Acute and chronic toxicity of cationic polyquaterniums of varying charge density and molecular weight to Daphnia magna and Ceriodaphnia dubia.

Abstract

Cationic polymers have the unique ability to neutralize negative charge with practical applications in personal care products, such as shampoos, conditioners, contact lens solutions, and as flocculants in wastewater treatment processes. Cationic polymers are a diverse class of materials varying in structural composition, cationic charge density (CD), and molecular weight (MW). In this study, we investigated three classes of polyquaternium cationic polymers (PQ-6, PQ-10, PQ-16) of varying CD and MW to characterize their toxicity to aquatic invertebrates. Although safety studies and environmental risk assessments have been conducted to support the use of polyquaterniums, further research was needed to adapt standard toxicity assays to account for the unique properties of cationic polymers. Standard acute OECD 202 assays were conducted with Daphnia magna and Ceriodaphnia dubia to explore relative species sensitivity. PQ-6 exhibited toxicity ranging from 0.09 to 2.50 mg/L, PQ-10 ranged from 21.29 to >1000 mg/L, and PQ-16 ranged from 0.05 to 14.91 mg/L. Toxicity was positively correlated with CD and not correlated with MW or polymeric backbone. C. dubia were more sensitive to PQ exposure than D. magna, and this trend was consistent across all exposures. Organic carbon (humic acid and algae) was found to mitigate PQ toxicity in a dose-dependent manner, highlighting the importance of robust exposure characterization when assessing environmental risk. Chronic reproductive toxicity assays were conducted on high and low MW PQ-6 materials with observed significant decreases in days to first clutch, average offspring per clutch, and body length. Robust acute to chronic (ACR) values were derived.