ABSTRACT
While microplastics (MP) have been found in aquatic ecosystems around the world, the understanding of drivers and controls of their occurrence and distribution have yet to be determined. In particular, their fate and transport in river catchments and networks are still poorly understood. We identified MP concentrations in water and streambed sediment at fifteen locations across the Neuse River Basin in North Carolina, USA. Water samples were collected with two different mesh sizes, a trawl net (>335 µm) and a 64 µm sieve used to filter bailing water samples. MPs >335 µm were found in all the water samples with concentrations ranging from 0.02 to 221 particles per m3 (p m-3) with a median of 0.44 p m-3. The highest concentrations were observed in urban streams and there was a significant correlation between streamflow and MP concentration in the most urbanized locations. Fourier Transform Infrared (FTIR) analysis indicated that for MPs >335 µm the three most common polymer types were polyethylene, polypropylene, and polystyrene. There were substantially more MP particles observed when samples were analyzed using a smaller mesh size (>64 µm), with concentrations ranging from 20 to 130 p m-3 and the most common polymer type being polyethylene terephthalate as identified by Raman spectroscopy. The ratio of MP concentrations (64 µm to 335 µm) ranged from 35 to 375, indicating the 335 µm mesh substantially underestimates MPs relative to the 64 µm mesh. MPs were detected in 14/15 sediment samples. Sediment and water column concentrations were not correlated. We estimate MP (>64 µm) loading from the Neuse River watershed to be 230 billion particles per year. The findings of this study help to better understand how MPs are spatially distributed and transported through a river basin and how MP concentrations are impacted by land cover, hydrology, and sampling method.
ABSTRACT
Wetlands are often located in landscape positions where they receive runoff or floodwaters, which may contain toxic trace metals and other pollutants from anthropogenic sources. Over time, this can lead to the accumulation of potentially harmful levels of metals in wetlands soils. To assess the potential risk of Cu and Zn buildup in wetland soils in North Carolina, soil data from 88 wetlands were analyzed. In a subset of 16 wetlands, more intensive sampling was conducted. Samples were analyzed for Mehlich 3 Cu and Zn, and a subset of the samples was analyzed for total Cu and Zn. Overall, Mehlich 3 Cu and Zn were low, with mean values of 0.9 mg/kg for Cu and 3.2 mg/kg for Zn. Warning levels for Mehlich 3 Zn were only exceeded in three of the 88 sites; elevated Mehlich Cu was not observed. Total Cu and Zn were also low, with only a few sites having elevated levels; however, there was not a strong linear relationship between Mehlich 3 and total metals. Mean levels of Mehlich 3 Cu and Zn in wetlands were much lower than for human-impacted upland soils and background threshold concentrations that might be indicative of disturbance were much lower than warning levels for agricultural soils. The very low mobile Zn and Cu in most of these wetlands indicated that these metals do not pose a risk to the biota in most North Carolina wetlands, but wetlands with a direct and significant anthropogenic source of metal contamination could be exceptions.
