Predominantly lithogenic chromium and nickel elevate sediment guideline quotients and exposure screening in a subtropical African water supply reservoir
5 affiliations
- 1Centre for Invasion Biology, School for Climate Studies, Stellenbosch University, Stellenbosch, South Africa
- 2Department of Geography and Environmental Sciences, University of Venda, Thohoyandou, South Africa
- 3South African Institute for Aquatic Biodiversity, Makhanda, 6140 South Africa
- 4The Wilderness Project Foundation, Johannesburg, South Africa
- 5Aquatic Systems Research Group, Department of Water and Sanitation, University of Limpopo, Polokwane, South Africa
Abstract
Reservoir sediments accumulate potentially toxic elements from both catchment weathering and human activity, and concentration-based indices regularly confound the two. We evaluated this distinction in the Nandoni Reservoir, a water supply impoundment along the Luvuvhu River, South Africa. Surface sediment (0 to 5 cm) was collected using an Ekman grab at 21 sampling sitessite in October 2023, at the end of the dry season, and 26 elements were quantified by inductively coupled plasma mass spectrometry (ICP–MS). Chromium, nickel, copper and lead covaried strongly with aluminium, with element to aluminium ratio coefficients of variation of 0.36 or less. Aluminium normalised enrichment factors for Pb, Zn, Cd, As and Hg were at or below crustal proportions, whereas Cr, Cu and Ni were elevated relative to average shale. These patterns are consistent with predominantly lithogenic control, but do not by themselves establish source dominance and do not exclude diffuse anthropogenic inputs. Chromium exceeded the consensus probable effect concentration at 14 sampling sitesite and nickel at 13, and the mean probable effect concentration quotient ranged from 0.18 to 0.85. Exceedance of this kind indicates screening level concern rather than demonstrated ecological effect. Deterministic hazard indices were 0.07 to 0.34 for an adult maintenance worker and 0.36 to 1.67 for a child with incidental shoreline contact, exceeding one at nine sites for the child, falling to three sites when chromium was treated as Cr(III) rather than as the conservative upper bound Cr(VI). Replacing average shale with a pre–industrial reference inflated the pollution load index 4.0 fold, driven almost entirely by Ni, Cu and Cr. Source attribution, ecological screening and exposure assessment must be reported as separate lines of evidence.
Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s10653-026-03558-1.
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BibTeX
@article{dalu2026predominantly,
title = {{Predominantly lithogenic chromium and nickel elevate sediment guideline quotients and exposure screening in a subtropical African water supply reservoir}},
author = {Tatenda Dalu and Farai Dondofema and Chad Keates and Linton F. Munyai},
journal = {Environmental Geochemistry and Health},
year = {2026},
month = oct,
doi = {10.1007/s10653-026-03558-1},
url = {https://doi.org/10.1007/s10653-026-03558-1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Predominantly lithogenic chromium and nickel elevate sediment guideline quotients and exposure screening in a subtropical African water supply reservoir
AU - Tatenda Dalu
AU - Farai Dondofema
AU - Chad Keates
AU - Linton F. Munyai
PY - 2026
DA - 2026/10/26
JO - Environmental Geochemistry and Health
DO - 10.1007/s10653-026-03558-1
UR - https://doi.org/10.1007/s10653-026-03558-1
AB - Reservoir sediments accumulate potentially toxic elements from both catchment weathering and human activity, and concentration-based indices regularly confound the two. We evaluated this distinction in the Nandoni Reservoir, a water supply impoundment along the Luvuvhu River, South Africa. Surface sediment (0 to 5 cm) was collected using an Ekman grab at 21 sampling sitessite in October 2023, at the end of the dry season, and 26 elements were quantified by inductively coupled plasma mass spectrometry (ICP–MS). Chromium, nickel, copper and lead covaried strongly with aluminium, with element to aluminium ratio coefficients of variation of 0.36 or less. Aluminium normalised enrichment factors for Pb, Zn, Cd, As and Hg were at or below crustal proportions, whereas Cr, Cu and Ni were elevated relative to average shale. These patterns are consistent with predominantly lithogenic control, but do not by themselves establish source dominance and do not exclude diffuse anthropogenic inputs. Chromium exceeded the consensus probable effect concentration at 14 sampling sitesite and nickel at 13, and the mean probable effect concentration quotient ranged from 0.18 to 0.85. Exceedance of this kind indicates screening level concern rather than demonstrated ecological effect. Deterministic hazard indices were 0.07 to 0.34 for an adult maintenance worker and 0.36 to 1.67 for a child with incidental shoreline contact, exceeding one at nine sites for the child, falling to three sites when chromium was treated as Cr(III) rather than as the conservative upper bound Cr(VI). Replacing average shale with a pre–industrial reference inflated the pollution load index 4.0 fold, driven almost entirely by Ni, Cu and Cr. Source attribution, ecological screening and exposure assessment must be reported as separate lines of evidence. Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s10653-026-03558-1.
SN - 0269-4042
SN - 1573-2983
ER -