title: Identification and quantification of microplastics in wastewater treatment plant effluent: Investigation of the fate and biological effects
Creators: name: Ziajahromi, Shima
Publisher: name: Griffith University
Year: 2018
Subjects: subject: Dose-related effects
subject: Environmental relevant concentration
subject: Mixture effects
subject: PE beads
subject: PET fibers
subject: Sampling device
subject: Wastewater-based microplastics
subject: Wastewater effluent
subject: Size-related effects
subject: Sorption

description: Microplastics (i.e., plastics particles &lt; 5mm) are widespread emerging contaminants that have been detected in various aquatic environments worldwide including freshwater and marine ecosystems. Contamination of the environment with microplastics has become an environmental issue due to the potential of plastics to remain for thousands of years and to accumulate in the aquatic environment. The abundance of microplastics in the aquatic environment is assumed to increase due to continuous fragmentation of macro and microplastic debris, which can lead to a decrease in the average size ranges of microplastics over time (Cole et al., 2011). Moreover, concerns have been raised regarding the potential of microplastics to physically (e.g., blockage of digestive tract) and chemically (e.g., leaching of sorbed chemicals and toxic additives) harm aquatic organisms. Microplastics can enter the aquatic environment from both aquatic-based and landbased sources. Recently, wastewater treatment plants (WWTP) have been identified as one of the important land-based sources of microplastics. While microplastics have been reported in WWTP effluent in Asia, Europe, USA and Russia, little is known about the presence of microplastics in Australian WWTP effluent. More importantly, the lack of standardized techniques to sample and characterize microplastics in environmental samples, especially in complex samples such as wastewater, has led to inaccurate estimations of microplastic concentrations. In response to the current knowledge gaps, a novel validated high-volume sampling device was developed for in situ fractionation of microplastics from wastewater effluent as part of this project. The developed method was applied to three Australian WWTPs utilizing primary, secondary and tertiary treatments to provide a snapshot of the fate and removal of microplastics during various wastewater treatment processes. To achieve an accurate estimation of microplastics, the sampling technique was combined with an efficient sample processing method. Microplastic polymer type, shape and potential origin were further determined using microscopy analysis and Fourier Transform Infrared (FTIR) spectroscopy. The efficiency of the sampling device was found to be between 92 to 99% for 500 and 25 μm mesh screens. The results showed that the concentrations of microplastics were 1.5, 0.6 and 0.2 microplastics per liter of effluent in primary, secondary and tertiary effluent, respectively. It was also found that the majority of detected microplastics in the studied WWTPs were polyethylene terephthalate (PET) fibers, which is assumed to originate from synthetic clothing. Polyethylene (PE) beads and fragments, which may be associated with cosmetic products, were the second most frequently detected type of microplastic. Despite a thorough sample processing method, FTIR spectroscopy revealed that between 22 to 90% of the suspected microplastic particles were in fact non-plastic particles. This study suggests that WWTPs can act as a significant source of microplastics to the aquatic environment given the large volume of wastewater discharged to the aquatic environment. To date, the effects of microplastics on aquatic organisms have mostly been examined using high and often unrealistic concentrations of microplastics (e.g., milligram per liter range). Moreover, while the presence of different types of microplastics together in aquatic ecosystems has been widely reported, the potential effects of microplastics when they occur as mixtures are largely unknown. To cover these knowledge gaps, the potential adverse effects of wastewater-based microplastics (such as fibers and beads) at lower concentrations on the freshwater organism Ceriodaphnia dubia were evaluated. The acute (48 h) and chronic (192 h) effects of PET fibers and PE bead microplastics on C. dubia were assessed alone and as a binary mixture. The results showed a dose-dependent trend on survival, with C. dubia more sensitive to PET fibers than PE microplastics. The 48 h EC50 value of fibers was 1.5 mg/L compared to 2.2 mg/L for PE beads. The binary mixture of microplastic beads and fibers demonstrated less than additive effects. EC50 values for the chronic bioassay were 429 μg/L for fibers and 958 μg/L for PE microplastics. A positive trend of decreasing growth (body size of adults) and reproduction rate (number of neonates) with increasing microplastic concentration was observed for both PE and fiber microplastics during the chronic bioassays. Using scanning electron microscopy (SEM) we observed deformities, such as carapace and antenna deformation, in C. dubia exposed to fibers at a high concentration, but not at the lower (environmentally relevant) concentrations. Given the likelihood that microplastics will eventually sink to the bottom sediment in the aquatic ecosystem the effects of microplastics were investigated on a freshwater sediment-dwelling organism (Chironomus tepperi) at environmentally relevant concentrations of PE microplastics (500 particles/kgsediment). Possible size-dependent effects of microplastics were also examined using four different size ranges of PE beads including 1-4, 10-27, 43-54 and 100-126 μm. The results revealed that exposure to an environmentally relevant concentration of microplastics had a detrimental impact on the survival, growth (i.e., body length and head capsule) and emergence of C. tepperi. The observed effects were strongly dependent on microplastic size with C. tepperi more sensitive to microplastics in the size range of 10-27 μm. No negative effects were observed on growth and survival of C. tepperi exposed to the larger microplastics (100-126 μm), though a significant decrease in the number of emerging adults was observed in the organisms exposed to the same size range of microplastics. Further, SEM showed a significant reduction in the size of the head capsule and antenna in C. tepperi exposed to microplastics in the size range of 10-27 μm. These results showed that environmentally relevant concentrations of microplastics in sediment can result in adverse effects on the development and emergence of C. tepperi, with effects strongly dependent on particle size. Finally, we evaluated the effects of PE microplastics on the acute toxicity of a pyrethroid insecticide (bifenthrin) to midge larvae (C. tepperi) in water. To test the single and combined effects of bifenthrin and PE microplastics, C. tepperi larvae were exposed to six concentrations of bifenthrin ranging from 0.1 to 3.2 μg/L in the presence and absence of microplastics. To examine the possible effects of bifenthrin and microplastics in synthetic and real water, the bioassays were performed in both moderately hard water (MHW) and river water. We performed an uptake study using three different size ranges of microplastics (10-27, 43-54, 100-126 μm) during 8-day microplastics-spiked water exposure. The results showed that microplastics in the size range of 10-27 μm were mostly ingested by C. tepperi larvae. Using this finding, 10-27 μm microplastics were selected for the bioassays. The results of the bioassays using MHW demonstrated a significant decrease in the toxicity of bifenthrin in the presence of microplastics. This is likely attributable to the tendency of bifenthrin to bind to the microplastics, which reduces the bioavailability of bifenthrin to midge larvae. However, in the bioassays conducted in river water with a total organic carbon (TOC) concentration of 9.6 mg/L, no significant difference was observed between the toxicity of bifenthrin to C. tepperi in the presence and absence of microplastics. This is likely due to the interaction between organic carbon and bifenthrin, which reduces the bioavailability of bifenthrin to C. tepperi larvae. This thesis highlights that microplastic fibers and beads are released to the aquatic environment from WWTPs, and that this can negatively affect survival, reproduction and the life cycle of aquatic organisms (both pelagic and benthic) through entanglement (fibers) and ingestion (beads). The effect of microplastics on chemical contaminants is complex, and microplastics may act both as carriers but also as “chelators” of chemicals in the water, thereby reducing their bioavailability.