Fate of nanoplastics and their effects on ecosystem functions in constructed wetlands

Abstract

The production of plastics has seen incredible growth in recent years. Accordingly, the release of plastic particles (micro and nano) into the environment is also increasing. Information on environmental, biological concentrations, and the fate of nanoplastic (NP) in aquatic environments are scarce. Most in vitro studies have been investigating the effects of NPs at higher exposure concentrations and have not considered the community level response under natural conditions. This study focused on investigating the effects of polystyrene (PS) NPs on ecosystem functions and the distribution of NPs in wetland ecosystems. The study was performed in a replicated semi-natural wetland ecosystem with a mesocosm approach during 10 weeks of exposure to engineered NP particles (87 ± 10 nm) with a gold (Au) core to enable detection using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). The study showed no effect of PS NPs exposure (243 µg/L) on primary production or decomposition by microorganisms whereas respiration was increased significantly. Extrapolated PS NPs concentrations were shown to have an accumulation in both biota and sediment. PS NPs were taken up by the macroinvertebrate Asellus aquaticus but did not affect to their population nor the decomposition driven by them. Accumulation of PS NPs was observed in both macrophytes, Carex sp. and Juncus sp., while roots showed higher accumulation than above ground vegetation. Considering species, Juncus sp. was shown to have higher uptake of PS NPs. Significantly higher accumulation was observed in lake sediment while discharge from wetland showed a lower PS NPs concentration. This study with the quantitative assessing method of NPs aid in forecasting where they could end up in a natural wetland ecosystem.

Popular Abstract

Fate of nanoplastics and their effects on ecosystem functions in constructed wetlands

Since the invention of plastic, the production and use of plastics are continuously growing. A considerable amount of produced plastics is ending up in the environment as waste. When these plastics are in the environment they are broken down into smaller particles, interestingly into nanometer scale. Those tiny plastics are known as nanoplastics and the said pathway to form nanoplastic is called the secondary source. The plastics that are manufactured already in the nanoscale are considered the primary source of nanoplastics. However, nanoplastics have gained traction during the last decades due to their higher surface-to-volume ratio, various sizes, and shapes. They have been found to make toxic effects on organisms and they are passed through the food chains. Ecosystem functions like photosynthesis and decomposition driven by microorganisms are also found to be affected by nanoplastics in laboratory conditions but mostly not focused on the community responses. It is hard to find information on how nanoplastics behave in natural water bodies like lakes, and wetlands, how much nanoplastics are available in different environments and organisms in food chains. The reason behind this is, there is no standard method to differentiate nanoplastic particles from the natural environment because they are too small and no standard method to quantify them.

One possible way to overcome this, until finding the standard methods to separate and measure nanoplastics, is to use metal inside of nanoplastic particles and observe their behavior under more natural conditions. Since standard analytical methods have already been developed to quantify metal, it could trace the amount of plastics based on the quantity of metal. That will provide a base to predict the possible behavior and accumulations of nanoplastics in a natural environment. In this study, gold metal was used as the core of polystyrene nanoplastic particle and twelve aquaria were built providing all the natural conditions as in an actual wetland. Nanoplastics were added to six aquaria once a week for ten weeks of the study period. The effects of nanoplastics exposure on photosynthesis, respiration and decomposition were observed. Photosynthesis and decomposition of the microorganism community were not affected by the nanoplastics exposure, but respiration was increased. The gold content was determined in the analytical equipment called Inductively Coupled Plasma Mass Spectroscopy. So that, the study found where the nanoplastics were ended up in the wetland and nanoplastics accumulation in organisms living in the lake bottom, like Asellus aquaticus and in wetland plants i.e., Carex sp and Juncus sp. Plastics have seemed to more accumulated in the lake bottom than in other areas of the wetland sediment. Both plants and A. aquaticus were shown the uptake of nanoplastics. But the nanoplastics exposure has not had an impact on the population of A. aquaticus and the decomposition driven by them. The roots of both plants were shown higher nanoplastic accumulation than their above ground materials. Juncus sp. was seemed to have higher uptake than Carex sp. Further, discharge from wetland had a lower nanoplastics content saying most of the added nanoplatics were retained in the wetland.

In this study, the water in the lake was subjected to continuous input and output flow, the toxicity coming from the polluted water in the study may be diminished as the exposure concentration is varied. Also, higher accumulation in the lake sediment provided a lower amount of nanoplastics in the water column of the lake. Further, community response to nanoplastic exposure in the simulated wetland environments may come as a cumulative response of both species-specific sensitivity and competition between species. Nanoplastic’ behavior and its effects differ with the properties of the particles and the aqueous media. Therefore, further studies are encouraged and required in an environmentally realistic way to conclude nanoplastics’ behavior and effects on ecosystems. However, current results with the quantitative assessing method of nanoplastics are a step forward to measure environmental and biological concentrations and the possible effects on aquatic environments by simulating the actual environment.

Master’s Degree Project in Biology/Biology/Aquatic Ecology 30 credits 2021
Department of Biology, Lund University

Advisor: Mikael Ekvall Co-Advisor: Franca Stábile
Advisors Unit/Department: Aquatic Ecology Division

• author: Soorasena, Chalani
• supervisor: Mikael Ekvall; Franca Stábile
• organization: Degree Projects in Biology
• course: BIOM02 20211
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 9075477
• date added to LUP: 2022-02-16 17:04:25
• date last changed: 2022-02-16 17:04:25