Assessment of heavy metals concentration in ash from incinerators and its environmental implication in Nairobi, Kenya

Abstract

Incineration is used to destroy and reduce the amount of hazardous chemical and biological wastes consequently lowering their potential infectious and toxic properties. Incineration byproducts like ash are a potential risk to human health and the environment. The problem is growing with an ever-increasing number of hospitals, clinics, diagnostic laboratories and research laboratories in the City of Nairobi, Kenya. The objectives of this study were to assess the heavy metals concentration in bottom ash and their ecotoxicological effects in twelve major incinerators in Nairobi. A baseline survey on the environmental impacts of heavy metals and incineration methods was conducted between June and August 2007 at twelve major incinerators in Nairobi. Empirical field observation and field-level data collection through inventory, questionnaire survey and formal and informal interviews were administered from October to December 2007 after prior consenting of about 100 respondents. A structured questionnaire was designed to collect information on the respondents' socio-demographics, duration of stay in the proximity of incineration, attributable symptoms of heavy metal toxicity. A number of in-depth interviews were conducted to elaborate understanding the existing management practice of wastes, the potential hazards and morbidity due to heavy. metal exposure. Quantitative data was analyzed, mainly with simple descriptive statistics. A total of 36 bottom ash samples were collected during the study period in three different visits from all the incinerators. Ethical approval from respective institutional and government regulatory authorities was granted. The ashes were analyzed in triplicate for the presence of Arsenic, Cadmium, Chromium, Copper, Mercury and Lead USIng Atomic absorption spectrometry (AAS) and detectable levels of all were found in bottom ash. One sample t- test (ANOYA) analysis revealed highly significant toxicity in all the elements. Chromium had the highest concentrations t= 11.718, mean difference (MD) = 94.83mg/kg, CI (77 .0206-112.6460) at p <0.05(Table 3) and Copper had the lowest concentrations but showed greatest variation among the sites, t=2.819, mean difference (MD) = 95.67 mg/kg, CI (20.9852- 170.3481) at P<0.05(Table 3) while Mercury had the smallest variation among all the sites, t = 8.529, mean difference (MD) = 31.42mg/kg, CI (23.3095-39.5238). Heavy metal concentrations exceeded the permitted values of GB 18918-2002 Ecotoxicological impacts and apparent toxicology indices on various body systems of the respondents were scored as Musculosketal system (21%), Dermatological (19%), Respiratory (18%), Gastrointestinal (13%), Cardiovascular (11%), Reproductive (9%) and Nervous (9%) respectively. Open dumping was the main disposal method in use. Comprehensive evaluation of the environmental impacts of incineration pollution is necessary. Improvement on the design of incinerators is paramount with better management practices on proper disposal of bottom ash is needed to minimize the adverse environmental impact.