Interactions between microplastics and phthalate esters as affected by microplastics characteristics and solution chemistry.

Microplastics have become a major concern in recent years as they can be recognized as the transport vectors for pollutants in environment. In this study, the sorption behavior of two phthalate esters (PAEs), including diethyl phthalate (DEP) and dibutyl phthalate (DBP), onto three types of microplastics (PVC: polyvinyl chloride, PE: polyethylene, and PS: polystyrene) was investigated. The sorption isotherms of both DEP and DBP on microplastics were highly linear, suggesting that the partition was the main sorption mechanism. The Kd values of DBP were much higher than those of DEP, demonstrating that hydrophobic interaction governed the partition mechanism. Sorption of the two PAEs on the three microplastics followed the order of PS > PE > PVC, indicating that chemical properties of microplastics played an important roles in their sorption behaviors. Solution pH and natural organic matter had no significant impact on PAEs sorption by microplastics. However, the presence of NaCl and CaCl2 enhanced the sorption of both DEP and DBP because of the salting-out effect. The findings of the present study may have significant implications for the fate and transport assessment of both PAEs and microplastics.

Joint toxicity of microplastics with triclosan to marine microalgae Skeletonema costatum.

Toxicity of single microplastics on organisms has been reported widely, however, their joint toxicity with other contaminants on phytoplankton is rarely investigated. Here, we studied the toxicity of triclosan (TCS) with four kinds of microplastics namely polyethylene (PE, 74 µm), polystyrene (PS, 74 µm), polyvinyl chloride (PVC, 74 µm), and PVC800 (1 µm) on microalgae Skeletonema costatum. Both growth inhibition and oxidative stress including superoxide dismutase (SOD) and malondialdehyde (MDA) were determined. We found that TCS had obvious inhibition effect on microalgae growth within the test concentrations, and single microplastics also had significant inhibition effect which followed the order of PVC800 > PVC > PS > PE. However, the joint toxicity of PVC and PVC800 in combination with TCS decreased more than that of PE and PS. The higher adsorption capacity of TCS on PVC and PVC800 was one possible reason for the greater reduction of their toxicity. The joint toxicity of PVC800 was still most significant (PE < PVC < PS < PVC800) because of the minimum particle size. According to the independent action model, the joint toxicity systems were all antagonism. Moreover, the reduction of SOD was higher than MDA which revealed that the physical damage was more serious than intracellular damage. SEM images revealed that the aggregation of microplastics and physical damage on algae was obvious. Collectively, the present research provides evidences that the existence of organic pollutants is capable of influencing the effects of microplastics, and the further research on the joint toxicity of microplastics with different pollutants is urgent.