Long-term persistence of sedimentary copper contamination in Lake Orta: potential environmental risks 20 years after liming

Lake Orta, northern Italy, has suffered from severe copper pollution and human-induced acidification between the 1920s and the 1990s because of discharges from a rayon factory and electroplating industries located in its water basin. Following liming operations in the late 1990s, the chemical quality of the water column has been restored and signs of, still ongoing, biological recovery observed. Examination of two sediment cores collected close to the main historical Cu discharge and in the central part of the Lake shows that Cu concentrations in the uppermost layers of bottom sediments remain 10 to 40-fold higher than background levels. Past studies demonstrated the toxic potential of Lake Orta sediments to a variety of organisms at Cu concentrations comparable to present ones. Comparison with published results suggests that current level of Cu contamination may still pose a risk to sediment-ingesting organisms and slow down further ecological recovery of Lake Orta. Particular attention should be given to understand the effects of dietary ingestion of Cu from sediments which, unlike in previous ecotoxicological studies, may now represent the main route of Cu exposure for sediment-ingesting benthic organisms.