Review of Environmental Fate and Effects of Selected
Phthalate Esters

2 Summary and conclusions

2.1 Concentrations in the environment
2.2 Degradation
2.3 Bioaccumulation
2.4 Toxicity
2.5 Estrogenic effects
2.6 Environmental Hazard Classification
2.7 Predicted No-Effect-Concentrations for the aquatic environment
2.8 Summary of the environmental fate and effect of 6 phthalate esters
 

2.1 Concentrations in the environment

The quality of chemical analysis of phthalates in environmental samples has been under debate during recent years. One of the main problems is the common use of plastic equipment in laboratories often containing platicizers. Consequently, the samples to be analysed may be contaminated during sampling, storage, processing as well as during analysis if a proper methodology has not been implemented. Thus, many of the results reported - especially in older references - may overestimate the concentrations in the samples due to contamination. This can be illustrated by measurements of e.g. DBP in rivers, in which the measured concentrations vary from 0.001 to 622.9 µg/l.

2.2 Degradation

Phthalate esters can undergo hydrolysis in two steps under production of mono-ester and a free alcohol in the first step and phthalic acid and a free alcohol in the second step. Hydrolysis, however, seems to play only an insignificant role for the degradation under natural environmental conditions with increasing hydrolysis rates at increasing pH /1, 2, 3/.

Photodegradation may be an important degradation pathway in atmosphere with predicted half-lives in the range of a few days /4/. However, in the soil and aquatic environments, the light intensity is so low that no significant photodegradation can be expected /1/.

In general, phthalate esters with short alkyl chain length are readily biodegradable but the mineralization rate decreases with increasing ester chain length.

Because of the ubiquitous use of phthalates, many sewage treatment plants contain adapted micro-organisms capable of degrading these substances. Also in anaerobic sewage sludge digesters, a potential for mineralization of some phthalate esters may be expected. Exceptions to this degradation behaviour may be the long-chain length phthalates, and only few data are available on the degradation of these substances under anaerobic conditions. However, relatively high amounts of long-chain length phthalates are found in sewage sludge demonstrating a low biodegradability under normal conditions in sewage treatment plants.

In tests performed at environmentally relevant conditions, mineralization of the short-chain phthalate esters has been found. The degradation of longer chain phthalate esters is lower and often only a primary biodegradation is found. Moreover, especially at low temperatures, the degradation is considerably slower than determined at the standardised laboratory conditions.

2.3 Bioaccumulation

In general, phthalate esters should be expected to be bioaccumulative due to their log K_ow values ranging from 1.61 (DMP) to >8 (DINP, DIDP). However, the accumulation is influenced by the capability of an organism to metabolize the substances. Numerous experiments have shown that bioaccumulation of phthalate esters in the aquatic and terrestrial food chains is limited due to biotransformation. The metabolic capability increases with increasing trophic levels.

Phthalate ester metabolism appears to depend upon both species and exposure route. Results indicate that mean BCFs are highest for algae and lowest for fish with invertebrates exhibiting intermediate values /1/. These findings are consistent with previous studies by Wofford et al. (1981) /5/ who found that the extent of phthalate ester biotransformation increased as follows: molluscs < crustaceans < fish.

2.4 Toxicity

Detailed studies of the mode of toxic action of phthalate esters in aquatic organisms are lacking, however, polar narcosis is generally accepted as being the primary mode of action.

The low water solubility of some phthalate esters causes problems when exposing aquatic organisms in toxicity tests. The formation of micro droplets, surface films and adsorption to surfaces lead to difficulties in maintaining steady exposure concentrations and/or cause direct physical interference. The low water solubility has led to the widespread use of carrier solvents in toxicity testing. Reported aqueous effect concentrations often greatly exceeds true water solubilities in tests performed with higher molecular weight phthalate esters. Water solubility, biodegradation, and sorption may thus significantly influence the results of these aquatic toxicity tests.

When test solutions are prepared in concentrations higher than 'true' water solubility of the phthalate esters, an emulsion of microdroplets consisting of pure chemical may be formed. The formation of microdroplets or surface films may contribute to possible effects by direct physical interference.

Small colloids may increase the apparent water solubility by sorbing lipophilic substances. They may, however, either decrease or increase the bioavailability and thus the toxicity. For most substances, the presence of particulates and colloids probably decreases the bioavailability, but for certain types of organisms (especially suspension feeders and detritovores) the reverse effect might be the case.

When interpreting toxicity data on sparingly soluble substances such as especially the higher molecular weight phthalate esters (DINP and DIDP), it is very important that the above parameters are taken into account.

2.5 Estrogenic effects

The potential for estrogenic effects in wildlife has been evaluated by means of extrapolation from in vitro and in vivo studies with rats. Lack of in vivo studies for phthalate esters in aquatic environments makes assessment of their potential estrogenic effects in aquatic wildlife difficult.

2.6 Environmental Hazard Classification

The phthalate esters have not been considered for environmental hazard classification by the EU "Labelling Group". However, based on the present review of the environmental fate and effects of the phthalate esters, classification proposals have been derived.

The main parameters to be considered for the environmental hazard classification (EEC 1993) are:

• acute toxicity to algae, daphnia and fish
• chronic toxicity to daphnia and fish
• ready biodegradability
• bioaccumulation potential (log K_ow or experimentally derived BCF)
• water solubility

2.7 Predicted No-Effect-Concentrations for the aquatic environment

Predicted No Effect Concentrations (PNEC_aquatic) have been derived for the phthalate esters evaluated. When possible, the PNEC values were derived from long-term studies on algae, crustaceans and fish. As, however, only short-term studies exist for one of the phthalate esters evaluated, PNEC have been derived from these. For DINP and DIDP, no PNEC_aquatic could be derived.

2.8 Summary of the environmental fate and effect of 6 phthalate esters

The fate and effect of Dimethyl Phthalate (DMP); Diethyl Phthalate (DEP); Di-n-butyl Phthalate (DBP); Butylbenzyl Phthalate (BBP); Diisononyl Phthalate (DINP) and Diisodecyl Phthalate (DIDP) have been summarized in Table 2.1.

Table 2.1
link to table