Toxicity and tissue accumulation of 4-nonylphenol in the catfish Heteropneustes fossilis with a note on prevalence of 4-NP in water samples

4-nonylphenol (4-NP) a persistent and ubiquitous xenoestrogen with endocrine-disrupting activities, is present in varying concentrations in wastewater, ground water, treated drinking water and sediments. It is a biodegradation product of alkylphenolethoxylates used widely as a nonionic surfactant. In the present study, the presence of 4-NP in water samples and its toxicity and tissue accumulation were investigated in an air-breathing catfish Heteropneustes fossilis. The concentration of 4-NP varied between 12.40 ± 1.11 μg/L and 16.29 ± 1.18 μg/L in water samples drawn from river Ganga and river Varuna at 3 different sites that witness high anthropogenic activities or near a city wastewater treatment efflux point. Stored tap water contained 4-NP albeit at a low level (3.9 ± 0.23 μg/L). The median lethal concentrations (LC50) of 4-NP were 1600 μg/L and 1632 μg/L, respectively, in the gonad resting phase and gonad active (preparatory) phase. The concentration of 4-NP added to fish holding water was reduced by 67% over 10 hr of fish introduction suggesting a faster accumulation of the toxicant by fish. In a chronic study spanning 60 days, 4-NP added to the water was accumulated by tissues in a concentration (64 and 160 μg/L) and exposure time (15, 30, 45 and 60 days) – dependent manner. Brain accumulated the highest concentration of 4-NP while muscle showed the lowest uptake. Gill, liver, kidney, ovary and plasma showed intermediate ranges of accumulation. HPLC chromatogram profiles showed that 4-NP was metabolized in all tissues (brain, liver, kidney, gill and ovary) except muscle and plasma. A distinct seasonality of 4-NP was not discerned in this study, probably due to the fact that a steady state level was not reached up to 60 d of exposure. The study concludes that 4-NP is an environmentally relevant toxicant and the catfish has a high tolerance level, which may be due to the fact that 4-NP is metabolized by many tissues during its elimination.