Investigation of alkyl, aryl, and chlorinated OPFRs in sediments from estuarine systems: Seasonal variation, spatial distribution and ecological risks assessment.

Estuaries in South Africa are very important for biodiversity conservation and serve as focal points for leisure and tourism activities. The organophosphate flame retardants (OPFRs) levels in these aquatic systems haven't been documented in any studies as of yet. Due to the negative effects of persistent organic pollutants in South African estuaries, we examined the occurrence of eight OPFRs in sediments of two estuaries by studying their spatiotemporal distribution, season variation, and ecological risks. The Sundays Estuary (SDE), a semi-urbanized agricultural surrounding system, recorded an ∑8OPFR concentration in sediments that ranged from 0.71 to 22.5 ng/g dw, whereas Swartkops Estuary, a largely urbanized system, recorded a concentration that ranged from 0.61 to 119 ng/g dw. Alkyl-OPFRs were the prevalent homologue in both estuaries compared to the chlorinated and aryl groups. While TBP, TCPP, and TCrP were the most abundant compounds among the homologue groups. There was no distinct seasonal trend of ∑8OPFR concentration in either estuary, with summer and autumn seasons recording the highest concentrations in SDE and SWE, respectively. Ecological risks in the majority of the study sites for the detected compounds were at low (RQ < 0.1) and medium levels (0.1 ≤ RQ < 1) for certain species of fish, Daphnia magna and algae. However, the cumulative RQs for all the compounds had ∑RQs ≥1 for most sites in both estuaries, indicating that these organisms, if present in both estuaries, may be exposed to potential ecological concerns due to accumulated OPFR chemicals. The scope of future studies should be broadened to include research areas that are not only focus on the bioaccumulation patterns of these compounds but also find sustainable ways to reduce them from these estuarine environments.

Heavy metal compartmentalisation in salt marsh and seagrass of the urbanised Swartkops estuary, South Africa.

Wetland plants are naturally exposed to high metal concentrations, and often have mechanisms to prevent metal toxicity. This study compared metal concentrations in seagrass (Zostera capensis) and salt marsh (Spartina maritima, Salicornia tegetaria) - to determine their niche as metal sinks. Samples were collected in each season over a year at five sites in the estuary and analysed using a Total X-Ray Fluorescence (TXRF) spectrometer. Spartina maritima and S. tegetaria accumulated in their roots, and displayed little translocation to leaves (BCF = 1-14; TF[leaf/root] < 1). Contrastingly, Z. capensis showed high uptake to its leaves (TF[leaf/root] = 1-8; Mn, Zn, Cr, Pb, Ni, Cu). Spartina maritima and S. tegetaria were identified as good phytostabilisers (BCF > 1, TF[leaf/root] < 1). Compartmentalization was unique to each species, and considering their ecosystem service importance, more plant species should be analysed to estimate their ecological value for management purposes.

Tissue distribution, dietary intake and human health risk assessment of organophosphate pesticides in common fish species from South African estuaries.

This study assessed the tissue distribution, dietary intake, and potential health risks of eight OPPs in Pomadasys commersonnii (Spotted grunter) and Mugil cephalus (Flathead mullet) from the Sundays and Swartkops estuaries in South Africa. The highest concentration in fish tissues was found in muscles of M. cephalus (178 ± 80.4 ng/g ww) and P. commersonnii (591 ± 280 ng/g ww) from Sundays Estuary. The ∑6OPPs concentration in muscles from both fish species was higher in muscles than in the gills with fenitrothion dominating the distribution profile. Results from the path analysis indicate that lipid, weights, and length of the fish species do not influence the concentration of OPPs in the studied fish species. The calculated hazard ratios, which represent the non-carcinogenic risks, were less than one for all OPPs, indicating that the concentration of OPPs detected in fish muscles had negligible consequences on human health.

Organophosphate pesticides in South African eutrophic estuaries: Spatial distribution, seasonal variation, and ecological risk assessment.

The seasonal variation, spatial distribution, and ecological risks of thirteen organophosphate pesticides (OPPs) were studied in the Sundays and Swartkops estuaries in South Africa. Ten pesticides were detected in surface water samples from both estuaries, while all OPPs were detected in sediments. The highest concentration of OPPs (18.8 µg pyrazophos L-1) was detected in surface water samples from Swartkops Estuary, while 48.7 µg phosalone kg-1 dw was the highest in sediments collected from Sundays Estuary. There was no clear seasonal pattern in OPPs occurrence in surface water from both systems. However, their occurrence in sediments was in the following order: winter > autumn > summer > spring, perhaps indicating major pesticide input in the winter seasons. Results from ecological risk assessment showed that pyraclofos and chlorpyrifos (CHL) in surface water from both systems are respectively likely to cause high acute and chronic toxicity to fish (risk quotient - RQ > 1). For sediments of both estuaries, the highest acute and chronic RQs for fish were calculated for isazophos and CHL respectively. The majority of the detected OPPs in sediments posed potential high risks to Daphnia magna from both systems. These results suggest that these aquatic organisms (fish, and Daphnia), if present in the studied estuaries, can develop certain forms of abnormalities due to OPP exposure. To this end, proper measures should be taken to reduce OPP input into the estuarine systems.

Organophosphate pesticides sequestered in tissues of a seagrass species - Zostera capensis from a polluted watershed.

Organophosphate pesticides (OPPs) are persistent in the environment, but little information is available on their bioaccumulation in seagrass. In this study, the seagrass - Zostera capensis was collected from Swartkops Estuary in South Africa to investigate the bioaccumulation of OPPs from contaminated sediments and the water column. This plant was chosen because it grows abundantly in the estuary's intertidal zone, making it a viable phytoremediator in the urban environment. Extraction was performed by the QuEChERS method followed by GC-MS analysis. The mean concentration of ∑OPPs ranged from 0.01 to 0.03 µg/L for surface water; 6.20-13.35 µg/kg dw for deep-rooted sediments; 18.79-37.75 µg/kg dw for leaf tissues and 12.14-39.80 µg/kg dw for root tissues of Z. capensis. The biota-sediment accumulation factors (BSAFs) were greater than one, indicating the potential for Z. capensis to bioaccumulate and intercept the targeted pesticides. A weak insignificant correlation observed between log BSAFs and log Kow indicates that the bioaccumulation of OPPs in tissues of Z. capensis were not dependent on the Kow. Eight of the selected pesticides had root-leaf translocation factors (TFr-l) greater than 1, indicating that Z. capensis can transport these chemicals from roots to leaves. The results from this study implies that this plant species can clean up OPP contamination in the environment.

A translocation analysis of organophosphate pesticides between surface water, sediments and tissues of common reed Phragmites australis.

This study investigated the ability of common reed, Phragmites australis to take up organophosphate pesticides (OPPs). The study site was the agriculturally polluted Sundays Estuary in South Africa. Surface water, leaves, roots, and deep-rooted-sediments of P. australis were collected along the length of the estuary and analysed for 13 different OPPS. The extraction of OPPs in plant tissues was performed by QuEChERS method followed by GC-MS analysis. The highest concentration of OPPs was found in leaves (16.41-31.39 µg kg-1 dw), followed by roots (13.92-30.88 µg kg-1 dw), and sediments (3.30-8.07 µg kg-1 dw). Of the 13 targeted OPPs, only one compound was not detected across the four sample matrices, thus reflecting widespread contamination in the Sundays Estuary. The biota sediment accumulation factor (BSAF) values of pyraclofos, quinalphos, fenitrothion, phosalone, EPN, diazinon, chlorpyrifos, pyrazophos, and isazophos were higher than one implying that P. australis possesses the ability to bioaccumulate these compounds. The root-leaf translocation factors (TFr-l) of these pesticides were higher than 1, suggesting that P. australis possesses the capacity to move these pesticides from roots to leaves. The insignificant correlation observed between log BSAF and log Kow and log TFr-l and log Kow implies that OPPs uptake by P. australis tissues were not dependent on log Kow. Our study demonstrates that P. australis possesses the potential to effectively remove OPPs from contaminated water and sediment.

The state of persistent organic pollutants in South African estuaries: A review of environmental exposure and sources.

The long-term health of many South African estuaries is impacted by pollutants entering these systems through industrial and agricultural runoff, sewage outfalls, contaminated storm water drainage, flows from informal settlements, and plastic materials in marine debris. Uncontrolled inputs combined with poor environmental management often result in elevated levels of persistent organic pollutants (POPs) in affected estuaries. Data on POPs research from 1960 to 2020 were analysed in terms of their sources, environmental investigations, and health implications. The outcome showed polychlorinated biphenyls (PCBs) and per- and poly-fluoroalkyl sulphonates (PFASs) to exceed the US EPA health advisory levels for drinking water. Concentration of organochlorine pesticides (OCPs) in water were below the WHO limits, while those in fish tissues from most estuaries were found to be below the US FDA limits. Although environmental compartments in some estuaries (e.g. Rooiels and uMngeni estuaries) seem to be less contaminated relative to other marine systems around the world, many others were polluted and critically modified (e.g. Durban Bay, Swartkops, Sundays, and Buffalo systems). Due to inconsistent monitoring methods coupled with limited data availability, temporal trends were unclear. Of the 290 estuaries in South Africa, 65 were prioritised and recommended for POPs evaluation based on their pollution sources, and a monitoring strategy was defined in terms of sampling. Government policies to curb marine pollution need to be enforced to prevent chronic contamination that leads to water quality deterioration and loss of ecosystem services.