Bioindicator-based multi-decadal study (1980–2021) of microplastic pollution in an estuarine system of the Bay of Biscay using Hediste diversicolor (O.F. Müller, 1776)

Plastic production has increased exponentially since the 1950s, leading to widespread contamination of marine environments. Microplastics (MPs), originating from both manufactured products and the fragmentation of larger plastics, pose particular risks to benthic organisms. In this study, we conducted a trend analysis of the evolution of the presence, quantity, typology, and distribution of ingested MPs of Hediste diversicolor (a key estuarine polychaete) from 1980 to 2021 in the Partial Nature Reserve of the Villaviciosa estuary (Bay of Biscay). Hediste diversicolor specimens were identified based on combined morphological and molecular analyses of the COI gene. Results show a consistent concentration of MPs over the last five decades. However, smaller individuals contained significantly higher MP concentrations per unit mass. The estimated sources of these MPs were 68.58% from the textile industry, 2.32% from the marine industry, 16.26% from other industries and 12.79% from the food and packaging sector. This indicates early contamination by microplastics in the environment and reflects the problem of the textile industry. These findings suggest that local human activities and species-specific traits exert greater influence on MP accumulation than global production trends.