Combined effects of pH and dissolved organic matter on the availability of pharmaceuticals and personal care products in aqueous environment.

The interaction between pharmaceuticals and personal care products (PPCPs) with dissolved organic matter (DOM) can alter their bioavailability and toxicity. Nevertheless, little is known about how pH and DOM work together to affect the availability of PPCPs. This study investigated the impact of pH and DOM on the availability of seven PPCPs, namely Carbamazepine, Estrone, Bisphenol A, Testosterone Propionate, Triclocarban, 4-tert-Octylphenol and 4-n-Nonylphenol, using negligible depletion solid-phase microextraction (nd-SPME). The uptake kinetics of PPCPs by the nd-SPME fibers increased proportionally with DOM concentrations, likely due to enhanced diffusive conductivity in the unstirred water layer. At neutral pH, the partitioning coefficients of PPCPs for Humic Acid (log KDOC 3.87-5.25) were marginally higher than those for Fulvic Acid (log KDOC 3.64-5.11). Also, the log KDOC values correlated linearly with the log DOW (pH 7.0) values of PPCPs, indicating a predominant role for hydrophobic interactions in the binding of DOM and PPCPs. Additionally, specific interactions like hydrogen bonding, π-π, and electrostatic interactions occur for certain compounds, influenced by the polarity and spatial conformation of the compounds. For these ionizable PPCPs, the log DDOC values exhibit a strong dependence on pH due to the dual influence of pH on both DOM and PPCPs. The log DDOC values rose from pH 1.0 to 3.0, peaked at pH 5.0 to 9.0, and then (sharply) declined from 11.0 to 13.0. The reasons are that in strong acidic circumstances, the coiled and compressed shape of DOM inhibits the hydrophobic interaction, whereas in strong alkaline conditions, significant electrostatic repulsion reduces the sorption. This study reveals that the effects of DOM on the bioavailability of PPCPs are dependent on both pH and the specific compound involved.

Effects of nanoplastics and microplastics on the availability of pharmaceuticals and personal care products in aqueous environment.

Nanoplastics (NPs) and microplastics (MPs) could act as potential carriers for pharmaceuticals and personal care products (PPCPs) and alter the bioavailability in the aquatic environment. The effects of NPs and MPs of polystyrene (PS) and polyethylene (PE) on the availability of five PPCPs including carbamazepine, bisphenol A, estrone, triclocarban and 4-tert-octylphenol were investigated by negligible depletion solid- phase microextraction (nd-SPME). The freely dissolved concentrations of PPCPs decreased with the increasing concentrations of NPs/MPs. The overall order of the sorption coefficients (logKNP / logKMP) of PPCPs was as follows: 100 nm PS > 50 nm PS > 1 µm PS > 100 µm PS > 100 µm PE. Sorption of PPCPs by NPs was generally 1-2 orders of magnitude stronger than to MPs. The log KNP / log KMP values (3.16-5.21) increased with the log KOW (2.45-5.28) of PPCPs, however, linear correlation was only observed between log KMP and log KOW. The particle size, specific surface area, aggregation state as well as hydrophobicity played an important role in the sorption. Coexistence of fulic acid (FA) with NPs inhibited the sorption due to the fouling of FA on NPs. This study suggests that sorption of PPCPs to MPs/NPs could reduce bioavailability of PPCPs in the aquatic environment.

Evaluating the effect of different modified microplastics on the availability of polycyclic aromatic hydrocarbons.

Microplastics (MPs) discharged into the natural environment undergo various wearthering pathways, such as mechanical abrasion and ultraviolet (UV) irradiation. However, little is known about the effects of such aged MPs on the bioavailability of hydrophobic organic compounds (HOCs) in aqueous environments. To simulate the natural oxidation and UV-ageing process of MPs, three kinds of modified polyethylene MPs were obtained by plastic etching processes common in industry and UV irradiation, namely, etched MPs (EMPs), UV-aged MPs (UV-MPs), and etched MPs followed by UV ageing (UV-EMPs). The modified MPs showed a higher content of surface oxygen-containing groups than the pristine MPs, and the specific surface area and pore volume increased significantly after etching and ultraviolet ageing, especially for the EMPs (1.67 m2 g-1 and 0.0049 cm³ g-1) and UV-EMPs (2.37 m2 g-1 and 0.0089 cm³ g-1). The effect of modified MPs on the availability of 10 polycyclic aromatic hydrocarbons (PAHs, logKow 4.18-6.20) was evaluated by negligible-depletion solid-phase microextraction (nd-SPME). The free concentrations (Cfree) of most PAHs (except for less hydrophobic PAHs, logKow 4.18 and 4.56) decreased with an increasing concentration of MPs. The logarithms of the sorption coefficients of PAHs with various MPs (logKMPs, logKUV-MPs, logKEMPs and logKUV-EMPs) were linearly correlated with logKow, suggesting that the sorption is hydrophobicity dependent. Compared with the results for pristine MPs (logKMP 3.80-4.95), UV ageing only slightly enhanced the sorption of PAHs by MPs (logKUV-MPs 3.71-4.98), whereas the plastic etching processes significantly enhanced sorption (logKEMPs 3.85-5.18 and logKUV-EMPs 3.90-5.28). The sorption of PAHs to MPs is mainly based on partitioning; however, a mechanism of adsorption also likely takes place in EMPs and UV-EMPs due to hydrogen bonding and π-π interactions. Desorption study indicated that PAH desorption from MPs are dominated by film diffusion. However, intraparticle diffusion also takes great part for the EMPs. These results suggest that modification of MPs in the natural environment will change the availability of HOCs.