ACTIVITIES

1. Review existing available data from agro-chemical use and effects reported on non-target species in the Mekong River Delta;
2. Assess the exposure of aquatic species using bioassays in the lab, in-situ toxicity tests, and digestive fluid extraction; a technique that measure the bioactivity of sediment-bound chemicals by mimicking the digestion that occurs in the gut of a deposit-feeding aquatic invertebrate in vitro;
3. Propose an Ecological Risk Assessment procedure that can be used by Vietnamese pesticide managers as a tool to characterize the actual risks to non-target species in the Mekong River Delta;
4. Implement research methods in exposure assessment and ERA and generate results to be used to show side-effects of pesticides on the aquatic environment and thus help building sustainable agri- and aquaculture in Vietnam.

PROJECT DESCRIPTION

   In this project we focus on the rapidly developing Mekong River Delta Region. The Mekong Delta Region covers around 40 000 km2, and holds a population of about 20 million people. This is thus a densely populated area with close to 500 people/km2 in comparison to average Viet Nam (236 persons/km2). The Mekong Delta is the most important agricultural area in Viet Nam and more than 50% of total crop for exportation is produced here. Also when it comes to aquaculture this region is of outmost importance with more than 55% of the total national production, and when fisheries is added to that, the total production of seafood for export exceeds 60% of the total for Viet Nam. The quality of the water resources of the region is of course a key feature in these achievements.

   However, the role of the Mekong River Delta Region as a key economic region is now jeopardized by conflicting interest between different stakeholders in the rural development of the region. Intensified agriculture leading to increased pesticide use and subsequently reduced water quality and losses for aquaculture operations. Large-scale aquaculture facilities on the other hand tend to suffer from uncontrolled use of various antibiotics in order to control microbial activity in ponds and dams. The combination of both activities creates pollution related problems for water quality in general, reducing both fisheries yield and local peoples access to clean water, which holds back the economic development and thus poverty alleviation as well as impacting negatively on the human health in the Mekong River Delta region.

   We aim at assessing the fate and effects of pesticide runoff from the rice plantations following their application by collecting samples of water, sediment and biota for pesticide analyses and toxicity testing at different occasions during the dry and the wet season. Runoff and ground water leaching will be favored during rainy conditions. Recent studies have shown that storm water runoff is a major water quality problem in agricultural areas (Foe and Sheipline 1993). Following rainstorms organophosphate insecticides (OPs) were found in surface waters of Californian rivers at concentrations that were acutely toxic to organisms used in standard toxicity tests (Kuivila and Foe 1995; Werner et al. 2000; Werner et al. 2004). As a result from these studies the use of OPs is becoming more restricted and the pesticide use in the developed world is gradually shifting towards replacing the water soluble OPs by a more hydrophobic group of pesticides, the pyrethroids. Pyrethroids will be more likely to stick to soil particles where they are applied and less likely to reach the river with rainfall and groundwater. Many of the pyrethroids are also used in the Mekong River Delta area and they are extremely toxic to some aquatic life, such as benthic invertebrates and fish. While most water monitoring programs mainly analyze pesticides that are dissolved in the water, a large fraction of the pesticides will bind to suspended particles and sediment and will not be detected in water analyses. In this project we will collect water samples but also suspended particles and bed sediment for pesticide analyses and toxicity testing. We will thus get a precise understanding of the fate of the pesticides that are reaching the aquatic environment of the Mekong River Delta. Apart from river transported sediments the Mekong Delta also receives an abundant input of both particulate and dissolved organic matter (POM, DOM), such as humic acids. POM and DOM can affect the partitioning, bioavailability and toxicity of organic contaminants such as hydrophobic organochlorines -e.g. DDT, PCBs and Dioxins from the American war (Carter and Suffet 1982; Eadie et al. 1992; Kukkonen et al. 1991). Collected water samples will be analyzed for POM and DOM. Toxicity tests will also be run in presence and absence of POM and DOM to evaluate their potential impact on ambient pesticide toxicity.

MAIN RESULTS

• Completed the surveys on uses of pesticide in the surroundings of Tra Vinh and Nha Trang
• Completed the toxicity tests of two kinds of pesticide on marine organisms (Later calcarifer, Litopenaeus vannamei, unicellular algae…).

Reporters: Do Minh Thu and Bui Thi Minh Ha