Comparative Assessment of Microplastics in Surface Waters and Sediments of the Vaal River, South Africa: Abundance, Composition, and Sources

Abstract

We extracted microplastics from surface water and sediment samples from the Vaal River in Johannesburg, South Africa. Average abundances of 0.61 ± 0.57 particles/m 3 and 4.6 × 10 2 ± 2.8 × 10 2 particles/kg dry weight were recorded for water and sediment samples, respectively. In both sediment and water samples, more than 80% of microplastics were fragments and fibers of smaller than 2 mm. High-density polyethylene, low-density polyethylene, and polypropylene were the dominant polymers identified in both sample types. In addition, polyethylene co-vinyl acetate, polyester, polyurethane, and polyethylene/ hexene-1-copolymer were also detected in sediment samples. Colored microplastics were the most commonly observed in both sample types; pigment yellow 83 was detected in surface water, and carbon black was detected in both sediment and water samples during Raman analysis. Taking into consideration the physical and chemical characteristics of the detected microplastics, their potential sources include inflow from tributaries, surface run-off from urban city centers, recreational activities, and wastewater effluent from industries and households.

Microplastic pollution in Africa: an overview of abundance in aquatic organisms, freshwater and marine water environments and analytical methods for reporting

“…They found MPs types as PE (both high and low density), PP, and polyethylene co-vinyl acetate (PEVA), polyester (PES), polyurethane foam (PU), and polyethylene/hexene-1-copolymer (PEH). A similar study conducted by Ramaremisa et al. (2022) in the Vaal River found MPs abundance of 0.61 ± 0.57 particles/m 3 in surface water and 4.6 × 10 2 ± 2.8 × 10 2 particles/kg dry weight in sediment samples.…”

Microplastic Abundance and Sources in Surface Water Samples of the Vaal River, South Africa

“…Twenty surface water samples were collected, and the sampled material was concentrated inside a removable net bucket with a sieve gauze-covered side window and stop-cock, through which it was transferred into glass jars. GPS and flowmeter readings at the beginning and the end of each tow were recorded and the volume filtered through the net was calculated using a flowmeter (General Oceanics model 2030R) attached to the net (Ramaremisa et al 2022 ). Samples were stored in glass jars, transferred to the laboratory, and preserved at 4 °C.…”

“…The samples were subsequently swirled to allow the solution to soak into the sample. Samples were left for 24–48 h at room temperature to achieve complete digestion before separation (Ramaremisa et al 2022 ).…”

“…Upon digestion, MPs were separated based on their density using both NaCl and NaI, in a two-step density separation protocol (Ramaremisa et al 2022 ). Firstly, 45 mL of saturated NaCl (1.2 g/mL) was mixed with each sample, left for 24 h, and filtered.…”

Methods for controlled preparation and dosing of microplastic fragments in bioassays

“…The persistence of microfragments is not just limited to coastal marine environments. Microfragments were also among the most common microplastic shapes sampled in lakes 26,27 , rivers [28][29][30] , and terrestrial sediments 31 throughout the world. Furthermore, microplastic fragments have been found inside seabirds 32,33 , fish 34,35 , mussels 36,37 , and crustaceans 38,39 , illustrating their bioavailability once they enter the environment.…”