Abstract

       Nonylphenol (NP) a potent endocrine disrupting compound (EDC) is an eventual degradation product of nonylphenol polyethoxylates (NPE), primarily used in cleaning and industrial processes. The widespread use of NPE has founded the occurrence of NP in various environmental matrices such as water, sediment, air and soil. We have screened a few areas in the coastal region of Tamil Nadu. Our preliminary study documented NP concentration of 7.24 mg/L in Muttukadu back waters. Interestingly, Muttukadu waters is pristine ecosystem used as reference for control site; and now being affected by this compound. This is infact alarming and threat to aquatic life of these environment. The half-lives of these degraded products ranged from a few days to almost one hundred days. The compound has adverse effects on health and reproduction of aquatic animals as well as humans. This paper presents a preliminary review on the potential risks involved in the occurrence and accumulation of nonylphenol in various environmental matrices.

Introduction

         Continuous expulsion of pollutants into aquatic systems in India has prompted for a more sensitive assessment on the level of pollutants inhabiting in the environment. In recent ecotoxicological research, there is an increasing concern over the emerging endocrine disrupting compounds (EDCs) in the environment due to its multiple adverse effects especially on health and reproduction of wildlife animals and humans. They exert physiological effects by mimicking the natural hormone or by interfering with hormone's production, release, metabolism and elimination (Tabb and Blumberg, 2006). There are several natural and artificial EDCs, of them posing great risks are chemicals under the family of Alkylphenol ethoxylates (APEOs) such as nonylphenol ethoxylates (NPEs) and octylphenol ethoxylates (OPEs) with the former captivating 80% of the world’s market and octylphenol holds the remaining 20% (White et al., 1994). In the environment due to several natural factors, NPEs are broken down to Nonylphenol (NP) which has been predicted to be more harmful than the parent compound itself. Nonyl Phenol Ethoxylates are nonionic surfactants composed of ethylene oxide adduct of Nonyl Phenol. Nonyl Phenol Ethoxylates vary in physical appearance from clear or slightly hazy, colorless liquids to white solids, depending upon the level of ethoxylation. Nonylphenol ethoxylates can be used as such in a wide range of applications including emulsifiers and wetting agents, industrial, agricultural, institutional, textile dyeing and leather processing. They are also used in the processing of fuels, metals and petroleum. Substantial quantities of NP-containing compounds reach sewage treatment plants, where they degrade into several by-products, including NP (USEPA, 2010). For instance, un-reacted NP used as stabilizer in plastic may leach out and though this might not be a significant source of NP in the environment but it can direct route of exposure. When it comes in close contact with foods or if the plastics are ingested by aquatic organisms they may cause serious effects. Due to the endocrine potential of NP, the Oslo and Paris Commission for the Protection of the Marine Environment of the north-east Atlantic called for phasing out the use of NPEs in domestic cleaning agents by 1995 and in industrial cleaning agents by 2000. Following these recommendations, many countries, such as Sweden, Belgium, Great Britain, Germany, Holland, etc., have drastically limited the use of NPEs. Switzerland has completely banned the use of these substances (Zha et al., 2007). Due to its physico-chemical characteristics, NP accumulates and persists in sewage sludge, river sediments and other environmental compartments (OEHHA, 2009). Inspite of the wide use and ubiquity of EDCs in the environment, low and middle income countries often still lack the awareness on environmental monitoring (Duong et al., 2010). In India, rivers are intensively used for irrigation and drinking water, however, they often receive untreated wastewater and industrial effluents. To reduce river pollution, National River Conservation Plan (NRCP) of the Ministry of Environment and Forests, Government of India initiated a program to install sewage treatment plants (STPs) in most of the cities/towns close to major rivers (Ramaswamy et al., 2011). Although such steps are appreciable, it is odd that even now pollution controlling authorities in low and middle income countries do not have environmental guidelines on emerging chemicals such as APEOs, plasticizers, phthalates, pharmaceutical and personal care products (PPCPs), etc.

Environmental Occurrence

         The occurrence of NP in the environment is clearly correlated with human activities such as wastewater treatment, land filling and sewage sludge recycling. Maximum concentration of nonylphenol 7.24 ± 0.39 μg/L was recorded in Muttukadu back waters, Chennai, India (Raju et al., 2018). In many environmental studies related to pollution of coastal waters in Chennai, Muttukadu waters are used as reference for control site, which is now affected by this compound. In California, NP has been reported at concentrations of up to 0.89 micrograms per liter (μg/L) in freshwater bodies, over 1 μg/L in municipal treatment plant effluents, and up to 2.76 μg/L in coastal waters (OEHHA, 2009). When both these places are compared, Muttukadu in Tamil Nadu has 2 fold higher concentration of NP in its coastal waters, Similarly, a study by Selvaraj et al., (2014) detected nonylphenol concentrations in the Kaveri, Vellar and Tamiraparani rivers in the range of 2200ng/L, 22.4– 158ng/L and 1455ng/L with detection frequencies of 69, 100 and 54% respectively, which is higher than other countries. In Vellar river, NP showed increasing concentrations towards downstream locations. This trend indicates that locations with urban and industrial activities have elevated NP concentrations than rural and coastal environments. Mansson et al., (2008) reported that higher levels of NP in rivers may be associated with discharge of wastewater/effluents by textile, paper and leather industries. Furthermore, Hohne and Puttmann (2008) reported that NP in waste water are the prime degraded products of APEOs which are added in industrial detergents.

Risk assessment

         Surface waters serve as a direct or indirect sources of drinking water (Snyder and Benotti, 2010). The long term consumption of drinking water containing pollutants (chemicals) even at low concentration (ng/L level) may cause health hazards (Snyder and Benotti, 2010; Casals and Desvergne, 2011). The Kaveri and Tamiraparani rivers are the prime drinking water sources, for the population in and around the river. Human risk assessment performed in Kaveri and Tamiraparani rivers showed that concentration of NP was within the permissible limit (100 mg/L). However, regular monitoring is necessary because studies have reported potential toxicity of phenolic compounds in human cells at concentrations from ng/L to mg/L. Based on the reports potential toxicity of phenolic compounds to aquatic habitat, river Kaveri is more toxic than Tamiraparani followed by Vellar river.

Effects on Aquatic Life

         Studies have shown that a number of reproductive complications are induced in aquatic organisms due to NP such as, decreased gamete production and fertilization in medaka and zebrafish; reduced hatching of rainbow trout embryos; altered sex ratios in offspring of NP-exposed oysters; development of intersex trout, bream and frogs (i.e. offspring with characteristics of both sexes); lowered levels of the male sex hormone testosterone; effects on the testes, including decreased sperm production and increased uterine weight, suggesting that NP may affect females also.

Conclusion

         This toxicological profile on NP describes its effects on freshwater and marine life, humans, and laboratory animals. Although extrapolating the results of laboratory studies to environment is common, it would be preferable to analyze on free-living marine organisms. Unfortunately, there is a lacuna of these more-difficult studies. Most environmental concentration data are from fresh water systems. It would be useful to gather data on levels in marine environments, especially near municipal and industrial outfalls, landfills and other possible point sources of NP. The results support that the nonylphenol has now reached the level of affecting the aquatic lives. Nonylphenol can be predicted to increase in levels in all the possible matrices, even in human community in the near future as the compounds can moderately biomagnify.

Breaches

         Most of the environmental concentration data on NP are from fresh water systems; NP levels in the marine environment were not identified except around point and area sources. It is unknown how much plastics contribute to NP concentrations in the environment. Data on toxicity to marine organisms, especially free-living marine organisms, are lacking.

Recommendations

         Nonylphenol is very essential in several fields yet they have a distressing effects on organisms exposed. In this regard, several alternatives of nonylphenol have been suggested. They are alcohol ethoxylates, glucose based carbohydrate derivatives like, alkyl poly glucoside, glucamides, glucamine oxides which are less persistent and less toxic than nonylphenol. However, market acceptance of these alternatives depends on the cost and their performance in the intended use. To embrace a feasible pollution prevention strategy by eliminating NPEs (Nonylphenol poly ethoxylates) and substituting AEs (Alcohol ethoxylates) in detergent formulations would be much of a remedy. Further studies are necessary in order to evaluate on NP tissue levels in aquatic organisms for food chain exposure estimates. While reproductive and developmental effects in aquatic organisms are known to occur, other types of toxicity also need further research.

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