Association of Carcinogenic Heavy Metals in Foods, With Colorectal Cancer, In Nyambene, Meru County, Kenya,

Abstract

Colorectal cancer is a growing public health concern in Kenya, especially in the Kiegoi sub-location of Nyambene region where incidence rates are rising without clear etiology. This study aimed to quantify arsenic, cadmium, chromium, mercury and lead in staple foods from Kiegoi and explore their association with colorectal cancer incidence in the area. Cross sectional retrospective review of Meru Teaching and Referral Hospital oncology department records from 2018-2024 was conducted which limits the causal inference of heavy metals in colorectal cancer. Samples of beans, arrowroots, potatoes and maize were collected using simple randomized stratified sampling from each of the five agro- ecological zones in Kiegoi. The samples were then digested with nitric v acid, perchloric acid and hydrochloric acid and analyzed by inductively coupled plasma mass spectroscopy (ICP-MS). The overall crude incidence of colorectal cancer in Kiegoi was 1211 per 100,000 of the population. The age specific standardized rate (WHO standard population) was599 per 100,000 of the population. Cadmium levels were significantly below regulatory thresholds (below FAO/WHO limits) in all foods. Mercury and chromium levels exceeded limits in 100 % of the samples; arsenic and lead exceeded levels in 50 %. Multivariate logistics regression identified lead (OR=17.7), mercury (OR=3.5) and arsenic (OR=2.5) as significant predictors for colorectal cancer. Cadmium showed a negative association while chromium’s effect was marginal. Widespread contamination by mercury chromium and lead in staple foods most likely contributes to Nyambene’s colorectal cancer burden. Policy measures should include routine environmental surveillance, soil remediation and targeted public health screening.