Contamination by PAHs, PCBs, PCPs and heavy metals in the mecoácfin lake estuarine water and sediments after oil spilling

INTENTION, GOAL, SCOPE, BACKGROUND: Environmental pollution caused by oil spills is a major ecological problem. Oil contamination in the environment is primarily evaluated by measuring the chemical concentrations of hydrocarbons. The results of chemical analyses are important for estimating water and sediment quality in the risk assessment to the flora and fauna of oil-contaminated sites. In the world there are lake ecosystems under permanent chemical stress due to urbanization and the oil industry. Studies, however, have been generally limited to petroleum compounds and have not considered other pollutants of the site like PCBs, polychlorinated pesticides and heavy metals. OBJECTIVE: Water and sediment from stations in the Mecoacán Lake in the Mexican State of Tabasco were analyzed for polycy-clic aromatic compounds (PAHs), aliphatic hydrocarbons (AHs), polychlorinated biphenyls (PCBs), polychlorinated pesticides (PCPs) and heavy metals. The objective of this study was to examine the contaminant levels of the samples collected in February 1993 and 1996 after oil spills at the Mecoacán petroleum region. The goals of this study were to reveal the effect of the spills on the distribution of the hydrocarbons and assess the toxi-cological significance of the levels found. In addition, our aim was to examine the distribution of the PAHs in sediments from Mecoacán originated from both pyrolytic and petrogenic sources. METHODS: Samples were collected from 19 stations and prepared according to the CARIPOL (Caribbean Pollution) methodology of the United Nations Environmental Programme (1992) of the Great Caribbean Region for hydrocarbons in marine and coastal water, and sediments. The gas-chromatographic and atomic absorption analysis of the samples was performed after sampling. RESULTS AND DISCUSSION: Concentrations of PAHs in water ranged from 0.2 to 0.8 μg/l in 1993 and from 0.3 to 2.8 μg/l in 1996. The concentration of the 16 EPA-PAHs varied from 0.1 to 36 mg/kg dry weight in the lake sediment samples collected in 1996, while those of AHs, PCBs and PCPs ranged from 0.1 to 67 mg/kg, 0.1 to 59 μg/kg and 6 to 370 μg/kg, respectively. The most abundant contaminants in water were benz[a]anthracene and pyrene, in 1993 and 1996, respectively; while in sediments collected in 1996: Pyrene, C₂₄, 2-chlorobiphenyl and endrin predominated. Heavy metals (Cu, Pb and Zn) were found at low concentrations. Benzo[a]pyrene was detected in some sediment samples in varying amounts (0.2 to 0.3 mg/kg). CONCLUSIONS: The maximum total PAH concentration in sediments was found at sites near the oil fields and the AH concentration near the urban zone. The mayor pollutants in sediments were PAHs and AHs, and taking into regard the detected PAHs near the oil fields, the source was the oil spilling. The mean total PAH value in Mecoacan sediments of 6.4 mg/kg did not exceed the median range effects value (ERM) for total PAHs of 44.8 mg/kg. The measured organochlorine compounds and heavy metals were present in amounts much inferior to the ERM values. This study confirms that contaminants concentration in sediments did not exceed the environmental quality guideline for the 50% probability and no adverse effect can be expected. RECOMMENDATION AND OUTLOOK: Analysis revealed no indication of a contribution of PAHs, PCBs, PCPs and heavy metals to acute sediment toxicity. The results of this study demonstrate the importance of continuous monitoring of ecosystems exposed to pollution to make pre-spill data available in order to evaluate the real consequence of the spilling and its effect on flora and fauna.