Release of high-molecular-weight plasticizers from PVC: mesocosm experiments under near-natural conditions

Background

In recent years, rapidly increasing environmental concentrations have been observed for certain high-molecular-weight (HMW) plasticizers, that are mainly used in PVC outdoor products. However, in light of their low solubility, these findings cannot be adequately explained by leaching alone. The study aimed to describe the extent of leaching and fragmentation of standardized PVC objects containing plasticizers influenced by weathering, including mechanical stress through wave action. We investigated the release behavior of the two potentially hazardous plasticizers di(2-propylheptyl) phthalate (DPHP) and tris(2-ethylhexyl) trimellitate (TOTM) from PVC in an artificial wave and pond mesocosm system under outdoor conditions over 181 days.

Results

A rapid release of DPHP and TOTM into the surrounding water was observed in the wave mesocosms (DPHP, 12.3 µg/L; TOTM, 19.8 µg/L after 24 h) with highly fluctuating concentration trends. Maximum sediment levels (DPHP, 4.12 µg/kg dry weight; TOTM, 5.43 µg/kg dry weight) were reached after 56 days. For both, water and sediment, the concentrations dropped from the shore area to the deeper water segments by > 80%. The DPHP test objects also contained a small amount of TOTM, and we observed concentration ratios of DPHP and TOTM in water and sediment samples that were highly similar to their content ratio in the test objects. In contrast, under leaching and weathering conditions in a stagnant pond and a dry gravel bed system, low levels of DPHP and TOTM were revealed in water (< 0.20 µg/L) and sediment (< 0.10 µg/kg dry weight).

Conclusions

Our data indicate, that under mechanical stress exerted through waves, the fast generation of small particles mainly influence plasticizer release, leading to an immediate occurrence of HMW plasticizers in the aqueous environment. Considering the ecological risk, particularly for coastal regions, the study documents the urgent need to sufficiently restrict their use. Furthermore, our results show that mesocosm experiments can be an integral part of research on plasticizer transfer in the environment.