Naphthalene is a polyaromatic hydrocarbon (PAH) with two benzene rings.

A number of reviews on the potential environmental impact of naphthalene have been published, including reports by the United States Environmental Protection Agency (US EPA 1980) and the Commission of the European Communities (Masoero et al. 1985); the Building Research Establishment (BRE) (Gavin et al. 1996) as have EQSs for the protection of aquatic life (Bates et al 1997).

Naphthalene is a non-polar PAH which occurs naturally as a component of coal tar and crude oil and is manufactured for use principally as a chemical intermediate (e.g. phthalic anhydride). It may be found in a wide range of products, including petroleum products, mothballs, wood preservatives, solvents and dyes, and can be released to the aquatic environment by a variety of means (e.g. discharges or spillages from the chemical and petroleum industries, coal gasification plants, atmospheric fallout). The main source of naphthalene in the environment is believed to be vehicle exhaust (naphthalene is a combustion product of motor fuel) (Gavin et al. 1996).

In 1995, the Environment Agency routinely monitored the levels of naphthalene in English and Welsh freshwater, saltwater and groundwater systems. Annual average concentrations of 111.9, 429.7 and 329.3 ng l^-1 respectively, were recorded.

A survey carried out by the Ministry of Agriculture Fisheries and Food (MAFF) in 1993 (and more recently reported in 1998 - see Appendix D) found low levels of PAHs, including naphthalene, in estuaries relatively unaffected by industry or urbanisation. For example, in the Tweed estuary, naphthalene was detected but at a concentration below the limits of detection (<15 ng l^-1). The highest concentrations were found in the industrialised Tees and Thames estuaries, with up to 17,300 ng l^-1 (maximum concentration) occurring in the lower Tees at the Redcar. The high levels recorded in Redcar samples were explained by their proximity to an effluent outfall from a steel works, while the contamination of the Thames estuary was attributed to deposition of PAHs from combustion sources in London. The explanation given for low levels of naphthalene and other PAHs in the Outer Mersey was that PAH pollution is largely carried inland by prevailing winds. In an earlier report, Readman (1982) determined an average naphthalene concentration of 13.9 ng l^-1 in water and 245 &micro;g kg^-1 (dry weight) in sediment from the Tamar estuary near Plymouth.

When released to the environment, the majority of naphthalene is expected to be released to the air (half-lives in air are generally a few hours). Naphthalene is moderately soluble in water and only moderately adsorbs to soil, sediment or suspended solids. In water volatilisation, adsorption, photolysis and aerobic biodegradation may be important fate processes, depending on local conditions. The half-lives for naphthalene in soil and water range from a few days to a few months (Bates et al 1997).

Examination of the reported octanol-water partition coefficients (log Kow 3.01-3.45) suggests that naphthalene is moderately hydrophobic and may thus have a tendency to adsorb to particulate matter (e.g. soil and sediment particles) and accumulate in biota (Bates et al 1997).

Contamination of the aquatic environment with naphthalene is most frequently associated with discharges from the chemical and petroleum industries and accidental spillages or leakages of petroleum products to land or water.

An exhaustive literature review on the toxicity of naphthalene to marine organisms has not been carried out for the purposes of this profile. The information provided in this section is taken from existing review documents (Bates et al 1997). The most sensitive groups of organisms have been identified.

Bates et al (1997) have reviewed data on the toxicity of naphthalene to saltwater species. The authors found the information to be mostly limited to the results of single-species, acute laboratory tests. The majority of toxicity studies reported in the literature tested the effects of concentrations well below the solubility limit (20 mg l^-1 in seawater) and usually, measures have been taken to minimise losses of naphthalene from the test system due to volatilisation, often with analytical confirmation of exposure concentrations.

Examination of the available toxicity data indicates that naphthalene is of high to moderate acute toxicity to saltwater life, with the majority of effect concentrations ranging from 0.4 to 5 mg l^-1. Limited data are available on the effects of chronic naphthalene exposure. However, significant reductions in the reproduction of estuarine copepods have been recorded after chronic exposure to concentrations as low as 0.01 mg l^-1 and histopathological and physiological damage have been observed in fish Fundulus heteroclitus after sub-chronic exposure to 0.02 mg l^-1.

No major taxonomic group appears to be significantly more sensitive to naphthalene than any other, although acute effects have been observed for molluscs, crustaceans and fish at concentrations below 1 mg l^-1.

Bates et al (1997) found only one study which investigated the accumulation of naphthalene by saltwater annelids. Arenicola marina was exposed to ¹⁴C-1-naphthalene via water and sediment and found that the uptake of naphthalene was more rapid when worms were exposed to water only. Accumulation factors of approximately 300 and 160 were reported for the stomach wall and oesophageal glands (the major sites of accumulation) respectively, when worms were exposed to naphthalene dissolved in water. However, almost complete depuration of the accumulated naphthalene was observed after 24 hours. When worms were exposed to labelled naphthalene in sediment, the accumulation factors reported for the stomach wall and oesophageal glands were 4.075 and 0.69 respectively, which indicated that naphthalene adsorbed to sediment was much less bioavailable than dissolved naphthalene.

The bioaccumulation of naphthalene from sediment was investigated for the baltic clam Macoma balthica in a laboratory flow-through system. Estuarine sediment was fortified with naphthalene-d₈ and added to filtered seawater (salinity 12.7l) to give a nominal concentration of 15 &micro;g g^-1 organic carbon (1.36% organic carbon). The study results suggest that sediment may be an important source of exposure to benthic estuarine organisms, such as clams.

Environment Canada has recently issued interim marine sediment guidelines (see Section 5.5) and these include a guideline for naphthalene of 34.6 &micro;g kg^-1 (dry weight), above which effects on sediment-dwelling organisms may occur.

Naphthalene may accumulate significantly in aquatic biota, with the majority of BCFs between 50 and 400. However, there is evidence of metabolism and rapid depuration by invertebrates and fish. When returned to uncontaminated water, naphthalene has been shown to depurate rapidly from both fresh and saltwater invertebrates and fish (from 24 hours to a few weeks, depending on the species, life-stage and exposure concentration) (Bates et al 1997).

Potential effects include:

• toxicity of naphthalene to invertebrates and fish at concentrations above the EQS of 5 &micro;g l^-1 (annual average) and 80 &micro;g l^-1 (maximum allowable concentration) in the water column;
• accumulation in sediments and potential hazard to sediment dwelling organisms at concentrations greater than 34.6 &micro;g kg^-1 (dry weight);
• bioaccumulation of naphthalene in aquatic biota.

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