Bioaccumulation of gasoline in brackish green algae and popular clams

Abstract

The green algae (Ulva lactuca and Enteromorpha clathrata) and the clams (Tapes decussates and Venerupis aurea) grow together in Timsah Lake, Suez Canal, Egypt. Our ultimate goal is to validate the bioaccumulation of gasoline in the marine organisms and their behavior after exposure to the pollutant, experimentally. These species were treated with a serial treatment of gasoline (1000, 4000, 16,000 and 64,000μl) in aquaria with brackish sea-water for 72h. The tested green algae and clams were taken for an analysis of total hydrocarbon accumulation daily. The statistical analysis showed significant differences between the four species and also between the duration of exposure. The accumulation of gasoline in U. lactuca and E. clathrata reached their maximum after 48h at 1000 and 4000μl. The highest absorption was registered after 24h only at 16,000 and at 64,000μl. U. lactuca recorded complete mortality in 64,000μl at 72h whereas E. clathrata registered death at 48h and 72h in the same treatment. V. aurea was more sensitive than T. decussates. The accumulation of gasoline reached its maximum in V. aurea after only 24h in the first treatment while it retarded to 48h in T. decussates with a lesser accumulation. However, both clam species accumulated the highest amount of petroleum hydrocarbons during the first hour of exposure at the first treatment. In the third and fourth treatments, clams did not accumulate gasoline but began to dispose it from their tissues till it became less than that in the control. Mortality gradually increased with time in each treatment except the last one (64,000μl) in which 100% death of the specimens was observed. In general, the bioaccumulation of gasoline level was in a descending order as follows: U. lactuca>E. clathrata>V. aurea>T. decussates. Their behavior changed from accumulation to detoxification with time and with the increase in pollutant concentration. Generally, these marine biota are sensitive to hydrocarbons and can be used as biomonitors to contaminants in aquatic environments except T. decussates that we recommend the possibility of using it as a good biomonitor in the sediment rather than in the water column.