Chromium bioavailability in aquatic systems impacted by tannery wastewaters. Part 2: New insights from laboratory and in situ testing with Chironomus riparius Meigen (Diptera, Chironomidae)

Chromium is widely used as a tanning agent and can become a contaminant of concern in aquatic ecosystems receiving discharges from industrial or artisanal tanning activities. In a companion study, we showed that Cr discharged by tanneries was bioavailable to indigenous chironomids with accumulation via sediment ingestion likely to represent the predominant exposure route. However, Cr accumulation by chironomids did not directly reflect the degree of sediment contamination and the potential adverse effects of Cr accumulation on chironomids were not evaluated. In the present study, chironomids were exposed to homogenised, field-collected sediments in the laboratory and to intact sediments in situ using a customized caging system. Chromium concentrations were assessed in sediments, exposed larvae of laboratory-reared Chironomus riparius and overlying waters of in situ cages. Experimental results of Cr bioaccumulation were compared with expected Cr body burden in chironomids calculated using biodynamic modelling. Our data provided strong support to the hypothesis that Cr bioaccumulation in the field is specifically controlled by the deposition of contaminated suspended particulate matter (SPM) containing a pool of Cr readily bioavailable to surface deposit feeders. Considering freshly deposited SPM as an additional route of exposure for surface deposit feeders leads to a good agreement between the modelling and experimental results. Additionally, a Cr body burden of about 77 μg g−1 d.w. was identified as a tentative threshold above which effects on the growth of C. riparius may appear. While both laboratory and in situ experiments provide evidence for the availability of Cr in aquatic system impacted by tannery wastewaters, standard laboratory exposure conditions may miss additional exposure routes in the field and underestimate possible adverse effects on benthic organisms. [Display omitted] •A pool of bioavailable Cr occurs in aquatic systems impacted by tannery wastewaters.•Laboratory tests underestimate Cr bioavailability and potential effects to C. riparius.•C. riparius caged in situ accumulate Cr via ingestion of freshly deposited particulate matter.•In situ tests provide indications about Cr bioaccumulation by indigenous chironomids.•A threshold of 77 μg g−1 d.w. is calculated for Cr effects on the growth of C. riparius.