Assessment of Chromium Contamination in Aquatic Environments near Tannery Industries: A Portuguese Case Study

Environmental contamination from industrial activities remains a significant concern, with tanneries being major contributors of chromium (Cr) to aquatic systems. Cr, a heavy metal with multiple oxidation states, varies in toxicity and poses risks to both ecosystems and human health. In Portugal, the Alcanena region is particularly affected, hosting around 60 tanning industries. This study assessed total Cr levels in water from the Alviela River and Carvalho Stream, with particular focus on the impact of a local wastewater treatment plant (WWTP) that processes tannery effluents. Water samples were collected upstream and downstream of the WWTP discharge point. Analytical techniques included graphite furnace atomic absorption spectrometry and inductively coupled plasma optical emission spectroscopy, with a detection limit of 0.33 µg L−1. The highest Cr concentration (560 µg L−1) was found in the Carvalho Stream, downstream of the WWTP, confirming its contribution to local contamination. In the Alviela River, Cr concentrations ranged from 8 to 50 µg L−1 downstream of the WWTP, exceeding the predicted no-effect concentration for aquatic organisms and the safety limit for human consumption (25 µg L−1). These findings highlight, for the first time, the ongoing environmental impact of tannery effluents in this region and emphasize the urgent need for improved monitoring and pollution control measures.