The joint effect of chlorpyrifos ethyl and fenobucarb on brain acetylcholinesterase activity in climbing perch (Anabas testudineus) fingerlings

Thanh Tam Nguyen, Håkan Berg, Van Cong Nguyen.

Effects of Sequential Applications of Bassa 50EC (Fenobucarb) and Vitashield 40EC (Chlorpyrifos ethyl) on Acetylcholinesterase Activity in Climbing Perch (Anabas testudineus) Cultured in Rice Fields in the Mekong Delta, Vietnam

2016. Thanh Tam Nguyen (et al.). Bulletin of Environmental Contamination and Toxicology 97 (1), 98-104

Article

This study assesses the effects of sequential applications of the insecticides Bassa 50EC (fenobucarb-F) and Vitashield 40EC (chlorpyrifos ethyl-CPF), sprayed at concentrations used by rice farmers in the Mekong Delta, on the brain acetylcholinesterase (AChE) in climbing perch fingerlings. After spraying the pesticides on the rice fields, the water concentrations of both insecticides decreased below the detection levels within three days. The sequential applications caused significant inhibition on the brain AChE activity in the exposed fish. The inhibition by F was quicker, but less prolonged, than for CPF. The inhibition levels caused by the sequential applications were lower than those caused by only CPF and by a mixture of CPF and F. The results indicate that sequential applications of pesticides could have a negative impact on aquatic organisms and fish yields, with implication for the aquatic biodiversity, local people’s livelihood and the aquaculture industry in the Mekong Delta.

The joint toxicity effects of Chlorpyrifos ethyl and Fenobucarb to Climbing perch (Anabas testudineus) from rice fields in the Mekong Delta, Vietnam

2016. Thanh Tam Nguyen, Håkan Berg, Cong Van Nguyen. Environmental science and pollution research international

Article

Organophosphates (e.g. chlorpyrifos ethyl) and carbamates (e.g. fenobucarb), are commonly used to control a wide range of pests in rice fields of the Mekong Delta in Vietnam. This study assesses the combined effect of chlorpyrifos ethyl (CPF) and fenobucarb (F) on the brain acetylcholinesterase (AChE) activity in climbing perch fingerlings from rice fields in the Mekong Delta. It also investigates if Pyridine-2-aldoxime methiodide (2-PAM) can be used to re-activate cholinesterase that has been blocked by CPF and F. Three days after spraying, the water concentrations of both insecticides decreased quickly below the detection levels. However the brain AChE activity in fish was inhibited for more than seven days. The results indicate a quicker but less prolonged inhibition of the brain AChE activity by the mixture than by only CPF. The inhibition levels were above 70% only during the first 48 hours, which could explain why all fish survived. 2-PAM resulted in a significant re-activation of the cholinesterase blocked by a combination of CPF and F, and it is proposed that the re-activation by 2-PAM could provide a way to assess the AChE inhibition level in organisms, when no unexposed individuals are available as controls. The results indicate that current use of CPF and F in rice farming in the Mekong Delta is likely to cause negative effects on non-target organisms. Many of these effects may be sub-lethal, and there is a need to develop relevant bio-markers, that are relevant, cheap and easy to apply under tropical conditions in developing countries.

Effect of Chlorpyrifos Ethyl on Acetylcholinesterase Activityin Climbing Perch (Anabas testudineus, Bloch, 1972)

2015. Thanh Tam Nguyen (et al.). Archives of Environmental Contamination and Toxicology 69 (4), 515-524

Article

The high use of pesticides in intensive rice farming in the Mekong Delta constitutes a potential hazard to the environment and to people's health. Chlorpyrifos ethyl (CPF) is a commonly used organophosphate (OP) insecticide, but information about its potential negative impacts on the aquatic environment in the Mekong Delta is scarce. Both acute and subacute toxicity tests were performed in a static nonrenewable system to investigate the effects of CPF on brain acetylcholinesterase (AChE) activity in native climbing perch fingerlings (Anabas testudineus, Bloch, 1972). Environmental parameters, such as dissolved oxygen, water temperature, and pH, were similar to field conditions in the Mekong Delta. In a 96-h lethal concentration (LC50) test, fingerlings of climbing perch were randomly exposed to five levels of CPF ranging from 0.8 to 4.5 ppm. Five sublethal levels of CPF (1, 5, 10, 15, and 20 % of the 96-h LC50 value) were tested to assess the sensitivity and recovery of the brain AChE activity in climbing perch fingerlings exposed to CPF. The results showed that CPF were moderately toxic to climbing perch with a 96-h median LC50 of 1.73 ppm. CPF also caused long-term AChE inhibition with 70 % inhibition remaining after 96 h for the four highest test concentrations. The recovery of brain AChE activity in fish placed in CPF-free water was very slow, and after 7 days the brain AChE activity was still significant lower in fish from the four highest concentrations compared with the control. The results from this study indicate that OP insecticides, such as CPF, can have long-lasting sublethal effects on aquatic species in the Mekong Delta.

Effects of chlorpyrifos ethyl on acetylcholinesterase activity in climbing perch cultured in rice fields in the Mekong Delta, Vietnam

2015. Thanh Tam Nguyen (et al.). Ecotoxicology and Environmental Safety 117, 34-40

Article

Climbing perch is commonly harvested in rice fields and associated wetlands in the Mekong Delta. Despite its importance in providing food and income to local households, there is little information how this fish species is affected by the high use of pesticides in rice farming. Organophosphate insecticides, such as chlorpyrifos ethyl, which are highly toxic to aquatic organisms, are commonly used in the Mekong Delta. This study shows that the brain acetylcholinesterase (AChE) activity in climbing perch fingerlings cultured in rice fields, was significantly inhibited by a single application of chlorpyrifos ethyl, at doses commonly applied by rice farmers (032-0.64 kg/ha). The water concentration of chlorpyrifos ethyl decreased below the detection level within 3 days, but the inhibition of brain AChE activity remained for more than 12 days. In addition, the chlorpyrifos ethyl treatments had a significant impact on the survival and growth rates of climbing perch fingerlings, which were proportional to the exposure levels. The results indicate that the high use of pesticides among rice farmers in the Mekong Delta could have a negative impact on aquatic organisms and fish yields, with implications for the aquatic biodiversity, local people's livelihoods and the aquaculture industry in the Mekong Delta.

Use of Wastewater from Striped Catfish (Pangasianodon hypophthalmus) Pond Culture for Integrated Rice-Fish-Vegetable Farming Systems in the Mekong Delta, Vietnam

2015. Chau Thi Da (et al.). Agroecology and Sustainable Food Systems 39 (5), 580-597

Article

This article investigates the feasibility of reusing wastewater from striped catfish (Pangasianodon hypophthalmus) pond culture as nutrient input for integrated rice-Nile tilapia-green bean farming systems, and to what extent this could contribute to decreasing the environmental impacts on water quality from the striped catfish industry in the Mekong Delta. Four treatments in triplicates were used to investigate the growth of rice and green bean varieties under different combinations of inorganic fertilizer and water from the river and a striped catfish pond culture. The Nile tilapia (Oreochromis niloticus) was cultured at low density without feeding in a canal adjacent to the rice field. Rice yields ranged from 3,514 to 4,023 kg ha(-1) with no significant differences between treatments (p > 0.05). The yield of green bean ranged from 2,671 to 3,282 kg ha(-1) (p < 0.05), with the highest yields for beans only receiving water from the striped catfish pond. The water quality concentrations decreased significantly when passing through the rice plots for almost all treatments (p < 0.05). Total phosphorus and nitrogen levels in the outflowing water were reduced by almost 50% compared to the inflowing water from the striped catfish pond. Overall, the results indicated that an integrated system generates both economic and environmental benefits as compared to monocultures.

Wetland ecosystem service values and shrimp aquaculture relationships in Can Gio, Vietnam

2014. S. McDonough (et al.). Ecological Indicators 46, 201-213

Article

Wetland valuation methods often apply monetary driven approaches that may undermine intrinsic ecosystem values. Utilizing a stated preference method, the study identified and mapped local stakeholder ecosystem service values between subsistence wetland and shrimp farmer groups in Can Gio, Vietnam. Through focus group choice experiments, ecosystem services correlating to unique price increments and cost/benefit tradeoffs between hypothetical intensive aquaculture developments and mangrove conservation scenarios were investigated. Selection outcomes exhibited strong values for ecosystem services maintained at the hypothetical natural state (core area pre-intervention 45%, post-intervention 55%; buffer zone pre-intervention 65%, post-intervention 73%). Few respondents selected the hypothetical intensive aquaculture development scenario (core area pre-intervention 18%, post-intervention 9%; buffer zone pre-intervention 12%, post-intervention 5%), and instead, most respondents avoided the costs and benefits of intensive aquaculture development in preference for maintaining natural ecosystem services. Group deliberations drew out a higher sense of altruism and responsiveness to intrinsic wetland values that superseded the potential economic gains of aquaculture developments, whereby certain ecosystem services were deemed economically unassociable and irreplaceable for both study groups. The qualitative results expose the difficulties in monetarily measuring ecosystem services, highlighting the need to incorporate approaches that integrate the intrinsic values attached to ecosystem services.

Effects of Hydraulic Retention Time on Organic and Nitrogen Removal in a Sponge-Membrane Bioreactor

2013. Bui Xuan Thanh (et al.). Environmental Engineering Science 30 (4), 194-199

Article

This is the first study on application of a sponge-membrane bioreactor (sponge MBR) for recirculation of aquaculture wastewater in the Mekong delta, Vietnam. Performance of a sponge MBR with a moving-cube sponge medium (20% v/v) was evaluated at different hydraulic retention times (HRTs) for the specific example of catfish pond wastewater. The sponge MBR was operated at HRT values of 8, 4, and 2 h, which correspond to membrane fluxes of 5, 10, and 20 L/m(2) per hour, respectively. The average chemical oxygen demand (COD) removal efficiencies were maintained at 93%, 94%, and 87% at an HRT of 8, 4, and 2 h, respectively, while the average total nitrogen (TN) removal efficiencies were 84%, 70%, and 57%. The COD and TN removal efficiencies decreased with a decrease in HRT (increase in membrane flux). Permeate concentrations of COD and TN were as low as 6.3 and 2.7 mg/L at the operated HRTs, respectively. Compared to the conventional MBR, the sponge MBR had twice the TN removal capacity at the same HRT due to simultaneous nitrification-denitrification. In addition, results implicated that the fouling rate (dTMP/dt) increased in an inverse proportion with HRT (h) according to the power equation (fouling rate = 4.2474 HRT-2.225). Free movement of sponges in the reactor improved fouling due to sweeping of the cake layer on the membrane surface. Results reveal that the sponge MBR was effective in terms of simultaneous organic and nitrogen removal, fouling control, and water recirculation.

Integrated Rice-Fish Farming

2012. Håkan Berg, Charlotte Berg, Thanh Tam Nguyen. Journal of Sustainable Agriculture 36 (8), 859-872

Article

A comparison of agricultural practices, with a specific focus on pesticide use, between rice and rice-fish farmers in the Can Tho' and Tien Giang provinces of the Mekong Delta in 2007, shows that integrated rice-fish farming can provide a competitive alternative to intensive rice mono-cropping, if the farmer restricts the use of pesticides and takes full advantage of the ecosystem services provided by the rice-field ecosystem. In Can Tho', rice-fish farmers had significantly higher income (43.6 million dong ha(-1) year(-1)) than other farmer groups, while this was not seen among rice-fish famers in Tien Giang (32.4 million dong ha(-1) year(-1)), which partly could be due to a high use of insecticides (0.9 kg active ingredient ha(-1) crop(-1)) and comparatively low fish yield among these farmers. The study emphasizes the need to rethink current agricultural systems and to provide opportunities for more diverse systems that maintain and enhance a range of ecosystem services and protect human health. Future production systems should not be optimized to only provide a single ecosystem service, such as rice, but designed to deliver a variety of interlinked ecosystem service such as rice, fish, pest control, and nutrient recycling.

Use of pesticides and attitude to pest management strategies among rice and rice-fish farmers in the Mekong Delta, Vietnam

2012. Håkan Berg, Thanh Tam Nguyen. International Journal of Pest Management 58 (2), 153-164

Article

This study assesses the use of pesticides and attitude to pest management strategies among rice and rice-fish farmersin Can Tho’ and Tien Giang provinces of the Mekong Delta, Vietnam, in 2007. A comparison is made to a similarstudy in 1999, in order to identify changes in patterns of pesticide use and possible influences of integrated pestmanagement (IPM) programmes and brown planthopper (a major pest) outbreaks. One hundred and twenty farmersused 66 different pesticides, similar to the 64 pesticides recorded as being used in the 1999 survey. Nine of the 10 mostpopular pesticides in 2007 were the same as those found to be popular in 1999. Insecticides are used by 73–95% ofthe farmers, which is the most commonly employed type of pesticide. The number of applications of both herbicidesand fungicides has more than halved since 1999 for all farmers, while insecticide applications has doubled for IPMfarmers (those with prior training in IPM methodology). Similarly, the average dose of active ingredient (a.i.) ofinsecticides per crop has decreased slightly for non-IPM rice farmers, while it has more than doubled among IPMfarmers, resulting in almost the same amount of a.i. per crop for all groups of farmers (insecticides 0.6, fungicides 0.5,and herbicides 0.3 kg a.i. ha71 crop71). Overall, the results indicate a temporal trend for more selective use ofpesticides and an increased awareness among non-IPM farmers of the negative side effects of pesticide use.

Håkan BergAssociate professor, Docent

Research projects

Publications

The joint effect of chlorpyrifos ethyl and fenobucarb on brain acetylcholinesterase activity in climbing perch (Anabas testudineus) fingerlings

Effects of Sequential Applications of Bassa 50EC (Fenobucarb) and Vitashield 40EC (Chlorpyrifos ethyl) on Acetylcholinesterase Activity in Climbing Perch (Anabas testudineus) Cultured in Rice Fields in the Mekong Delta, Vietnam

The joint toxicity effects of Chlorpyrifos ethyl and Fenobucarb to Climbing perch (Anabas testudineus) from rice fields in the Mekong Delta, Vietnam

Effect of Chlorpyrifos Ethyl on Acetylcholinesterase Activityin Climbing Perch (Anabas testudineus, Bloch, 1972)

Effects of chlorpyrifos ethyl on acetylcholinesterase activity in climbing perch cultured in rice fields in the Mekong Delta, Vietnam

Use of Wastewater from Striped Catfish (Pangasianodon hypophthalmus) Pond Culture for Integrated Rice-Fish-Vegetable Farming Systems in the Mekong Delta, Vietnam

Wetland ecosystem service values and shrimp aquaculture relationships in Can Gio, Vietnam

Effects of Hydraulic Retention Time on Organic and Nitrogen Removal in a Sponge-Membrane Bioreactor

Integrated Rice-Fish Farming

Use of pesticides and attitude to pest management strategies among rice and rice-fish farmers in the Mekong Delta, Vietnam