## 2 Physical, Chemical, and Environmental Properties of Phthalates  
Phthalates are formed by a reaction of phthalic anhydride with various alcohols. The number of carbon atoms present will determine the length of the lateral chains R and R', and thus, the molecular weight of the phthalate is obtained [1]. PAEs differ chemically in the substitutions of the R1 and R2 side chains (which characterise their physicochemical properties) and are slightly volatile liquids, generally colourless, odourless, and oily liquidsat room temperature [6]. In addition, their solubility in fat (lipophilic property) increases with the lengthening of the side chains R and R\({}^{\prime}\) (Figure 1). Although there is no unique classification, it is generally possible to distinguish low molecular weight PAEs (LMW PAEs) with 3-6 carbon atoms in their side chain, and high molecular weight PAEs (HMW PAEs) with R and R\({}^{\prime}\) from 7 to 13 carbons [1]. LMW PAEs include DMP, diethyl phthalate (DEP), DnBP, DiBP, and dimethylglycol phthalate (DMEP) and are typically used in PVC products, medical devices, personal care products, cosmetics, adhesives, paints, printing inks, pesticides, toys, enteric-coated tablets, food packaging or bag, etc. Most of the common phthalates are reported in Table 1.  
PAEs with shorter alkyl chains, such as DMP and DEP, are widely used as solvents and fixatives, allowing fragrances, for example, to evaporate more slowly and to persist, thus extending product life [1; 2; 19]. HMW PAEs include BBzP, DEHP, DnOP, DiNP and DIDP, and dipropyl heptyl phthalate (DPHP), which are most commonly used as plasticisers to provide the plastic vinyl its flexibility [1]. PAEs have a relatively high boiling point and low melting point, which confers properties particularly suitable for use as plasticisers, heat transfer fluids, and carriers in the polymer industry [1]. Linear esters offer superior flexibility at low temperatures and have lower volatility than branched esters [1]. As a result of these characteristics, PAEs are widely used both as plasticisers and also as non-plasticising agents [20] in large quantities. In fact, some products may consist, by weight, of up to 40% of phthalates [21]. Despite their favourable physicochemical properties and their versatility of application in several fields that have provided numerous benefits to society, PAEs have instead demonstrated several adverse health effects of exposed organisms in all environments, especially in aquatic ones [22]. Since phthalates are not chemically bound to the polymers in which they are mixed, they can be released (for example, by contact, leaching, migration, or evaporation) in the environment, leading to exposure to the organisms present therein [22; 23; 24]. PAE residues have been detected in all environmental compartments. Extensive production, the storage of waste containing PAE in the environment, the inefficiency of traditional waste plants on the complete degradation, and the possible negative effects of PAEs on human health pose great global environmental and health risks for long durations [25]. Different reservoirs depend on different physicochemical properties, including water solubility (S\({}_{w}\)), vapour pressure (V\({}_{p}\)), Henry's constant (K\({}_{H}\)), air/water partitioning, octanol/air partitioning (K\({}_{\alpha\alpha}\)), octanol/water partitioning (K\({}_{\omega\omega}\)), organic carbon partitioning (K\({}_{\infty}\)), and abiotic degradation/biodegradation processes [1]. Figure 1: General chemical structure of phthalate esters. In the aquatic environment, among all the possible sources of contamination, certainly, the impact of plastics (a major source of contamination) in different environmental matrices has contributed and is contributing to their ubiquitous diffusion (due to their ability to float and resist degradation). Phthalates, favoured by the size of micro- and nano-plastics, can easily pass from low trophic levels of the food chain such as plankton and fish and then up to top predators and humans [26].