Nonylphenol : Properties , legislation , toxicity and determination

ABSTRACT This paper aims to gather and discuss important information about nonylphenol, such as physical chemistry properties, toxicity and analytical methods in various matrices. As a degradation product of ethoxylated alkylphenols, nonylphenol presents a higher degree of reactivity than its precursor. Due to its harmful effects on the environment, use and production of nonylphenol has been banned in European Union countries, alongside their precursors. The guide on quality of drinking water (USEPA) recommends a maximum concentration of 28 μg L for fresh water. In Brazil, there is no clear legislation containing values of maximum concentration of nonylphenol. Due to this lack of regulation, a continuous monitoring is necessary of this pollutant in environmental samples. This paper aims to encourage further studies on nonylphenol, seen as a critical environmental pollutant. For proper monitoring is necessary to have reliable analytical methods and easy to perform in routine analysis.


INTRODUCTION
Nowadays, the growing concern over water resources availability is justified by its key role in the socioeconomic development of humanity.Availability which is affected not only by water scarcity in some regions, or the increase in world demand, but also by the depreciation of its quality.Considering the uncontrolled growth of cities and human activities in the surrounding watershed, it is worth noticing the increased pollution of surface and groundwater (Rebouças 2001, Vianna 2015, Tundisi 2008).In Brazil, even with investments in sewage systems and treatment plants, only a small portion of the sewage volume generated by cities is effectively treated before reaching the rivers.The release of sewage into water bodies without any treatment is one of the main causes for depreciation of water quality.The absence of adequate basic sanitation compromises the primal use of this resource, the public supply.Such context imposes a continuous need for finding even further sources, more complex and more expensive chemical treatments to ensure availability of drinking water (Tucci 2008).FREDERICO G. DE ARAUJO et al.
A general concern has been raising worldwide about the contamination of the environment (air, soil, forests, animals, rivers and oceans by chemicals from industrial activities, mineral exploration and agricultural exploitation) and its relation to the recent increase of congenital malformations, asthma, cancer and neurological and behavioral disorders in children (Godoi et al. 2003, Mello-da-Silva andFruchtengarten 2005).
The concern about the contamination of surface and underground water systems with pesticides has grown in the world.In industrialized countries, the Green Revolution of the 1960s significantly increased agricultural productivity due to the expansion of sown area, mechanization, pest control, among others.For pest control, the massive use of pesticides was necessary, dangerous chemicals used to repel or kill rodents, fungi or insects potentially harmful to intensive agriculture.These extensively used chemicals, at first sight, bring a great benefit to human health, by increasing agricultural productivity.On the other hand, many of those first-generation pesticides are harmful to the environment.Some of them can persist in soils and aquatic sediments, bioaccumulate in the tissues of invertebrates and vertebrates, moving in trophic chains, and affect top predators (Mnif et al. 2011).
After the Second World War the sale and trading of chemicals, such as fertilizers, pesticides and insecticides increased sharply.This increase was justified by industrial development and the need to supply the demand of the population for food and to improve the quality of crops (Colborn et al. 1994, El-Shahawi et al. 2010).Meanwhile, the problem of environmental pollution has emerged, particularly regarding water, soil and air .The organic compounds released into the environment, or formed from the degradation of other compounds, generally present a high toxicity that may chronically alter the development and reproduction of aquatic life (Ghiselli and Jardim 2007).
Water resources pose as the final destination of the main pesticides, considering surface and underground resources.Soil and water operate interactively and any action that causes adverse effect in one of these will affect the other.In some cases, less than 0.1% of the amount of applied pesticides reaches the target species while the remaining (99.9%) has the potential to move to other environmental compartments, such as surface water and groundwater through natural processes as leaching, volatilization, degradation, sorption and plant uptake (Ribeiro et al. 2007).
The formulation of the pesticide contains components such as adjuvants and usage modifiers, in addition to the active ingredient.Amongst the adjuvants, there are the surfactants, stickersspreaders, wetting agents, to name but a few.Regarding utility modifiers, there are buffering agents to alter and stabilize solution`s pH and enhance active ingredient solubility; and there are also compatibility agents, to mitigate compatibility problems arising from the mix of multiple pesticides, or pesticides and fertilizers (Fraga 2012).
Surfactants are compounds able to change the surface and interfacial properties of a liquid mixture.They form aggregates, called micelles, usually in low concentrations in solution, decreasing the surface tension of the system and contributing to the stability of the mixture.These compounds are classified into four types, which takes into account the nature of the hydrophilic group: non-ionic, anionic, cationic and amphoteric (Fernandes Providello et al. 2006).After use, residual surfactants are directly released into the sewage system or directly to surface waters, causing pollution of the aquatic system and forming degradation products (Aloui et al. 2009).
Nonylphenol is formed during anaerobic breakdown of the ethoxylated alkylphenols (APEO).In the absence of oxygen, nonylphenol formation is favored (4 to 8 times) when compared to aerobic.Under aerobic conditions, the APEO degrade through either the loss of ethylene oxide units to form low-molecular weight ethoxylates or through the formation of carboxylated ethoxylates ultimately terminating in CO 2 and water.Studies have demonstrated that derivatives of ethoxylated alkylphenols are more persistent and toxic than the parent substances also having the ability to cause disruption of natural hormones to interact with the estrogen's receptor (Renner 1997).It has also been demonstrated (Ahel et al. 1994) that nonylphenol can be degraded by photochemical processes.In bright summer sun, nonylphenol near the water surface has a half-life of 10-15 hr.Another study by Ahel et al. (1996) demonstrated that nonylphenol can be reduced in ground water.The authors suggest that biological processes are responsible provided that the ground water temperature does not become too cold for biological degradation.The authors suggested that this reduction involves biological processes occurring in the part nearest to the river aquifer, provided the groundwater temperature is not low enough for biological degradation (Solé et al. 2000, Zgola-Grześkowiak et al. 2009, Ahel et al. 1994, 1996).
Due to the rapid biodegradation of the alkylphenol ethoxylate, generating more toxic metabolites with potential endocrine disruption, the European Commission, through Directive nº 2003/53/EC banned their use in the European Union.However, the control of the application of these compounds in agriculture is not easy, since many of the products commercially available carry in restricted or no label information about the presence of surfactants in their formulation (Zgola-Grześkowiak et al. 2009).

NATIONAL AND INTERNATIONAL LEGISLATION ON ENDOCRINE DISRUPTERS IN WATER
Over the past few years, a great number of studies trend a growing concern about exposure to chemicals that can interact with the endocrine system and cause adverse effects on wildlife and humans.Studies indicate the presence of these chemicals, called endocrine disruptors in wastewater treatment plants, surface water and groundwater due to the low efficiency of the water treatment process.That is, even after conventional treatment, the water body receptor may still be contaminated (Meyer et al. 1999, Bila et al. 2007).The shortage of water resources is an issue faced by many countries, including Brazil.Highlighting the increasingly imperative need for new studies on the impacts of these disruptors in all beings included in this scenario, studies on water quality among others.
Table I shows the maximum allowed values of some EDs according to the regulation currently enforced both in Brazil and the United States, for surface water and supply as well as the guidance value provided by the Drinking Water Quality Guide World Health Organization Health.Some compounds recently characterized as endocrine disruptors, such as bisphenol a, are not included in the regulations presented in this table.
The guidelines on the quality of US water consumption is given by the Safe Drinking Water Act, establishing the maximum level of contaminants that may be acceptable in drinking water, and the goal of the maximum level of contaminants.Although not enforced as a law, the guide regulates the concentration below which risks to human health are not presented.In addition, another guide is the National Recommendation of Water Quality Criteria (USEPA 2015).FREDERICO G. DE ARAUJO et al.
Brazilian regulation is cosisted of basically two guides: Resolution 357/2005 from CONAMA (National Environmental Agency) (Brasil 2005), for water bodies contamination assessment; and Resolution 2914 from the National Ministry of Health, to stablish and ensure drinkability in public suply.

PHYSICOCHEMICAL PROPERTIES OF NONYLPHENOL
Nonylphenol has a molecular formula C 15 H 24 O (M.M= 220 g mol -1 ).In environmental conditions, it is a viscous liquid, slightly soluble in water (4.90 mg L -1 at 25 °C) and soluble in common organic solvents such as acetonitrile and methanol.It has melting point of -10 °C, boiling point of 304 °C, density of 0.6 g mL -1 at 20 ºC, the vapor pressure of 1.33 Pa (20 °C) and log P in the range of 4.36 to 4.60.In aqueous solution, it behaves as a weak acid with pKa = 10,7.

TOXICITY
After establishing that nonylphenol brings risk to people, the use of its precursor was banned in many countries and replaced by other surfactants, providing more safety for the population and the environment (Soares et al. 2008).
The US Environmental Protection Agency defines an endocrine disrupter compound as "an exogenous agent that interferes with the synthesis, secretion, transport, metabolism, binding or elimination of the body's natural hormones, which are responsible for homeostasis, reproduction, development and / or behavior" (USEPA 1998).
To assess the toxicity of environmental contaminants in aquatic organisms, ecotoxicity tests using algae, bacteria, aquatic invertebrates, zooplankton and fish as test organisms are available.In these tests, not only parameters of toxicity are evaluated, but also biochemical, physiological and behavioral parameters.The acute toxicity of nonylphenol for freshwater animals can vary from 20.7 μg L -1 for the amphipod Hyalella azteca to 774 μg L -1 for snail Physella virgate.At last, chronic toxicity of nonylphenol for freshwater animals ranges from 10.18 μg L -1 for the fish species Pimephales promelas to 157.9 μg L -1 for the crustacean Daphnia magna (USEPA 2005).Azevedo et al. (2001), mentions that the range of concentrations commonly found in rivers is between 0.2 e 12 μg L -1 , values that are already likely to cause problems for some organizations (Azevedo et al. 2001).The efficiency of the extraction process is directly related to the pH of the matrix where nonylphenol is found.The interference of the liquid matrix pH is given by the fact that nonylphenol may have a nonpolar character in the pH range from 0 to approximately 10 and a polar character in pH above 10.7.Consequentially, nonylphenol has greater solubility in the matrix with more alkaline character, because in this pH condition, nonylphenol presents greater ionic character, thereby increasing its water affinity.
In some protocols shown in Table II, there is the inclusion of yet another step, cleaning (cleanup).This step has the purpose of removing any interferences that may have been trapped on the solid phase cartridge and cause problems to the other stages.For this step, it is necessary to select a solvent in which such interferences are soluble (to promote desorption of the solid phase), although the washing solvent must not desorb the analyte.In the analyte desorption step, a great variety of solvents are used, such as methanol (Ciofi et al. 2014, Fabregat-Cabello et al. 2013, Petrovic et al. 2003, Fiedler et al. 2007, Montagner and Jardim 2011, Sodré et al. 2010a), ethyl acetate (Liu et al. 2004), dichloromethane (Martinez and Peñuela 2013), mixture of methanol and water (Cai et al. 2003), acetonitrile and dichloromethane (Azevedo et al. 2001), ethyl acetate and methanol (Souza 2011), dichloromethane and methanol (de Souza Leite et al. 2010, Su et al. 2012), dichloromethane e hexane (Gatidou et al. 2007, Terzopoulou et al. 2014), acidified methanol and dichloromethane (Díaz et al. 2002), methanol andethyl ether (Jeannot et al. 2002), acetone and methanol (Kuch andBallschmiter 2001, Sodré et al. 2010b) and methanol, acetic acid and acetone mixture with dichloromethane (Petrie et al. 2013).
The extraction procedure for solid phase involves two steps: one sorption stage where FREDERICO G. DE ARAUJO et al.   a solid phase presents similar character with the analyte, thereby increasing the value of the partition coefficient.The other step involves the desorption of the analyte, which requires a solvent having high affinity with the analyte to promote the desorption of the solid phase, so that the partition coefficient is the lowest possible.The selection of solid phase and eluting solvent influences considerably the analyte recovery results, as shown in Table I.For nonylphenol, most studies use solid phase hydrophobic character (C18), as the solid phase has a similar character to the analyte (nonpolar), increasing the sorption in phase and causing increased coefficient of analyte solid-phase partition.Regarding elution solvent, it must present characteristics similar to the analyte, thus providing sufficient strength to promote the desorption of the analyte from the solid phase.As a consequence of these two factors, an erroneous choice of solid phase and / or the eluting solvent will cause the extraction procedure to present low recovery values.Regarding solid matrices, there is a scarce number of works to be found, and the predominantly used method of extraction was the ultrasound (Gatidou et al. 2007, Oketola and Fagbemigun 2013, Lara-Martin et al. 2012).It is also observed the use of soxhlet (Jeannot et al. 2002, Bernacka et al. 2009), ultrasound and SPE (Ömeroğlu et al. 2015), PLE (Petrovic et al. 2003) e ASE (Fiedler et al. 2007).In these extraction methods for solid matrices, it is also observed the use of large amounts of sample, reaching 500 g of sample, and exceedingly lengthy protocols.The use of methanol or acetone in the procedures with ultrasound and the use of the extraction using hexane due to the structural similarity with the analyte can also be observed.

ANALYTICAL METHODS FOR THE QUANTIFICATION OF NONYLPHENOL
Given the low polarity of nonylphenol molecule, methods of analysis based on high-performance liquid chromatography (HPLC) and gas chromatography (GC) have been developed.Due to this fact, most investigations reported in the literature refers to these analytical techniques.For most cases, independent of matrix, the use of mass spectrometry (MS) for the detection of nonylphenol is observed, but also observed is the usage of other detectors such as molecular absorption spectrophotometry in ultra-violet (UV) and fluorescence (FLU).
The chromatographic analytical methods for determination of nonylphenol in liquid and solid matrices are shown in Tables III and IV respectively.
As it may be observed in the tables above, the type of matrix and machinery, together with the type of detector, provide a detection limit of quantification and lower values than others.It can be observed in tables III and IV how these factors can greatly interfere with the detection and quantification limit values, causing works that use the same hyphenated techniques to find distinct detection and quantification limit values.Tables 3 and 4, show that in the vast majority of studies published detection limit values and quantification below the maximum level of contaminants recommended by the USEPA as shown in Table I.Thus, demonstrating that the methods already developed and validated by the authors, have great use in environmental monitoring of nonylphenol in liquid and solid matrices.Tables III and IV list the following works which were carried out in Brazil (Azevedo et al. 2001, de Souza Leite et al. 2010, Fiedler et al. 2007, Montagner and Jardim 2011, Sodré et al. 2010a, b).These studies were carried out both in liquid and solid matrices and set quantification limits for liquid samples in the range of ng L -1 to µg L -1 .As for solid samples, the limit of quantification reported by the brazilian authors were in the range of concentration mg kg -1 .

CONCLUSIONS
Nonylphenol has endocrine disrupting capacity and is characteristically prone to accumulating on the environment with high organic matter content.It has low solubility in water, which can cause difficulty in their monitoring in environmental samples.Although there is a significant amount of studies involving determination of nonylphenol in environmental samples, there are few studies in Brazil.The lack of national publications combined with lack of legislation setting nonylphenol limits in Brazil underscores the need to develop analytical methods with analytical reliability for determination of this analyte, and the implementation of monitoring programs to better assess the quality of the environment.

TABLE II
(continuation) FREDERICO G. DE ARAUJO et al.