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 ∼ 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.

Assessment of biomarkers for contaminants of emerging concern on aquatic organisms downstream of a municipal wastewater discharge.

Contaminants of emerging concern (CECs), including pharmaceuticals, personal care products and estrogens, are detected in wastewater treatment plant (WWTP) discharges. However, analytical monitoring of wastewater and surface water does not indicate whether CECs are affecting the organisms downstream. In this study, fathead minnows (Pimephales promelas) and freshwater mussels Pyganodon grandis Say, 1829 (synonym: Anodonta grandis Say, 1829) were caged for 4 weeks in the North Saskatchewan River, upstream and downstream of the discharge from the WWTP that serves the Edmonton, AB, Canada. Passive samplers deployed indicated that concentrations of pharmaceuticals, personal care products, an estrogen (estrone) and an androgen (androstenedione) were elevated at sites downstream of the WWTP discharge. Several biomarkers of exposure were significantly altered in the tissues of caged fathead minnows and freshwater mussels relative to the upstream reference sites. Biomarkers altered in fish included induction of CYP3A metabolism, an increase in vitellogenin (Vtg) gene expression in male minnows, elevated ratios of oxidized to total glutathione (i.e. GSSG/TGSH), and an increase in the activity of antioxidant enzymes (i.e. glutathione reductase, glutathione-S-transferase). In mussels, there were no significant changes in biomarkers of oxidative stress and the levels of Vtg-like proteins were reduced, not elevated, indicating a generalized stress response. Immune function was altered in mussels, as indicated by elevated lysosomal activity per hemocyte in P. grandis caged closest to the wastewater discharge. This immune response may be due to exposure to bacterial pathogens in the wastewater. Multivariate analysis indicated a response to the CECs Carbamazepine (CBZ) and Trimethoprim (TPM). Overall, these data indicate that there is a 1 km zone of impact for aquatic organisms downstream of WWTP discharge. However, multiple stressors in municipal wastewater make measurement and interpretation of impact of CECs difficult since water temperature, conductivity and bacteria are also inducing biomarker responses in both fish and mussels.

Effects of anionic polyacrylamide products on gill histopathology in juvenile rainbow trout (Oncorhynchus mykiss).

Anionic polyacrylamide (PAM) products are commonly used to remove suspended materials from turbid waters and to help mitigate soil erosion. In the present study, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to 3 mg/L to 300 mg/L of 10 commercially available PAM products (Clearflow Water Lynx Polymer Log and Clearflow Soil Lynx Granular Polymer; Clearflow Enviro Systems Group), and gill histological parameters were measured following either 7 d or 30 d of polymer exposure. A cationic polymer product (≤0.38 mg/L MagnaFloc 368; Ciba Specialty Chemical) was also tested for comparison. Mild gill lesions were observed in fish exposed to polymer products. Lamellar fusion, interlamellar hyperplasia, epithelial lifting, mucous cell metaplasia, and cell counts of epithelial swelling and necrosis/apoptosis were minimal in fish exposed to environmentally relevant concentrations of anionic polymer (≤30 mg/L). Gill morphology was largely unaffected by exposure to concentrations up to 300 mg/L of many PAM products. Several anionic polymer products noticeably affected gill tissue by increasing epithelial hypertrophy, interlamellar hyperplasia, mucous cell metaplasia, and the frequency of necrotic cells. The severity of the lesions lessened with time, suggesting that fish may have experienced a short-term irritant effect. Similar levels of gill pathology were frequently observed in fish exposed to cationic polymer MagnaFloc 368 despite the concentration being 1000-fold lower than that of the PAM products. These observations highlight the increased toxicity of cationic polymers to aquatic life compared with anionic PAMs.