TRACE ELEMENTS AND MERCURY IN FISH AND LEAFY VEGETABLES FROM THE ARUWIMI RIVER (BANALIA AND BASOKO TERRITORIES, DEMOCRATIC REPUBLIC OF THE CONGO): A BASELINE SURVEY WITH EXPLORATORY MULTIVARIATE ANALYSIS

Abstract

Fish and leafy vegetables supply most of the animal protein and greens eaten along the Aruwimi River, yet nothing is known about their trace-element content. We analysed the dorsal muscle of ten fish (nine species) and the leaves of cassava (Manihot esculenta) and sweet potato (Ipomoea batatas) collected in the Banalia and Basoko territories (Tshopo Province) during the 2025 dry season. Fourteen elements were determined by ICP-MS, and total mercury separately. Scandium, nickel, thorium and uranium were found only in the leaves. Most elements were strongly right-skewed; Hg was the only one whose raw distribution did not depart from normality (Shapiro–Wilk p = 0.40). The leaves contained more Cr, Mn and Co than the fish (exact Mann–Whitney p = 0.030, the smallest value attainable with two leaf samples), whereas As was higher in fish. Spearman correlations and an exploratory principal component analysis separated a Cr Mn–Fe–Co–Zn group, which mostly distinguished leaves from fish (PC1, 44.6% of the variance), from a Hg–Cd–Pb axis (PC2, 18.3%). Mercury in fish ranged from 0.52 to 4.44 mg/kg dry weight, i.e. an estimated 0.10–1.11 mg/kg wet weight; three to four of the ten fish exceeded the 0.5 mg/kg guideline, depending on the moisture assumed. One Pollimyrus isidori specimen returned 1,250 mg/kg Pb, a biologically implausible value that must be re-analysed; Pb in every other sample was 0.55 mg/kg dry weight or less. With twelve samples and no replication within species, these data are a first baseline rather than a risk assessment, but they make a case for targeted monitoring of Hg in fish from this part of the Congo Basin, whose upper course drains artisanal gold-mining areas of Ituri.