Ammonia and chromate interaction explains unresolved Hyalella azteca mortality in Flanders’ sediment bioassays

Agricultural, industrial and household chemicals are emitted in large rivers along populated areas, transported by water deposited sediments, posing (eco)toxicological risks. Sediments have received less attention than surface waters, likely because of the intrinsic complexity interactions between sediment constituents complicating correct framing exposures. Sadly, thorough assessment situ behavior bioassays is often not practical. Alternatively, we related physicochemical properties sediments from field testing to results bioassays. The case study covers Flemish (incl. Scheldt Meuse) mortality Hyalella azteca, a sensitive bio-indicator. Though variable across Flanders’ main bodies, heavy metals ammoniacal nitrogen dominate observed toxicity according toxic unit (TU) assessments. Depending on body explain 50 90% variance H. azteca mortality, substantially more previous ecotoxicity studies. We attribute remaining potential incoherently documented biophysicochemical concentrations non-target biocides, conditions/set-ups and/or species variabilities. discuss relative influence metals/metaloxides, (e.g. fertilizer), polycyclic aromatics organochlorides. highlight both direct indirect mechanisms. note synergetic mixture effects chromium. Such synergy may be phenomenological ‘standard’ aerobic bioassays, prove complementary method alongside ‘acid-volatile sulfide test’ effectively link concentration toxicity. Future ought include variation sampling locations batch Our approach enables managers interpret their monitoring data converting prioritize substances that contribute most.