Preliminary environmental risk assessment of chemical contamination along the Chaguana river basin (south-west Ecuador)
Valencia Avellán, M.G. (2006). Preliminary environmental risk assessment of chemical contamination along the Chaguana river basin (south-west Ecuador). MSc Thesis. Universiteit Antwerpen/Vrije Universiteit Brussel (ECOMAMA): Brussel. 70 pp.
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| Available in | Author |
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Document type: Dissertation
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| Keywords |
Chemical elements > Metals > Heavy metals
Environmental assessment
Pesticides
Risks
Toxicology > Ecotoxicology
Ecuador [Marine Regions]
Marine/Coastal |
| Abstract |
The Chaguana basin is situated in the South-West of Ecuador. It is dominated by commercial banana cultivation, with intensive use of pesticides, fertilizers and other chemicals. Run-off, underground seepage and aerial fall-outs, all have the potential to cause environmental contamination in the basin. No environmental assessment study has ever been conducted in the area. Therefore, the main objective of this study was to conduct a preliminary Environmental Risk Assessment (ERA) in the area. The study employed the general principles of ERA, which consists of; i) Environmental exposure assessment, which in our case involved determination of the environmental concentrations of suspect toxicants, and ii) Effect assessment to determine the potential toxicity of suspected toxicants. Exposure assessment revealed that among the many organic contaminants screened only DDT derivatives were detectable and the levelswere close to threshold concentrations known to cause toxicity to the aquatic biota. Most heavy metals (Ag, As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and Zn) were also detected and for some (i.e. Pb, Zn) the levels were higher than what you would expect in a pristine area. Agricultural chemicals used in the area may contain traces of heavy metals and unlike most organic pollutants that are biodegradable over time heavy metals tend to accumulate in sediments. Another source of metal contamination appeared to be from natural processes including volcanic fall-outs. When compared with literature toxicity data of individual contaminants, the levels of measured contaminants in this study were below toxic concentrations, though some metals were within an order of magnitude. However, results from toxicity tests using three levels i. e. bacteria, algae and invertebrates bioassays showed clear toxicity. Three main explanations (hypothesis) are suggested. Firstly, levels of some measured contaminants were close to toxic levels, therefore incombination the sum effects of these toxicants may have caused toxicity, secondly, toxicity may also have been caused by any of the many potential toxic ants, which we did include in the screening process, and the third explanation is the role of environmental factors like pH, particle size distribution, organic matter, which may have confounded or exacerbated _toxicity. Overall, the results from both exposure assessment and effect assessment did not seem to reveal a contamination gradient following the river. There are many possible explanations, but essentially it was concluded that whatever level of contamination was present in the basin, it was not too serious. However, there is still need for further ERA due to the presence of so many contaminants in the area and the interactions with receivingenvironment. Future ERA should take into account high natural background levels of heavy metals in predicting environmental concentrations (P EC) of the chemicals in this area. Regarding the toxicity tests used, firstly it is recommended that use of algae growth inhibition assay for whole sediment extracts may not be appropriate since nutrients extracted from sediments were shown to confuse the dose-response relationships. About bacterial gene profiling assay (BGP A), this novice assay has demonstrated to be a useful addition to the traditional battery of toxicity tests used in ERA. The fact that BGP A results can be linked to higher responses such as growth means that the test can be used to detect toxic levels at much lower concentrations, which is better for the protection of the environment. |
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