Assessing Multi-Source Chemical Pollution and Sediment Toxicity in Northern Patagonian Streams

The Valcheta Stream, located in an endorheic basin in Northern Patagonia, Argentina, is a remote system increasingly exposed to diverse anthropogenic pollutants. To evaluate sediment-associated toxicity, we collected composite samples (right bank, left bank, and mid-channel) from three sites with different contamination sources–an agricultural impact zone, an urban-influenced area, and a sewage-affected reach–along with an upstream reference site. Lyophilized sediments were transported under cooled conditions to Germany and Switzerland, where we applied an integrated suite of physiological, behavioral, and molecular biomarkers using amphipods of the genus Gammarus.

Amphipods were collected from the Main River and acclimated for 5–10 days before exposure. Experiments followed OECD/ISO guidelines employing four sediment treatments and a negative control consisting of six replicates, six organisms per 250-ml aerated beaker at 16 °C (total 30 beakers, 180 organisms). Behavioral responses were measured at 24, 48, and 96 h with the ToxmateLab system (ViewPoint, Lyon), using alternating light–dark cycles. Automated analyses identified distinct activity patterns. Preliminary assessments of hyperactivity and hypoactivity revealed clear deviations from baseline locomotion in organisms exposed to sediments from the more impacted sites. Urban sites produced the greatest deviations, potentially suggesting a combination of stressors. Additional parameters, including activity time and average and maximum speed at light and dark conditions, are currently being evaluated in an attempt to obtain a higher sensitivity to these effects.

Following behavioral tests, organisms were frozen at –70 °C for subsequent biochemical and proteomic analyses. Planned endpoints include oxidative stress markers (lipid peroxidation via TBARS, antioxidant and metabolic enzyme activities) and mass-spectrometry-based proteomics with label-free quantification on a Thermo Astral instrument operated in DIA mode.

By integrating behavioral, biochemical, and proteomic biomarkers, this study seeks to identify highly sensitive early-warning indicators of sediment-associated toxicity in the Valcheta Stream under multiple anthropogenic pressures. The combined approach will allow us to disentangle complex stressor effects and detect sublethal impacts well before population- or community-level responses become evident. The resulting indicator set is intended to support regulators and watershed managers in strengthening chemical-risk prevention, improving sediment-quality assessment, and safeguarding freshwater biodiversity in Patagonian ecosystems facing accelerating environmental change.