Occurrence, Environmental Fate and Toxicological Effects of Nonylphenol Ethoxylates in Aquatic Organisms: A Comprehensive Review

Nonylphenol ethoxylates (NPEs) are one of the major non-ionic surfactants that have been used extensively in a wide variety of industries such as detergent manufacture, textile processing, pesticide manufacturing and cleaning products. The large-scale global use of NPEs is the main reason for their continuous and significant discharge into the water bodies through the effluents from the municipal and the industrial wastewater treatment plants. Environmental monitoring data show that the concentrations of total NPEs in untreated sewage are usually between 1 and 12 mg L⁻¹, while the levels of NPEs in surface waters that are discharged with treated effluents are between 0.05 and 5.0 µg L⁻¹. One of the major environmental concerns linked to NPEs is their partial biodegradation, where these substances are transformed only slightly by microorganisms producing lesser chain ethoxylates and eventually nearly nonylphenol (NP), a metabolite significantly more persistent and toxic than the parent compounds. Nonylphenol is a highly hydrophobic compound with octanol-water partition coefficients (log Kₒw) of about 4.5 to 4.8, thus leading to strong bioaccumulation in aquatic organisms, which has been observed with bioconcentration factors of 1,000 to 10,000 depending on the species and environmental conditions. Long-term exposure to NPEs and their degradation products at environmentally relevant concentrations causes wide-ranging adverse effects like unpleasant smell, endocrine system disruption, reproductive failure, oxidative stress, and δ2H and δ18O ratios indicative of developmental abnormalities in fish and invertebrate populations. This in-depth review gives a critical analysis of the prevailing understanding of the environmental occurrence, fate processes, and bioaccumulation of NPEs and their transformation products in aquatic organisms, particularly focusing on the endocrine-disrupting properties that are a risk even at very low environmental concentrations. Keywords: Nonylphenol Ethoxylates, Substance, Environmental Fate, Aquatic Organisms