxidation and antioxidant enzymes of both the tissues at Mormugao Harbour and Malim, suggesting that the animals at these two locations are at higher level of oxidative stress as compared to those at Bambolim. Conversely, low levels of non-enzymatic antioxidants such as ascorbic acid and reduced glutathione, observed at Mormugao Harbour and Malim indicate that the animals may use these compounds to counteract stress in the tissues. This study shows that changes in lipid peroxidation, superoxide dismutase, catalase, glutathione reductase, glutathione S-transferase and reduced glutathione in tissues of P. viridis can be used as molecular biomarkers in environmental monitoring programs.

Modulation of antioxidant defences in digestive gland of Perna viridis (L.), on mercury exposures.

Sub-lethal effects of mercury exposure (110th of LC(50), i.e. 0.045 mg l(-1)) for 5, 10 and 15 d was investigated on oxidative stress parameters and antioxidant defences in digestive gland of Perna viridis. In addition to this an in vitro effect of mercury single and supplemented with reduced glutathione on lipid peroxidation was studied. Increased lipid peroxidation (during first 10 days and also during in vitro exposures), protein carbonyl and hydrogen peroxides (from 5th till last day of exposure) indicate the resultant oxidative stress in the mercury exposed specimen. DNA damage (F-value) response although less distinct on 5th and 15th d, its low values on 10th d and significant correlation with hydrogen peroxide suggests the toxic role of free radicals towards DNA integrity. Superoxide dismutase, which remains low initially (5th d) and increases later suggests its immediate response against superoxide radical. Higher activities of catalase, glutathione peroxidase and glutathione reductase on 15th d and glutathione-S-tranferase from 10th d onwards suggests the adaptive behaviour of the tissue against oxyradicals. Increasing levels of non-enzymatic antioxidant molecules, such as reduced glutathione and ascorbic acid indicated its involvement in counteracting oxidative damage. Further role of reduced glutathione in reducing Hg toxicity is evident in in vitro experiments where lipid peroxidation remains low in mercury concentrations supplemented with reduced glutathione. The elevated levels of metallothionein from 5th to 10th d suggest involvement of this protein in detoxification of reactive oxygen species and toxic metal. The above results suggest that both enzymatic and non-enzymatic antioxidants play an important role in protecting cell against Hg toxicity, which can be used as a biomarker of metal contamination in aquatic environment.

Biochemical markers of oxidative stress in Perna viridis exposed to mercury and temperature.

Oxidative damage and antioxidant properties have been studied in Perna viridis subjected to short-term exposure to Hg along with temperature (72h) and long-term temperature exposures (14 days) as pollution biomarkers. The elevated thiobarbituric acid reactive substances (TBA-RS) levels observed in gills and digestive gland under exposure to Hg, individually and combined with temperature, as also long-term temperature stress have been assigned to the oxidative damage resulting in lipid peroxidation (LPX). Increased activities of antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-S-transferase (GST) both in gills and digestive glands under long-term exposures to temperatures are more prominent to heat rather than cold stress suggesting activation of physiological mechanism to scavenge the ROS produced during heat stress. Also decreased values of reduced glutathione (GSH) on long exposures to temperature stress indicate utilisation of this antioxidant, either to scavenge oxiradicals or act in combination with other enzymes, was more than its production capacity under heat stress. The results suggest that temperature variation does alter the active oxygen metabolism by modulating antioxidant enzyme activities, which can be used as biomarker to detect sublethal effects of pollution.

Dissolved oxygen--a target indicator in determining use of the Gulf of Kachchh waters.

Spatial and temporal variations of Dissolved Oxygen (DO) and Biochemical Oxygen Demand (BOD) in the Gulf of Kachchh (GoK), India are assessed based on data collected since 1976. DO concentrations in the interior GoK vary within a narrow range (6.05-6.86 mg l(-1)), whereas near-shore waters show wider variations (3.5-7.8 mg l(-1)). The DO concentration levels in the Gulf waters are close to saturation, varying from 75.4% to 108.6%, which is much higher than the 60% saturation level set for the SW-1 waters. BOD-DO simulation shows that when effluents containing a BOD concentration of 50.0 mg l(-1) are introduced at three select locations, DO reduces from 5.1 mg l(-1) to 3.1, 5.0 and 3.8 mg l(-1), respectively, indicating a strong sensitivity to effluent load. Based on the DO analysis, BOD assimilation capacity of coastal waters around the Marine National Park (MNP) and Marine Sanctuary (MS) in the Gulf is determined. DO available for utilization for various categories of water use is illustrated, keeping in mind the ecology of MNP and MS areas. The significance of DO as a target indicator to zone the Gulf for different water use, is highlighted in this study.

Marine environmental pollution stress detection through direct viable counts of bacteria.

Direct viable counts (DVC) of bacteria were quantified from polluted and relatively less/non-polluted coastal locations during different seasons to assess whether they can be routinely monitored for an understanding of environmental stress(es) that may impede the full functioning of bacterial communities in situ. Most notably, DVC were quite low during pre-monsoon (March-May) in pollution-affected locations when compared to relatively less/non-polluted ones. In contrast, their abundance was significantly higher (up to or > 10%) suggesting a substantially higher microbial activity (thus, a larger turnover of organic matter) during monsoon (June-September) and post-monsoon (October-February) even in pollution-affected locations. The ease of reliably measuring DVC was useful in realising decreased metabolic functioning of bacteria during pre-monsoon, a season where dispersion of land discharges/effluents is much lower. From laboratory and field analyses of this study it is ascertained that DVC are direct indices of potential bacterial metabolic activity, reliable for sensing metabolic stress experienced by bacterial communities in situ and can be useful for evaluating risks in marine environment through human (industrial) activities.