Except for one location, Tanéka-Koko, all areas were contaminated by more thanĢ0 pesticides. Locations along the Ouémé River from upstream to downstream. In this study, organochlorine and organophosphorous pesticide residues were measured in more than 35 sediment samples collected on nine It is 510 km long and its catchment drains 75% of the country. The Ouémé River is one of the most important rivers in the Republic of Bénin. As a result, there is a need to establish a programme for monitoring persistent organic pollutants in Kenya, so that any elevation in concentration above the environmental quality standards can be detected and appropriate actions taken to minimize potential adverse effects to the environment and public health. DDT showed an adverse biological effect to sediment dwelling organisms. The concentration values for PCB, HCB, Heptachlor epoxide, and Chlordane in this study indicate low ecological risk to sediment dwelling organisms. The ecotoxicological impact of sediment pollution by PCBs and OCPs was assessed using sediment quality guidelines specified by the Canadian Council of Ministers of the Environment. The calculated values of DDD+DDE/ DDT showed that the presence of DDT from both the rivers is a result of historical input. Sabaki Bridge in the Sabaki River and Tana 4 in the Tana River recorded high levels of both PCBs and OCPs. The concentration range of PCBs and OCPs were 0.65-9.29 ng/g dw and 0.47-9.84 ng/g dw, respectively. Polychlorinated biphenyls (PCBs) and Organochlorine pesticides (OCPs) in the surface sediments of the Sabaki and Tana estuaries were studied to determine distribution as well as their ecological risk. Lack of any study on pesticides on sludge is largely because domestic wastewater is often not considered as a source of pesticide pollution, thus, studies focus more on river sediments exposed to agrochemicals. In Africa, 9 studies have reported PPCPs in sludge (Agunbiade and Moodley, 2016 Belhaj et al., 2016 Kimosop et al., 2016 Lehutso et al., 2017 Matongo et al., 2015a Oluwatosin et al., 2016 Schoeman et al., 2017) and river sediments (Agunbiade and Moodley, 2016 Kimosop et al., 2016 Matongo et al., 2015a Rimayi et al., 2018a), whereas there are 18 studies (Barakat et al., 2013 Dabrowski et al., 2002 Ezemonye et al., 2015 Gakuba et al., 2018 Hellar-Kihampa et al., 2011, 2013Ibigbami et al., 2015 Kilunga et al., 2017 Kuranchie-Mensah et al., 2012 Lalah et al., 2003 Muendo et al., 2012 Musa et al., 2011a Mwanamoki et al., 2014 Ntow, 2001 Ogbeide et al., 2015 Okoya et al., 2013 Otieno et al., 2013 Twesigye et al., 2011) dealing with pesticides in sediments. Adsorbed compounds may persist in the environment and can be detected long after such compounds are out of use. In some areas, the concentrations of organochlorine pesticides in the sediment of the Ouémé River exceeded environmental quality standards and are reason for concern. The organophosphorous pesticide chlorpyrifos, used in a new formulation to protect cotton, was also identified.
Organochlorine pesticides identified in sediment samples included pp'-DDE, op'-DDD, pp'-DDD, op'-DDT, pp'-DDT, alpha-endosulfan, beta-endosulfan, endosulfan sulphate, alpha-HCH, beta-HCH, lindane, aldrin, dieldrin, endrin, telodrin, isodrin, cis- and trans-heptachlorepoxide, hexachlorbutadiene, hexachlorobenzene and octachlorostyrene. Except for one location, Tanéka-Koko, all areas were contaminated by more than 20 pesticides. In this study, organochlorine and organophosphorous pesticide residues were measured in more than 35 sediment samples collected on nine locations along the Ouémé River from upstream to downstream.
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