One of the major environmental impacts of oil exploration in the Ecuadorian Amazon region is the contamination of the aquatic environment. In addition to occasional major oil spills, there are several minor sources. This study investigates aquatic toxicity due to seepage from production pits and oiled road run-off. Water and sediment samples were collected and acute toxicity was determined in Daphnia magna and Hyalella azteca bioassays. Because exposure to ultra-violet radiation may enhance the toxicity of several polycyclic aromatic hydrocarbons in crude oil, toxicity was studied before and after exposure to natural sunlight in the field using a microbiotest or solar-simulating ultra-violet light in the laboratory using cultured organisms.

Total petroleum hydrocarbon concentrations of analyzed sediments ranged from 4.9 to 6980 mg kg−1 dry weight (dw). Immobility and lethality ranged from 0 to 100% in Daphnia magna and from 0 to 40% in Hyalella azteca. The micro-biotest results were generally confirmed by the tests on cultured Daphnia. A river exposed to oiled road run-off and a pond used for drinking water, 100-m from a production pit, had the highest total petroleum hydrocarbon concentrations. These samples were toxic compared to reference sites. The response increased upon light exposure, suggesting polycyclic aromatic hydrocarbon availability. Minor water phototoxicity was also observed in the drinking water pond (having ten times the total petroleum hydrocarbon concentration nationally allowed in drinking water). Thus, the seepage from unlined production pits and the practice to use oil for dust control on roads in the area pose environmental and human health hazards.

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