No abstract

Microplastic pollution is concerning because it is widespread in aquatic environments and there is growing evidence of negative biological effects. Here, we present one of the first studies to examine microplastic pollution (plastic particles <1 mm) in urban wetlands and investigate relationships between contamination and urban land use. Sediment samples were collected from twenty independent urban wetlands, each with different types of urban land use within their catchments. Microplastics were observed at all wetlands, with an average abundance of around 46 items/kg of dry sediment. Plastic fragments were the most common type of microplastic, accounting for 68.5% of all microplastics found. Consistent with other studies, microplastic abundance was positively correlated with increased catchment urbanisation. On closer examination, plastic fragments and beads correlated with catchment urbanisation. Fragment abundance also increased in wetlands with catchments that had a higher proportion of industrial land use and decreased in catchments with higher residential densities. This study demonstrates the susceptibility of urban wetlands to microplastic pollution, further highlighting the ubiquitous nature of microplastic pollution. The prevalence of microplastic fragments indicates that plastic litter degradation is a significant source of microplastics in urban environments, especially in industrial areas.

Aquatic sediments act as a sink for pollutants that potentially impact on aquatic communities. However, spatial correlations between pollution, hydrology, catchment disturbance and other factors make it difficult to determine the impact of sediment pollution. Field-based microcosm experiments utilising aquatic macroinvertebrates are one approach to isolating the biological effects of sediment pollution on aquatic biota. A field-based microcosm experiment was used to assess the effects of sediment from 14 sites along the River Murray system, Australia. Aquatic ecosystem declines have been observed in this river, but few studies have investigated the quality of its sediments or their biological impact. Chironomidae (midge larvae) dominated the microcosm experiment and were useful as bioindicators of sediment quality. Community composition, high incidences of larval mouthpart deformities in Procladius paludicola and skewed sex ratios in Tanytarsus fuscithorax indicated sediments from irrigation districts were having a toxic effect, but only nutrients were detected at biologically relevant concentrations and these did not correlate with species responses. The present study showed that the biological endpoints used in the microcosm approach can elucidate sediment toxicity even in the absence of supporting sediment chemistry and could successfully be applied to examine changes in sediment quality along a river system.

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Metabolomic techniques are powerful tools for investigating organism-environment interactions. Metabolite profiles have the potential to identify exposure or toxicity before populations are disrupted and can provide useful information for environmental assessment. However, under complex environmental scenarios, metabolomic responses to exposure can be distorted by background and/or organismal variation. In the current study, we use LC-MS (liquid chromatography-mass spectrometry) and GC-MS (gas chromatography-mass spectrometry) to measure metabolites of the midge Procladius villosimanus inhabiting 21 urban wetlands. These metabolites were tested against common sediment contaminants using random forest models and metabolite enrichment analysis. Sediment contaminant concentrations in the field correlated with several P. villosimanus metabolites despite natural environmental and organismal variation. Furthermore, enrichment analysis indicated that metabolite sets implicated in stress responses were enriched, pointing to specific cellular functions affected by exposure. Methionine metabolism, sugar metabolism and glycerolipid metabolism associated with total petroleum hydrocarbon and metal concentrations, while mitochondrial electron transport and urea cycle sets associated only with bifenthrin. These results demonstrate the potential for metabolomics approaches to provide useful information in field-based environmental assessments.