An understanding of the relationships between plastics and plasticizers is vital in order to assess their environmental risk. We investigated spatial trends and relationships between microplastics and plasticizers in sediments of an urbanized estuary subject to contemporary and historic sources of contamination (Forth estuary, Scotland, UK). As such, this study represents one of the first to investigate the co-occurrence of emerging plasticizers, phthalates, and microplastics in an estuary system. We determined the concentration of 7 legacy (phthalate) and 3 emerging (adipate, terephthalate, trimellitate) plasticizers and 21 microplastic polymer types. The most abundant microplastics were polyethylene (PE), polypropylene (PP), polyurethane (PU), and poly(vinyl chloride) (PVC). Plasticizers were dominated by diethylhexyl phthalate (DEHP), although emerging plasticizers (e.g., diethylhexyl terephthalate, DEHTP) were frequently detected at low concentrations (mean 7.3 ng g-1 ww). There was strong evidence that concentrations of microplastics and plasticizers were significantly lower in the outer estuary. However, we found no evidence for a spatial relationship between the concentration of microplastics and plasticizers at individual site level. Our results indicate that microplastics in the size range analyzed (∼25-1000 μm) may not be a good predictor of the spatial distribution of plasticizers in estuaries. This could result from release of plasticizers prior to plastic fragmentation and deposition and differences in transport and fate.
Billings et al. (2025) studied this question.