8 2.3 Chemical ingredients and additives PS foams are complex compounds and are often produced with a variety of chemicals. These chemicals include base ingredients (benzene, styrene), additives (UV stabilizers, dyes, flame retardants), and chemical intermediates. While PS foam usually includes a suite of these chemicals, each individual product is unique. Some common ingredients and additives in PS foam are outlined below, however, precise lists of additives are not easily obtained (regarded as proprietary information). Over time, these ingredients and additives can leach out and often these leachates can act as toxic or endocrine disrupting chemicals in the environment (Hermabessiere et al., 2017). For more on chemical fate and effects, see Section 3. The list below does not represent a comprehensive list, although this section aims to outline the main substances used as monomers, additives, intermediates and catalysts in PS foam production. Benzene – Styrene The main component of PS foam is PS, which is made from a polymerisation process with benzene, styrene, and ethylene (see Section 2.1). Leachates from benzene, styrene and ethylbenzene are one of the reasons why there is often greater concern over PS compared to other plastic types, since these leachates have known toxicity (Thaysen et al., 2018). Benzene is used mainly as an intermediate to make other chemicals. Over half of all benzene production is processed into ethylbenzene (a precursor to styrene). Benzene is also an additive in gasoline (U.S. Environmental Protection Agency, 2006). Styrene evaporates easily and has a sweet smell when aerosolized and styrene fumes are a known irritant (ATSDR, 2010). Under certain conditions, EPS has shown to leach styrene, benzene, and ethylbenzene, chemicals with toxic effects (ATSDR, 2010; Gibbs and Mulligan, 1997; Thaysen et al., 2018) Additives Hahladakis et al. (2018) reported on a comprehensive list of chemical substances known as “additives” contained in plastics for enhancing polymer properties and prolonging their life. PS is slightly brittle, and additives are often incorporated into PS to achieve strength and durability. Since PS foam is used in a range of different products, chemical additives included depend on the end use (Smith and Taylor 2002). Common PS additives include antioxidants, UV stabilizers, lubricants, colour pigments, nucleating agents, and flame retardants (Smith and Taylor 2002). This complex mixture can vary depending on the manufacturer and end use. For example, some EPS panels used in construction for thermal and sound insulation are made up of 91-94% PS, 2-7% pentane, < 1% fire protection agent, and small amounts of PE waxes, paraffin, and other additives (Ibo Osterreichisches Institut Fur Baubiologie Und-Okologie, 2016). Some EPS and XPS blocks used in dock construction have a thin surface layer finish to give increased protection from UV degradation and physical abrasion (Dunham and Finn, 1974). Antioxidants and UV stabilizers are commonly added to plastics to prevent oxidation and degradation (Tikuisis and Dang, 1998). When plastics are exposed to ultraviolet (UV) light, it can lead to oxidative degradation in polymers (Hahladakis et al., 2018). UV stabilizers prevent this type of degradation, which is often a “yellowing” reaction observed in PS (Andrady and Pegram, 1991). While the chemical reactions causing this reaction are poorly understood, the mechanism of yellowing is likely due to a variety of chromophores, which lead to discoloration (Andrady and Pegram, 1991). Antioxidants and UV stabilizers often markedly slow light-induced degradation of plastic, including PS. Lubricants enhance polymers with antistatic and anti-stick properties. Some of the most common compounds are fatty acid amides, which can also be used as emulsifiers in the polymerization processes (Ašmonaitė et al., 2018). Some lubricants are external, while others are internal to the plastic (Lau andWong, 2000). Leachate A leachate is a liquid that extracts soluble compounds or suspended solids when it passes through a material. For example, under certain conditions, when polystyrene is exposed to water, it can leach chemicals (i.e. styrene), and the result is a leachate containing water, styrene, and other chemicals.