Phthalates

W J G M Peijnenburg, RIVM - Laboratory for Ecological Risk Assessment, Bilthoven, The Netherlands © 2008 Elsevier B.V. All rights reserved.

Introduction Adverse Effects of Phthalates

Emission of Phthalates in the Environment Further Reading

Environmental Fate of Phthalates

Introduction

Phthalates are the esters of 1,2-dibenzene dicarboxylic acid; their general structure is given in Figure 1. They are produced by the addition of an excess of branched or normal alcohols to phthalic anhydride in the presence of a catalyst. Phthalates constitute a diverse family of industrial compounds that are by far the most widely produced plasticizers up to date to increase the flexibility and workability of high molecular weight polymers. Their low melting point and high boiling point make them also very useful as heat-transfer fluids and carriers. In some plastics, phthalates comprise up to 50% of the total weight. Both linear and branched phthalate esters are used in the manufacture of plastics; especially, linear esters provide superior flexibility at low temperatures and also have lower volatility. Phthalates with alkyl side chains lower than C6 are not often used as plasticizers because of volatility concerns. Phthalates can be found in ink, paint, adhesives, vinyl flooring, and even in some food products, cosmetics, and pharmaceuticals.

Exact numbers are lacking, but the estimated worldwide production is about 4 300 000 t yr" , of which c. 90% are used as plasticizers. The C8-C13 phthalate esters are the dominant vinyl plasticizers with di-2-ethyl hexyl phthalate (DEHP) and diisononyl phthalate (DINP) predominant. Currently, however, there is a clear trend of using technical mixtures of alcohols of similar boiling point as precursors, as a matter of course yielding a complex mixture of phthalate esters. Of the dozens of phthalates synthesized over the years, the most prolifi-cally used in Western Europe are DEHP, diisodecyl phthalate (DIDP), DINP, and di-^-butyl phthalate

Figure 1 General chemical structure of phthalates. R1 and R2 = C„H2n+1; n = 4-15.

Other phthalates

DEHP 51%

Figure 2 Approximation of the relative importance of the consumption of four of the main phthalates in the European Union in the 1990s.

(DBP), in this order (Figure 2). Most of the data generated on phthalates are derived from research on these four particular phthalates. It should be noted that DOP (dioc-tyl phthalate) is used as a synonym for DEHP.

Incorporating phthalate esters into a polymeric matrix reduces the glass transition temperature of the polymer. Phthalate esters are not chemically bound (covalent bonds) to the polymer and are therefore able to migrate to the surface of the polymer matrix. Here they may be lost by a variety of physical processes, albeit that various attractive forces hold the esters tightly within the vinyl matrix, so that migration occurs at a low rate. Nevertheless, concern has risen in the European Union on possible adverse effects on infants and consequently they are banned for use in toys.

Emission of Phthalates in the Environment

Phthalates can enter the environment through losses during manufacturing processes by air emissions, in water effluent, in solid waste, and by leaching from final products, because they are not chemically bonded to the polymeric matrix. Very little is released during manufacturing and processing as most of the phthalates released during production and processing are disposed of in waste

DINP 11%

DINP 11%

Figure 2 Approximation of the relative importance of the consumption of four of the main phthalates in the European Union in the 1990s.

DIDP

DIDP

water and are either biodegraded or adsorbed to sludge. The major part of the phthalates found in the environment originates from the migration from plastic matter during use and disposal, also called weathering. The migration capacity varies in an inverse way to their molecular weight. As phthalates are not covalently bound in plastic matrices, they will migrate especially under conditions of high surface exposure and warm temperatures. This is especially so in case of exterior building materials, where phthalate esters can diffuse to air despite their rather low vapor pressure. Diffuse and pinpoint sources thus contribute to their dispersal, mainly from direct wet and dry atmospheric deposition, via surface water, and via indirect runoff and overland flow. As river inputs contribute to oceanic pollution, the Oslo and Paris Convention (OSPAR) for protection of the marine environment in the North-East Atlantic included DBP and DEHP on the list of priority chemicals of concern. In spite of bacterial degradation in surface water and degradation by photolysis, phthalates are at the present time detected in different compartments of the environment at concentrations ranging from 0.3 to 77 ngm-3 in the atmosphere, from 0.3 to 98 mgl_1 in surface water, from 0.2 to 8.4 mg per kg dry weight (DW) in sediment, and from 28 to 154 mg per kg DW in sewage sludge, albeit that at specific spots even higher levels may be found. The highest levels of dissolved DBP and DEHP are found in freshwater samples, whereas these compounds are usually below the limit of detection in marine water and sediment. Median levels are log-normal distributed, and usually the season in which the samples are taken is not a relevant determinant parameter. DEHP levels in pristine waters are generally found to be c. 0.01 mgl_1 in surface water.

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