'Phthalates' is the generic name given to esters of 1,2-benzenedicarboxylic acid. Although some 27 phthalate esters are manufactured, only a limited number are produced in large quantities.

A review by Lewis et al (1998) identified a number of phthalates of particular interest in terms of their environmental fate and behaviour or because they were on the High Production Volume Chemicals List from the EC:

• dimethyl phthalate (DMP);
• diethyl phthalate (DEP);
• two isomers of dibutyl phthalate (DBPs);
• di-iso-butyl phthalate (DIBP) and di-n-butyl phthalate (DNBP);
• butylbenzyl phthalate (BBP);
• dicyclohexyl phthalate (DCHP) and three isomers of dioctyl phthalate (DOP);
• di-n-octyl phthalate (DNOP), di-iso-octyl phthalate (DIOP) and di-2-ethylhexyl phthalate (DEHP)

Phthalates are esters of 1,2-benzoldicarbonic acid (ortho-phthalic acid). The chemical structure of phthalates can be characterised by a planar aromatic ring with two slightly mobile side chains. For phthalates, in general, side chains are mainly alkyl groups with a secondary role played by allyl, benzyl, phenyl, cycloalkyl and alkoxy groups. With alkyl phthalates, a further distinction can be made between branched and unbranched side chains.

In the early 1980s, annual, world-wide production of phthalate esters was estimated to be 20 million tonnes (Schmitzer et al, 1988), although it may now be closer to 5 million tonnes (Lewis et al 1998). The total consumption of phthalate esters in the UK was estimated to be 122,000 tonnes in 1989, of which 54% was DEHP and DIOP (Brooke et al 1991).

Phthalates esters are manufactured world-wide on a large scale, being mainly produced for use as plasticisers in resins and polymers, especially as a softener in PVC (87% of the total production of phthalates is used for this purpose).

Phthalate esters are widely distributed in the environment because of their properties and their common usage as plasticisers. Potential sources by which phthalates may enter the aquatic environment are widely thought to be through:

release via wastewater from production and processing activities, including losses during phthalate ester synthesis, resin and plasticiser compounding, fabrication of PVC into products, and during the production of adhesives and coatings;

release from use and disposal of materials containing phthalate esters, including losses of plasticiser during the lifetime of products or during incineration or landfilling of refuse and other waste.

Phthalates can be considered to be ubiquitous in the environment and there are many studies which have investigated and reported environmental concentrations of these substances. While a few studies have been carried out in the last few years, the majority of available studies are between 10 and 20 years old. Lewis et al (1998) have collated a number of these studies which are summarised below.

It should be noted that contamination during collection and analysis can lead to spurious results and recorded environmental levels where due precautions have not been taken may well be in error.

Data on the concentrations of phthalate esters in environmental samples mainly focus on levels of DEHP, reflecting its predominant usage. Reported levels of DEHP in water samples from rivers in the UK, Sweden, USA and the Netherlands are all within the range 0.3 - 1.6 &micro;g l^-1(Fatoki and Vernon 1990), with levels in coastal, marine and estuarine waters between <2 ng l^-1 and 335 ng l^-1. DOPs are the most hydrophobic of the phthalate esters on the HPVCs List and have been detected in river-bed sediments at concentrations between 0.1 - 1,700 mg kg^-1, depending on whether the samples were collected from clean or contaminated sites. For example, contaminated sediment collected from the Mersey Estuary contained up to 1,700 mg kg^-1 of DEHP (Preston and Al-Omran 1986). It is likely that residues of DOPs accumulating in sediments will persist and that such sediments are a significant sink for those long side-chain or highly branched side-chain phthalate esters.

Sewage sludge is known to contain relatively high concentrations of phthalate esters (12-1,250 mg kg^-1; Shelton et al 1984), the predominant component being DEHP which accumulates on sludge solids because of its hydrophobicity. The disposal of sewage sludge to marine waters was an indirect route of phthalate esters entering the environment, although the discharge of sewage sludge to marine waters is a practise which has been phased out under the Urban Waste Water Treatment Directive (December 1998). The use of sewage sludge as a soil conditioner in agriculture is also a potential indirect route of phthalate esters to the environment (Rogers 1987, Crathorne et al 1989, Fairbanks et al 1985).

Since some phthalate esters have low water solubility and high octanol partition coefficient, they can become concentrated in suspended matter and sediment.

Lewis et al (1998) reviewed data on the fate and behaviour of phthalate esters. The authors concluded that, in general, the substances have low water solubilities and the majority are liquids at ambient temperatures, with melting points below 0^oC, although DMP and DCHP have melting points of 5.5 and 63^oC respectively. Boiling points are 200^OC and above.

The behaviour of phthalate esters in the environment varies, depending on the individual ester. In general, the larger the alkyl side-chain or degree of branching, the more persistent the compound.

The most important aquatic degradation process for phthalate esters is biodegradation. Short side-chain phthalate esters, such as DMP, DEP and DBPs, are all likely to degrade quickly in aerobic surface waters. The longer chain PEs, such as DOPs, are likely to be more persistent, particularly as they will partition more strongly to sediments and so may be less available to microbial degradation. It is, therefore, probable that residues of DOPs in anaerobic sediments will tend to persist for long periods.

Phthalate esters show a wide range of affinities for partitioning to particulate materials in the aquatic environment. Apart from DMP and DEP, all other phthalate esters considered by Lewis et al (1998) show significant partitioning to suspended solids and sediments. The transport of DOPs, DBPs, and BBP in the aquatic environment is strongly influenced by their association with suspended sediments and other detritus, as is their fate during sewage or effluent treatment processes. Log Koc for the phthalate esters increase in the order DMP<DEP<BBP<DNBP<DEHP<DNOP and cover a wide range of hydrophobicities. DMP has the lowest affinity for partitioning to particulate materials and has the highest water solubility. Partitioning tendency increases with side-chain length, with DNOP having the greatest affinity for suspended, particulate material in natural waters. Consequently, the long side-chain phthalate esters that enter the aquatic environment in effluent streams are likely to show significant association with suspended particulate material and sediments or with particulates and sewage sludge during treatment processes. In particular, longer chain phthalates (e.g. DOPs) show a strong affinity for sewage sludge which may reduce the likelihood of high concentrations occurring in the effluent.

Phthalate esters have generally low volatility (vapour pressures in the range 0.02 - 1.9 m Pa) which decrease with increasing length of the alcohol side-chain of the ester. Henry's Law constants range between 10^-8 and 10^-5 atm m³ mol^-1, indicating that phthalate esters will tend to volatilise from water, either not at all or very slowly.

DMP and DEP can be regarded as having low propensity for bioaccumulation, whilst BBP and DBPs have intermediate tendency. DEHP, DCHP, DNOP and DIOP all have a high affinity for sediments or for partitioning to biota.

An exhaustive literature review on the toxicity of phthalates 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 (Lewis et al 1998). The most sensitive groups of organisms have been identified.

The toxicity of phthalates to saltwater organisms varies, depending on the ester considered. Esters, in general, appear to be of moderate to low toxicity to aquatic organisms. However, greatest sensitivity is exhibited when exposed to short side chain phthalate esters, such as DBP and BBP.

For algae, respective EC50 (growth) and LC50 values of 54 and 125 mg l^-1 have been reported for the diatom Gymnodinium breve following 96 hours exposure to DMP (Wilson et al 1978), while 96 hour EC50s of 26.1 and 29.8 mg l^-1 have been reported for Skeletonema costatum on the basis of chlorophyll a and cell number respectively (Suggat and Foote 1981, cited in Staples 1997). For DEP, respective EC50 (growth) and LC50 values of 3 and 33 mg l^-1 have been reported for the diatom Gymnodinium breve following 96 hours exposure (Wilson et al 1978).

For DBPs, the limited available data suggest that saltwater algae are sensitive with 96 hour EC50 (growth) and LC50 values reported for the diatom Gymnodinium breve ranging from 0.0034 - 0.2 and 0.002 - 0.6 mg l^-1 respectively (Wilson et al 1978). However, a single 96 hour EC50 (growth rate) of 31,000 mg l^-1 DEHP has been reported for the alga Gymnodinium breve indicating low acute toxicity.

The available data suggest that DMP is of moderate acute toxicity to crustacean species, with a 96 hour LC50 of 68.6 mg l^-1 reported for the mysid shrimp Mysidopsis bahia following exposure to a measured concentration (Adams et al 1995 and Suggat and Foote 1981, cited in Staples 1997). This value is supported by a 96 hour LC50 of 62 mg l^-1 reported by Linden et al (1979) for the copepod Nitocra spinipes.

DEP also appears to be of moderate acute toxicity to saltwater crustaceans, with a 96 hour LC50 of 10.3 mg l^-1 (measured concentration) reported by Adams et al (1995) for the mysid shrimp Mysidopsis bahia. Of somewhat lower sensitivity is the brine shrimp Artemia salina with a 72 hour LOEC (hatching) of 50 mg l^-1 reported by Sugawara (1974). In this study, a corresponding NOEC of 20 mg l^-1 was reported.

However, greater sensitivity is exhibited by saltwater invertebrates when exposed to DNBP and BBP.

24 hour LC50s of 5.6 and 8.9 mg l^-1 for DNBP have been reported for the brine shrimp Artemia salina exposed to nominal concentrations in two separate studies (Hudson and Bagshaw 1978 and Hudson et al 1981). A lower 96 hour LC50 of 0.5 mg l^-1 has been reported for the mysid shrimp Mysidopsis bahia following exposure to measured concentrations (Adams et al 1995).

For BBP, a 96 hour LC50 of 0.9 mg l^-1 has been reported by Gledhill et al (1980) for the shrimp Mysidopsis bahia with a corresponding NOEC of 0.4 mg l^-1 measured in this study. A further 96 hour NOEC of >0.9 mg l^-1 has been reported in a similar study (Adams et al 1995).

In studies conducted on the copepod Nitocra spinipes and the mysid shrimp Mysidopsis bahia no effects were observed below the maximum water solubility of DEHP. L(E)C50 values for each of these species were reported to be >0.37 and >300 mg l^-1 respectively following 96 hours exposure (Linden et al 1979 and Adams et al 1995).

For saltwater fish, reliable 96 hour LC50s of 0.51, 3 and 0.55 mg l^-1 BBP have been reported for shiner perch Cymatogaster aggregata, sheepshead minnow Cyprinodon variegates and English sole Parophrys vetulus respectively (Ozretich et al 1983; Gledhill et al 1980 and Randell et al 1983).

The limited available data for DMP suggest that it is of moderate acute toxicity to saltwater fish, with 96 hour LC50s of 29 and 58 mg l^-1 reported in two separate studies for the sheepshead minnow Cyprinodon variegates (Adams et al 1995 and Heitmuller et al 1981). However, a lower 96 hour LC50 of 107 mg l^-1 (nominal concentration only) has been reported for the bleak Alburnus alburnus (Linden et al 1979), indicating a possible lower toxicity to this species.

It is difficult to assess the toxicity of DBPs to saltwater fish from the limited data available. In a 96 hour study, no mortality of sheepshead minnow Cyprinodon variegatus was observed at 0.6 mg l^-1, the highest concentration tested (Adams et al 1995). This is supported by the results of a long-term study conducted on the eggs and larvae of a cyprinid Rivulus marmoratus. In this study, 2-4 week NOEC and LOEC values of 1 and 2 mg l^-1 were reported respectively, on the basis of a decrease in egg fertility and embryo viability.

A 96 hour NOEC (survival) of 550 mg l^-1 has been reported for DEHP by Heitmuller et al (1981) for sheepshead minnow Cyprinodon variegatus. However, it is not possible to interpret this value as it is well above the solubility limit of DEHP. Similarly, no mortality was observed in the same species following exposure to the highest concentration tested (0.17 mg l^-1) (Adams et al 1995).

Some information on the toxicity of phthalate esters to sediment dwelling organisms is available. However, these are for freshwater organisms.

Given the low water solubility of DEHP and its high octanol-water partition coefficient, it is likely that this compound will readily adsorb to suspended solids and sediments in the natural environment.

Streufert et al (1980) found that in a flow-through study utilising DEHP concentrations of 0.36 mg l^-1 over sand and 0.24 mg l^-1 over hydrosoil, no effects were observed on the larvae of Chironomus plumosus over a 35 day exposure period. Adsorption of the dissolved fraction to the sand/hydrosoil may have reduced bioavailability and hence toxicity. This observation is supported by the results of the following sediment studies. In a study utilising spiked river sediments, a NOEC of >10,000 mg kg^-1 (survival, development and emergence) was measured for larvae of the midge Chironomus riparius (Brown et al 1996). The authors found that this value was seventeen times greater than the highest concentrations measured in contaminated sediments in the natural environment. These results are supported by the findings of Call et al (1997) who found that spiked sediment concentrations of 3,306 and 3,247 mg kg^-1 (dry weight) caused no adverse effects on survival or growth of the midge Chironomus tentans or scud Hyallela azteca respectively, over a period of 10 days.

In a study conducted by Wennberg et al (1997), a concentration of 600 mg kg^-1 (spiked sediments) was found to cause no adverse effects on hatching success or tadpole survival in the moor frog Rana arvalis over a 29 day period.

Lewis et al (1998) derived EQSs for the protection of saltwater life for a range of phthalate esters (see table below).

Proposed EQSs for the protection of saltwater life for phthalates (&micro;g l^-1) (from Lewis et al 1998)

Bioaccumulation of phthalate esters does not appear to be significant. Wofford et al (1981) exposed the oyster Crassostrea virginica, brown shrimp Pennies aztecus and sheepshead minnow Cyprinodon variegatus to concentrations of 0.1 and 0.5 mg l^-1 (DEHP). Bioaccumulation did not vary significantly among the three species, with reported BCFs ranging from 6.9 (oyster) to 16.6 (shrimp), although exposure was for 1 day only. In longer term studies, Brown and Thompson (1982) recorded an average BCF of 2,496 for mussels (total soft tissues), following 28 days exposure to concentrations of 0.004 and 0.042 mg l^-1. No apparent adverse effects on the mussels were observed, and accumulated residues were rapidly eliminated following transfer to clean seawater (half-life = 3.5 days). It should be noted that, since the BCFs were based on ¹⁴C levels, the values might also include metabolites of DEHP.

Wofford et al (1981) determined BCFs for the brown shrimp Pennies aztecus and sheepshead minnow Cyprinodon variegatus for other phthalate esters, but found them to be low (<50).

Potential effects include:

• toxicity of phthalates at concentrations above the relevant EQSs in the water column;
• accumulation in sediments of long side-chain or highly branched side-chain phthalate esters (e.g. DOPs) posing a significant hazard to sediment dwelling organisms;
• phthalate esters have been identified as a group of substances causing endocrine disruption and a precautionary approach should be adopted in the control of these substances.

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