Microplastics (MP) are defined as plastic particles smaller than 5mm. Microplastics can cause damage to the environment because their small size makes them accessible to a wide range of organisms, resulting in physical and toxicological damage(Law and Thompson 2014). MPs pollution has received worldwide attention due to its abundance and persistence in the aquatic environment, which is increasingly recognized as an environmental threat(Sharma and Chatterjee 2017). PMs can serve as vectors and sources of other environmental contaminants (Alimi et al. 2018). MPs can adsorb and concentrate organic pollutants [e.g., polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs)](Liu et al. 2016; Xu et al. 2019) and heavy metals (such as Cd, Zn and Cu)(Wang et al. 2019a) from the environment, resulting in concentrations thousands of times higher than those in the environment(Hirai et al. 2011). These pollutants are incorporated into the polymer through non-covalent bonds or van der Waals forces, which are quickly released into the environment, especially during plastic fragmentation(Lithner et al. 2011).
Polyethylene (PE) and polypropylene (PP) MPs are widely present in environments and are among the most used plastics around the world(Li et al. 2019). A study by Huang and co-workers investigated the abundance of microplastics in agricultural soils across China, suggesting that plastics are closely related to the accumulation of microplastics in arable land(Huang et al. 2020). PE and PP are among the MPs detected in the Rhine River sediments, about 49% and 26%, respectively(Klein et al. 2015). In agricultural soils in Germany, PE and PP MPs have been detected in roughly 62.5% and 25%, respectively(Scheurer and Bigalke 2018). A study on the coast of Guangdong, South China, showed that PE and PP are present in about 25% and 21% of the total microplastic fragments(Fok et al. 2017). A survey conducted by Olivatto and co-workers revealed that MPs contamination in Guanabara Bay, Rio de Janeiro, Brazil, consists of 81.7% of PE and 16.2% of PP(Olivatto et al. 2019).
It is well established that MPs can adsorb polluting molecules, thus serving as carriers for these molecules(Yang et al. 2019). Aquatic organisms can ingest MPs with pollutants, causing damage to their health(Fu et al. 2021). It is estimated that, on average, about 0.1–5.0g of MPs are consumed weekly by humans through various exposure pathways(Senathirajah et al. 2021). Adsorption of multiple pollutants onto typical microplastics (PE and PP) has been investigated, such as heavy metals, dyes, pesticides, pharmaceuticals, and antibiotics(Li et al. 2021; McDougall et al. 2022).
No matter how these pollutants coexist with MPs, MPs can transfer them to organisms and promote their bioaccumulation and toxicity(Zhao et al. 2020). Butylated hydroxyanisole (BHA) is a synthetic phenolic antioxidant (SPA) widely used in plastics(Rodil et al. 2012). BHA is a mixture of two isomers [2-tertiary-butyl-4-hydroxyanisole (2BHA) and 3-tertiary-butyl-4-hydroxyanisole (3BHA)] where the 3BHA is the major isomer(Berridge et al. 1984). Although these isomers have similar oxidation potentials, 3BHA has a 2 to 4 times greater antioxidant activity than 2BHA(Akaranta and Odozi 1986). Furthermore, 3BHA represents 90% of the commercial BHA(Pop et al. 2013).
BHA has been detected in various environmental samples such as surface water, sewage effluent, municipal sewage sludge, house dust(Wang et al. 2018), and in humans in urine and serum samples(Wang et al. 2019b). BHA has endocrine-disrupting properties that can disrupt estrogen secretion and steroid hormone homeostasis(Yang et al. 2018). Zhao and co-workers(Zhao et al. 2020) found that MPs promoted BHA accumulation in zebrafish larvae, increased BHA toxicity in larval development due to reduced hatching rates, increased malformation rates, and decreased calcified vertebrae. The use of zebrafish larvae (Danio rerio) as a vertebrate model has frequently been used to study the toxicity of environmental contaminants(McCollum et al. 2011).
The main objective of this work is to elucidate the adsorption mechanism of 3BHA on PE and PP MPs through molecular dynamics (MD), density functional theory (DFT), non-covalent interactions (NCI), density of states (DOS) and frontier molecular orbital (FMO). Unraveling the 3BHA adsorption mechanism on PE and PP MPs will provide in-depth knowledge about your ecological and environmental risk.