Heavy Metals in Nearshore Marine Sediments Along the Coast of Ilo (Moquegua, Peru): Spatial Patterns and Seasonal Variation

Coastal sediments integrate contaminant inputs over time and are widely used to assess anthropogenic pressure, yet baseline data remain scarce along the Peruvian coast. Metal concentrations and their associated ecological risk were assessed in nearshore marine sediments along 16 km of coast at Ilo (Moquegua, Peru), across five stations subject to contrasting anthropogenic pressures and three sampling campaigns (n = 15). Concentrations were determined by energy-dispersive X-ray fluorescence on the <63 µm fraction, and evaluated through contamination and ecological risk indices and comparison with sediment quality guidelines. Six of the eleven elements determined were quantified above detection limits; Ag, As and Cd fell below and were excluded. Only Cu and Ni were clearly enriched relative to background (mean Igeo 2.37 and 1.78), and both exceeded their probable effect level in most samples. Cu peaked at the station facing a copper smelter, whereas Ni was highest where no discharge occurs, a contrast also reflected in an exploratory principal component analysis. Contamination load exceeded background throughout, and the station ranking held under three independent background scenarios. Seasonal variation was significant only for Fe and Mn (Friedman, p = 0.022), the two elements without enrichment, and did not alter the spatial pattern of contamination. Cu in the area facing the smelter is therefore the main contamination concern along this coast.