Decadal Assessment of Microplastics, Pharmaceuticals, and Pesticides as Contaminants of Emerging Concern in Kenya's Surface Waters: A Review

Studies investigating microplastics, pharmaceuticals, and pesticides as contaminants of emerging concern (CECs) in surface water sources in Kenya are reviewed. Contaminants of emerging concern are chemicals that have recently been discovered that may pose a threat to the environment, aquatic life, and human life. Microplastics in surface waters range from 1.56 to as high as 4520 particles/m3 , with high concentrations recorded in coastal waters. The dominant microplastics are fibers, fragments, and films, with foams, granules, and pellets making up only a small percentage. The main source of pharmaceuticals in water sources is not wastewater-treatment plants but rather raw untreated sewage because high concentrations are found near informal settlements with poor sewage connectivity. Antibiotics are detected in the range of the limit of quantification to 320 μg/L, with sulfamethoxazole, trimethoprim, and ciprofloxacin being the most abundant antibiotics. The high frequency of detection is attributed to the general misuse of antibiotics in the country. A health risk assessment indicated that only ciprofloxacin and acetaminophen posed noncarcinogenic health risks in the Ndarugo River and Mombasa periurban creeks, respectively. Similarly, the detection of antiretroviral drugs, mainly lamivudine, nevirapine, and zidovudine, is associated with human immunodeficiency virus prevalence in Kenya. In the Lake Naivasha, Nairobi River, and Lake Victoria basins, frequently detected organochloride pesticides (OCPs) are methoxychlor, alachlor, endrin, dieldrin, endosulfan, endosulfan sulfate, α-hexachlorocyclohexane (α-HCH), γ-HCH, and dichlorodiphenyltrichloroethane (DDT), some of which occur above permissible concentrations. The presence of DDT in some sites translates to illegal use or historical application. The majority of individual OCPs posed no noncarcinogenic health risk, except dieldrin and aldrin which had a hazard quotient >1 in two sites. Therefore, more surveying and regular monitoring in different regions in Kenya concerning CECs is essential to determine the spatial variability and effective measures to be taken to reduce pollution. Environ Toxicol Chem 2023;42:2105-2118. © 2023 SETAC.

Tracking pollutants in a municipal sewage network impairing the operation of a wastewater treatment plant

This work provides a screening of organic contaminants and characterization of the dissolved organic matter in the sewer network until the municipal wastewater treatment plant (WWTP), identifying the network areas with a higher degree of contamination and their impact on the WWTP performance, particularly in the activated sludge reactor. Three monitoring campaigns were carried out at six selected locations of the sewage system (PVZ-1, PVZ-2, PS-F, PS-VC, CP-VC, and PS-T), influent (WWTP_INF) and effluent (WWTP_EFF) of the WWTP. Advanced analytical techniques were employed, namely excitation/emission matrix fluorescence-parallel factor analysis (EEM-PARAFAC), size exclusion chromatography with organic carbon detector (SEC-OCD), and liquid chromatography with high-resolution-mass spectrometric detection (LC-HRMS). EEM-PARAFAC showed higher fluorescence intensity for the protein-like component (C2), particularly at CP-VC (near seafood industries) associated with the presence of surfactants (~50 mg/L). SEC-OCD highlighted the WWTP efficiency in removing low molecular weight acids and neutrals. LC-HRMS tentatively identified 108 compounds of emerging concern (CEC) and similar detection patterns were obtained for all wastewater samples, except for PVZ-2 (lower detection), many of which occurred in the effluent. Eight CECs included on relevant Watch-Lists were detected in all WWTP_EFF samples. Furthermore, 111 surfactants were detected, the classes more frequently found being alcohol ethoxylates (AEOs), nonylphenol polyethoxylates (NPEOs) and linear alkylbenzene sulphonates (LAS). The continuous presence of LAS and NPEOs allied to surfactants concentrations in the WWTP_INF of 15-20 mg/L, with CP-VC location (linked with food industries) as an important contributor, explain the morphological changes in the activated sludge and high LAS content in the dewatered sludge, which may have impacted WWTP performance.

Microwave regeneration of granular activated carbon saturated with PFAS

This study investigated the regeneration of PFAS-saturated granular activated carbons (GACs) by microwave (MW) irradiation. Two commercially available GACs (bituminous coal based GAC [BCGAC] and lignite coal based GAC [LCGAC]) were saturated with perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) and then irradiated at different MW conditions (applied power = 125 - 500 W, irradiation time = 3 - 12 min). The performance of MW regeneration for PFOS- or PFOA-saturated GACs was assessed by evaluating the variation of GAC adsorption capacity (regeneration efficiency, RE) and weight loss percentage (WL). Moreover, the effect of MW irradiation on GAC textural properties (e.g., surface area and pore volume) was examined through N₂ adsorption isotherms. Additionally, five successive adsorption/regeneration cycles were carried out at the MW operational condition that allowed to reach the target temperature (T>600°C) while minimizing the WL. Both GACs exhibited a strong ability to convert MW irradiation into a rapid temperature increase (~150°C min^-1 at 500 W). The highest values of RE (>90%) for both PFOA- and PFOS-saturated GACs were obtained at MW irradiation conditions that employed short regeneration time (3 min) and optimal temperature. Indeed, the highest RE did not occur at the highest temperatures (>750°C) due to the damage of GAC porous structure, particularly for LCGAC. After five cycles, the observed values of RE (~65%) and a moderate weight loss (<7%) demonstrated the good performance of MW irradiation for regenerating PFOA- and PFOS-saturated BCGAC. The obtained findings pointed out that MW irradiation is a promising alternative regeneration technique for PFAS-saturated GAC.

Comparison of the new Cl2/O3/UV process with different ozone- and UV-based AOPs for wastewater treatment at pilot scale: Removal of pharmaceuticals and changes in fluorescing organic matter

This work critically compared the removal of fluorescing PARAFAC components and selected pharmaceuticals (carbamazepine, fluoxetine, gemfibrozil, primidone, sulfamethoxazole, trimethoprim) from a tertiary wastewater effluent by different UV- and ozone-based advanced oxidation processes (AOPs) operated at pilot-scale. Investigated AOPs included UV/H₂O₂, UV/Cl₂, O₃, O₃/UV, H₂O₂/O₃/UV, and the new Cl₂/O₃/UV. AOPs comparison was accomplished using various ozone doses (0-9 mg/L), UV fluences (191-981 mJ/cm²) and radical promoter concentrations of Cl₂ = 0.04 mM and H₂O₂ = 0.29 mM. Chlorine-based AOPs produced radical species that reacted more selectively with pharmaceuticals than radical species and oxidants generated by other AOPs. Tryptophan-like substances and humic-like fluorescing compounds were the most degraded components by all AOPs, which were better removed than microbial products and fulvic-like fluorescing substances. Removal of UV absorbance at 254 (UV₂₅₄) nm was always low. Overall, chlorine-based AOPs were more effective to reduce fluorescence intensities than similar H₂O₂-based AOPs. The Cl₂/O₃/UV process was the most effective AOP to degrade all target micro-pollutants except primidone. On the other hand, the oxidation performance of pharmaceuticals by other ozone-based AOPs followed the order H₂O₂/O₃/UV > O₃/UV > O₃. UV/Cl₂ process outcompeted UV/H₂O₂ only for the removal of trimethoprim and sulfamethoxazole. Correlations between the removal of pharmaceuticals and spectroscopic indexes (PARAFAC components and UV₂₅₄) had unique regression parameters for each compound, surrogate parameter and oxidation process. Particularly, a diverse PARAFAC component for each investigated AOP resulted to be the most sensitive surrogate parameter able to monitor small changes of pharmaceuticals removal.

Ozonation effects on emerging micropollutants and effluent organic matter in wastewater: characterization using changes of three-dimensional HP-SEC and EEM fluorescence data

The degradation of effluent organic matter (EfOM) in a municipal wastewater treated by ozonation was characterized using the methods of high-performance size-exclusion chromatography (HP-SEC) and excitation/emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC). The removal of 40 diverse trace-level contaminants of emerging concern (CEC) present in the wastewater was determined as well. Ozonation caused a rapid decrease of the absorbance and fluorescence of the wastewater, which was associated primarily with the oxidation of high and low apparent molecular weight (AMW) EfOM fractions. PARAFAC analysis also showed that components C1 and C2 decreased prominently in these conditions. The EfOM fraction of intermediate molecular weight ascribable to a terrestrial humic-like component (C3) tended to be less reactive toward ozone. Relative changes of EEM fluorescence were quantified using F _max values of PARAFAC-identified components (∆F/F ⁰_max). Unambiguous relationships between ∆F/F ⁰_max values and the extent of the degradation of the examined CECs (∆C/C₀) were established. This allowed correlating main parameters of the ∆C/C₀ vs. ∆F/F ⁰_max relationships with the rates of oxidation of these CECs. The results demonstrate the potential of online measurements of EEM fluorescence for quantitating effects of ozonation on EfOM and micropollutants in wastewater effluents.