Implications of seasonal priming and reproductive activity on the interpretation of Comet assay data derived from the clam, Tapes semidecussatus Reeves 1864, exposed to contaminated sediments

We explore the use of the clam Tapes semidecussatus Reeves 1864 as an indicator for the presence of potentially genotoxic substances in estuarine sediments. The limitations associated with the interpretation of Comet assay data (expressed as % DNA in tail) in terms of clam reproductive state, size (age) and thermal exposure history following laboratory acclimation are discussed. Hatchery-reared clams, subjected to ambient temperature fluctuations during growth, were exposed in vivo under laboratory conditions for three weeks to sediment samples collected from a polluted site and a "clean" reference site. The DNA damage observed in haemocytes, gill and digestive gland cells was significantly higher in animals exposed to contaminated sediment compared to those exposed to sediment from the reference site. The extent of DNA damage recorded was not correlated with size (age). Spawning was not observed during the experiment. Nevertheless, clams with well-developed gonads showed a statistically higher degree of DNA damage in gill and digestive gland cells- but not haemocytes, demonstrating an increased sensitivity to potential genotoxic compounds, possibly caused by impaired DNA repair capacity due to reproductive activity. Furthermore, the degree of DNA damage in clams exposed to contaminated sediments was higher in autumn and winter compared to spring and summer, suggesting an effect of seasonal priming.     

Relative potency of PAHs and heterocycles as aryl hydrocarbon receptor agonists in fish

The relative potency of polycyclic aromatic compounds as aryl hydrocarbon receptor (AhR) agonists in fish was determined using data on CYP1A induction or AhR binding for 74 polycyclic aromatic hydrocarbons (PAHs) and heterocycles in teleost, avian, or mammalian systems from 18 published papers. Each PAH was assigned a fish potency factor relative to the potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin as an AhR agonist. Two and three ring unsubstituted PAHs were generally inactive in fish, avian, and mammalian systems. Benzo[k]fluoranthene and indeno[1,2,3-cd]pyrene were consistently the most potent PAHs, with fish potency factors of 0.001-0.002. Common structural features associated with higher potency PAHs included 4-6 rings containing fluoranthene or phenanthrene structures with an exposed bay region. These results show that PAHs can have similar potency as many dioxin-like PCBs, and AhR mediated toxicity should be considered in assessing the risks of PAHs in fish.     

Arctic versus temperate comparison of risk assessment metrics for 2-methyl-naphthalene

Reliable risk assessment approaches for Arctic environments are requested to manage potential impacts associated with increased activities in Arctic regions. We performed toxicity tests on Arctic and temperate species exposed to the narcotic acting oil component, 2-methyl naphthalene. The experimental results were used to quantify concentration causing lethality to 50% of exposed individuals and no-effect concentration (individual level). For estimates at community level, the hazardous concentrations affecting 5% and 50% of the species were calculated from sensitivity distribution curves. These survival metrics were then used to elucidate whether temperate toxicity data used in risk assessment are sufficiently representative for the Arctic. Taking data uncertainty into consideration, we found no regional difference in tolerances to 2-methyl naphthalene either at the species level or at the community level. Hence these data support a conclusion that values of survival metrics for temperate regions are transferrable to the Arctic for the chemical 2-methyl naphthalene, as long as extrapolation techniques are properly applied and uncertainties are taken into consideration.     

Can starvation influence cellular and biochemical parameters in the crab Carcinus aestuarii?

Crustacea experience periods of starvation during moulting or when limited food availability occurs. The effects of starvation on Crustacea physiological responses have been demonstrated, whereas the effects of starvation on Crustacea immune parameters remain to be more fully studied. In the present study the effects of starvation on immune parameters and antioxidant enzyme activities of the crab Carcinus aestuarii were evaluated for the first time. Treated crabs were starved for 7 days, whereas control crabs were fed daily with mussels. Total haemocyte count (THC), haemocyte diameter and volume, haemocyte proliferation, cell-free haemolymph (CFH) glucose and total protein levels, and phenoloxidase (PO) activity in both haemocyte lysate (HL) and CFH were measured in crabs. In addition, superoxide dismutase (SOD) and catalase (CAT) activities were evaluated in both gills and digestive gland from crabs, in order to evaluate whether starvation induced oxidative stress in C. aestuarii. THC increased significantly in starved crabs, with respect to controls, whereas no significant variations were observed in haemocyte diameter, volume and proliferation. In CFH of starved animals glucose concentration significantly increased, whereas total protein concentration significantly reduced. A significantly higher PO activity was recorded in HL from starved crabs, than in control crabs. Conversely, PO activity did not vary significantly in CFH. Starvation did not cause significant alterations in antioxidant enzyme activities in both gills and digestive gland. Results obtained demonstrated that starvation influenced crab immune parameters, but did not induce oxidative stress. Results also indicated that C. aestuarii can modulate its cellular and biochemical parameters in order to cope with starvation.     

Exposure of the clam Tapes philippinarum to 4-nonylphenol: changes in anti-oxidant enzyme activities and re-burrowing capability

The effects of 4-nonylphenol on anti-oxidant enzyme (superoxide dismutase and catalase) activity in both gills and digestive gland and re-burrowing capability of the clam Tapes philippinarum were investigated after 7 days' exposure to various sublethal concentrations of nonylphenol (NP). NP caused a significant decrease in superoxide dismutase activity in both tissues from the lowest concentration tested, whereas no significant alteration with respect to controls was observed in catalase activity. NP effects on re-burrowing of clams were evaluated in two experiments. In the first, clams exposed to the highest NP concentrations showed a marked delay in re-burrowing 48 h after the end of exposure. Modifications in normal burrowing behaviour were also observed, suggesting that NP acts via narcosis and/or neurotoxic mechanisms. In the second experiment, the elapsed time for 50% of the exposed clams to re-burrow into the sediment (RT(50)) was also calculated in a 24-h re-burrowing response test. At the highest NP concentrations, it was not possible to estimate RT(50) values, as the percentage of clams showing complete burial was less than 50%. The present study demonstrates that NP causes oxidative stress by inhibiting superoxide dismutase activity and greatly affects the re-burrowing capability of T. philippinarum, even at environmentally realistic concentrations.