Hypoxemia as the mechanism of acute cationic polymer toxicity in rainbow trout and prevention of toxicity using an anionic neutralizing polymer

Industrial operations such as surface mining, road building, and aggregate washing result in high concentrations of suspended particles (Total Suspended Solids; TSS) in surface waters which must be treated prior to discharge into fish-bearing waters. A common industrial practice is to add flocculants to improve the efficacy and speed of TSS sedimentation. A significant environmental issue even small amounts of uncomplexed cationic polymer coagulant/flocculant remaining in treated water is highly toxic to fish at very low concentrations (LC50 similar to 0.3 mg L-1). Fingerling trout (Oncorhynchus mykiss) were exposed to (1) a cationic flocculant (Water Lynx 800 (WL800), (2) a Clearflow neutralizing polymer (CN369), and (3) a combination of WL800 and CN369 at various ratios with measured LC50 as an index of toxicity. Acute toxicity was entirely reversed by addition of the neutralizing polymer at WL800:CN369 ratios >1:1.5 mg/L. Furthermore, we demonstrate that the proximal mechanism of acute cationic polymer toxicity is hypoxemia due to accumulation of polymer on the gill epithelia rather than gill damage. Exposure of 0.5 mg/L WL800 reduced oxygen consumption by >50% reduction by 12 h and this was accompanied by significantly increased blood, brain, and liver [lactate] and [glucose]. The development of an inexpensive amelioration technique preventing cationic polymer toxicity is a significant advancement in surface and industrial water treatment to prevent cationic polymer mediated fish kills.

Automated summary

Industrial operations lead to high concentrations of suspended particles in surface waters, which need to be treated before being discharged into fish-bearing waters. Adding flocculants is a common practice to improve the sedimentation of these particles. However, even small amounts of uncomplexed cationic polymer coagulant/flocculant remaining in the treated water can be highly toxic to fish. This study found that the toxicity of the cationic polymer is due to its accumulation on the gill epithelia, leading to hypoxemia in fish. The toxicity can be reversed by adding a neutralizing polymer.