Monitoring and Cancer Risk Assessment of Selected Persistent Organic Pollutants in Nairobi City, Kenya

Abstract

In Kenya, cancer is the third cause of death, after infectious and cardiovascular diseases. However, the causes of these high cancer burdens are not fully documented. Analysis of human milk from Nairobi City revealed possible human exposure to bioavailable persistent organic pollutants (POPs), which are known carcinogens. However, the levels, distribution, spatial variations and sources of these bioavailable POPs in the city are not known. The Stockholm Convention on POPs banned the use of eight organochlorine pesticides (OCPs), while USEPA monitors 16 priority polycyclic aromatic hydrocarbons (PAHs) in the environment, due to their carcinogenic risks. However, the cancer risks posed by environmental OCPs and PAHs to the residents of Nairobi City have never been assessed. Use of passive sampling and active sampling in monitoring of environmental OCPs and PAHs was evaluated. Levels of bioavailable OCPs and PAHs were monitored in air and selected surface waters in Dandora, Kibera, City Square, Industrial Area and Ngong Forest using semipermeable membrane devices (SPMDs) in a split-plot design replicated three times. SPMDs were exposed for 28 days, extracted by dialysis and analytes fractionated by solid phase extraction. The OCPs were analysed by GC-ECD while PAHs were analysed by GC-FID, and confirmed by GC/MS. Analysis of variance was done, and the data used to determine the distribution, spatial variation, sources, and cancer risks posed in Nairobi City. Active sampling gave lower (p≤0.05) pollutants‘ levels than passive sampling; indicating possible underestimation of their actual environmental levels in previous studies. Adoption of passive sampling in monitoring of environmental PAHs and OCPs is therefore recommended. Levels of gas-phase OCPs were 0.018 ng m−3−1.277ng m−3, while dissolved OCPs were <LOD−1297.667 ng m−3 in the order:Industrial area>𝐷𝑎𝑛𝑑𝑜𝑟𝑎>𝐾𝑖𝑏𝑒𝑟𝑎>𝐶𝑖𝑡𝑦 𝑆𝑞𝑢𝑎𝑟𝑒>𝑁𝑔𝑜𝑛𝑔′ 𝐹𝑜𝑟𝑒𝑠𝑡. Levels of gas-phase and dissolved PAHs were 0.104 ng m−3−1.773 ng m−3and <𝐿𝑂𝐷−1144.000 𝑛𝑔 m−3, respectively, in the order: City Square>𝐼𝑛𝑑𝑢𝑠𝑡𝑟𝑖𝑎𝑙 𝐴𝑟𝑒𝑎>𝐷𝑎𝑛𝑑𝑜𝑟𝑎>𝐾𝑖𝑏𝑒𝑟𝑎>𝑁𝑔𝑜𝑛g′Forest. The results suggested mixed sources of PAHs. Fugacity ratios revealed that Nairobi River contributed (p≤0.05) to atmospheric PAHs and OCPs in Nairobi City. The OCPs inhalation incremental lifetime cancer risks (ILCR) values were 2.3745 x10−13−1.6845 x 10−11 (adult) and5.5404 x 10−13−3.9306 x 10−11 (child), while the PAHs inhalation ILCR were 2.3573 x 10−11−1.5920 x 10−08(adult), and 5.5003 x 10−11−3.7147 x 10−08(child). The ILCR for both OCPs and PAHs in Nairobi City were below the acceptable risk levels, indicating that neitheratmospheric PAHs norOCPs in Nairobi City posed significant cancer risks to the residents