Seasonal variations of microplastic in sediment, Chironomus sp. larvae, and chironomid tubes in two wastewater sites in Sohag Governorate, Egypt

Abstract

Microplastic (MP) contamination is an acknowledged global problem that poses a severe risk to aquatic ecosystem biota. Nevertheless, little is known about their prevalence in animal construction. The main objective of our study was to reduce the gap information of seasonal abundance, distribution, composition, and risk assessment of MP contamination. The concentrations of MPs in sediment, Chironomus sp. larvae, and their tubes were found to be higher in site 2 (S2) than in site 1 (S1) during the four seasons of the year. However, MP concentrations ranged from 312 ± 64.7 to 470 ± 70 items/kg dry weight, 0.79 ± 0.16 to 1.1 ± 0.3 particles/individual, and 0.5 ± 0.04 to 0.9 ± 0.04 particles/tube in sediment, Chironomus, and chironomid tubes, respectively. Blue and red polyester fibers are the most dominant MPs which are distributed in sediment, Chironomus, and chironomid tubes. The length of the dominant fiber accumulates in Chironomus, and their tubes are highly varied compared to that of the substrate. Additionally, we found that the mean number of MPs/individual larvae in the fourth instar was significantly higher than that in the second instar. Risk indicators for the environment, polymer risk assessment, and pollution load were estimated, where they were higher in S2 than in S1 correlated to MPs abundance and polymer type. The seasonal fluctuation in MP concentration, characterization, and risk in the two sites could depend on the amount of sewage effluent discharged into the wastewater treatment plants (WWTPs), which was reflected by Chironomus sp. larvae. Therefore, further research should be done to adopt the applicability of Chironomus as MP bioindicators in various freshwater environments throughout the world.

Keywords: Chironomid tube; Chironomus sp.; Microplastic; Sediment; Wastewater.

Fig. 1

Egypt map showing Sohag Governorate (A). Google Earth photo showing the collecting sites (B)

Fig. 2

Mean seasonal abundance of MPs in the sediment of the two sites of wastewater

Fig. 3

Photographs showing different shapes of microplastics obtained from sediment (A and B), Chironomus sp. (C), and chironomid tubes (D). (A) fragments and (B–D) fibers. The scale bar = 250 µm

Fig. 4

The percentage of the different microplastic shapes (A), lengths (B) with µm, colors(C), and chemical composition (D) collected from the sediment of the two wastewater sites

Fig. 5

Micro-FTIR spectra of representative microplastic polymers extracted from sediment, Chironomus sp. larvae, and their tubes (PES, polyester; PE, polyethylene; and PP, polypropylene)

Fig. 6

Mean seasonal abundance of MPs per individual of Chironomus sp. (A) and per chironomid tube (B) collected from the two sites of wastewater

Fig. 7

Relationship between the mean number of MPs per kg in sediment and per individual of Chironomus sp. larvae of the two wastewater sites

Fig. 8

The percentage of the different microplastic shapes (A), lengths (B) with µm, colors(C), and chemical composition (D) collected from Chironomus sp. larvae and their tubes (chironomid tube) of the two wastewater sites

Fig. 9

The relative abundance of MP size distribution across Chironomus sp. collected from the two wastewater sites

Fig. 10

Whole body shape (A, B), head capsule (C, D), and mentum (E, F) of second (L2) and fourth (L4) instar larva of Chironomus sp., respectively