|dc.description.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.||en