May a Former Municipal Landfill Contaminate Groundwater in Microplastics? First Investigations from the “Prairie de Mauves Site” (Nantes, France)

Abstract

Municipal landfills receive a high amount of plastic waste and due to the occurring physical and biochemical degradation processes, could be significant sources of microplastics (MP). Evaluating the threat to groundwater through the transfer of MP via landfill leachates require more research. The former “Prairie de Mauves” landfill, operated from 1963 to 1987 by the municipality of Nantes (France), and located above the alluvial groundwater of the Loire River, represents a good candidate for such investigations. Leachates and groundwater were sampled along a transect line from upstream to downstream of the landfill, in March and June 2022. MP (>25 µm) were quantified and characterized using µFTIR imaging in transmission mode. MP were observed in every sample with concentrations ranging from 0.71 to 106.7 MP/L. Concentrations in the leachates and the alluvial groundwater illustrate a migration of MP. Twelve polymers were identified and polyethylene (PE) and polypropylene (PP) were predominant. After a conventional rainfall event (14.3 mm), higher concentrations, diversity, and size ranges of MP were observed. Water infiltration through the heterogeneous geological substratum therefore enhanced the migration of larger MP towards the alluvial groundwater of the Loire River.

Microplastics in Groundwater: Pathways, Occurrence, and Monitoring Challenges

“…There appears to be a lack of specific guidelines in the literature for determining the optimal depth for sampling in a well or below the GW table. In some articles, the depth at which sampling was performed is not mentioned [109,110,113]. Selvam et al [2] state that sampling was carried out at a depth of 2-5 m. Samandra et al [108] report that sampling was performed at the mid-point of the screened interval of the boreholes.…”

“…Recent studies have identified various MP contamination sources in GW, including septic tanks, landfills, sewage treatment plants, and agricultural areas [109,[113][114][115]. A significant correlation has been found between MP abundance in GW and the total concentration of antibiotics, proving that sewage treatment plants are a source of contamination [109].…”

“…Informal landfills, which are built without proper construction and operated with a lack of environmental protection measures, are a cause for concern due to their insufficient protection and poor management [115]. Wan et al [115] found a concentration of 11 to 17 MP/L of MPs in GW around an informal landfill, while Leideu et al [113] investigated the presence of MPs in GW around a former municipal landfill located in an alluvial aquifer and found even wider concentration range of 0.71 to 106 MP/L. In addition, a study from Chennai, South India, reported higher levels of MPs in GW samples in the vicinity of municipal solid waste landfills, ranging from 2 to 80 MP/L [114].…”

“…Sample volume in the studies included in this review [2,25,[108][109][110][113][114][115] ranged from one to twenty litres. When measuring MPs, a small sample volume can lead to an overestimation [118].…”

“…Typically, the pumping systems also contain plastic parts that can potentially contaminate the sample. Of the articles analysed, only one indicates the use of Teflon-made pumps [2], while some [112,113,121] mention the type of pump used without specifying its material composition. All components of the pumping system need to be specified with regard to their material structure using FTIR analysis.…”