First evaluation of DDT (dichlorodiphenyltrichloroethane) residues and other Persistence Organic Pollutants in soils of Rwanda: Nyabarongo urban versus rural wetlands

• Published in: Ecotoxicology and environmental safety 2020-07, Vol.197, p.110574, Article 110574
• Main Authors: Umulisa, Viviane, Kalisa, Daniel, Skutlarek, Dirk, Reichert, Barbara
• Format: Article
• Language: English
• Subjects: East africa; Environment; Health risks; Organochlorines; Pesticides; Pollutants
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2020.110574

This study was the first to evaluate the occurrence, residue levels, spatial distribution and sources of DDT and other Persistence Organic Pollutants (POPs), which can be found in the Nyabarongo lower catchment (NLC) in Rwanda. These include Aldrin, Dieldrin, Endosulfan, Endrin, Hexachlorocyclohexane (HCH), Heptachlor, Heptachlorepoxide, Hexachlorobenzene (HCB), Isodrin, Methoxychlor, Mirex and Polychlorinated biphenyls (PCBs). A total of 108 soil samples were collected in the wetland area, both extracted and eluted with cyclohexane and analysed by GC-MS. The results indicated that DDT isomers and degradation products were major POPs and were detected in 44 samples (40%). Their detection frequency followed the order of 4,4′-DDE > 4,4' -DDT > 4,4' -DDD > 2,4' -DDT > 2,4' -DDD and 2,4' -DDE. Residues varied from non-detected (nd) to 120 μg kg−1 dry weight (dw), with a mean value of 3.93 μg kg−1 dw and a high variation (SD = 10.17 μg kg−1 dw). The degradation ratios confirmed both the historical and recent application of DDT and Dieldrin (0.53–18 μg kg−1 dw). Other detected POPs included PCBs in Kigali city which ranged from 0.1 to 0.21 μg kg−1 dw, confirming that the old contamination drifted from electric transformers. Aldrin (0.38–0.59 μg kg−1 dw); Heptachlor (0.14–0.19 μg kg−1 dw) residues probably reached the catchment through rain-washout. This study confirms that even though Rwanda banned the use of DDT and other POPs including pesticides (Aldrine, Chlordane, DDT, Dieldrine, Endrine, Heptachlor, Hexachlorobenzene, Mirex, and Toxaphene); Industrial products (Hexachlorobenzene and Polychlorobiphenyl PCBS) and unintentional sub-products, since 2002, some of above products are still used in random areas (e.g: DDT, Dieldrin). The highest residues were detected close to Lake Muhazi and areas surrounding Kigali city. This study recommends full evaluation of human health and ecological risks from exposure to DDT. Additionally, the National Implementation Plan (NIP) for the Stockholm Convention to eliminate POPs should be reinforcement through strengthening the market control and educational programs. •The degradation status of DDT and Dieldrin confirm both their historical and recent application in the study area.•Lake Muhazi neighboring is highiest in residues, related to non and low-degraded DDT, suggesting its recent & illegal use.•Regular evaluation of residues is vital to prevent risk of crops, soil organisms, livestock and fish contamination.•Soil sample