Distribution of heavy metals in surface water and sediments of the Coata River Basin, Peru: Seasonal variability and ecological risk assessment

Abstract

Mining, urban wastewater discharge, and intensive agriculture have degraded freshwater quality across the Andean Altiplano, yet integrated multi-parameter assessments remain scarce for high-altitude tributaries of Lake Titicaca. This study evaluated the spatial and seasonal distribution of seven heavy metals (As, Cd, Cr, Cu, Hg, Pb, and Zn) in surface water and sediments, along with physicochemical and microbiological parameters, across 11 stations in the Coata River Basin (Puno, Peru). Dissolved arsenic exceeded the WHO guideline (0.01 mg L?¹) at 10 of 11 stations. In sediments, mean Zn (337.9-400.5 mg kg?¹), Pb (67.7-81.2 mg kg?¹), and As (41.9-43.3 mg kg?¹) surpassed the Threshold Effect Level at every site. Cadmium contamination factors reached very high values (CF up to 15.67), and the geo-accumulation index classified several stations as strongly to extremely polluted (I_geo up to 3.38). The potential ecological risk index ranged from 111.8 to 627.1, with station P-6 reaching very high risk during the dry season. The Torococha–Coata confluence (P-7) emerged as the most degraded reach, with dissolved oxygen of 0.52 mg L?¹ and total coliforms of 1.4 × 10? MPN 100 mL?¹. Sediment contamination intensified during the dry season due to reduced dilution. Mining waste, untreated effluents from Juliaca, and agricultural runoff were identified as the principal contamination sources. Building on this diagnosis, this study proposes a prioritized, phased management strategy coupling source control of mining and urban effluents, sediment-focused remediation at hotspots, and permanent seasonal monitoring to guide near-term pollution mitigation in the basin.