Insects to the rescue? Insights into applications, mechanisms, and prospects of insect-driven remediation of organic contaminants

Traditional and emerging contaminants pose significant human and environmental health risks. Conventional physical, chemical, and bioremediation techniques have been extensively studied for contaminant remediation. However, entomo- or insect-driven remediation has received limited research and public attention. Entomo-remediation refers to the use of insects, their associated gut microbiota, and enzymes to remove or mitigate organic contaminants. This novel approach shows potential as an eco-friendly method for mitigating contaminated media. However, a comprehensive review of the status, applications, and challenges of entomo-remediation is lacking. This paper addresses this research gap by examining and discussing the evidence on entomo-remediation of various legacy and emerging organic contaminants. The results demonstrate the successful application of entomo-remediation to remove legacy organic contaminants such as persistent organic pollutants. Moreover, entomo-remediation shows promise in removing various groups of emerging contaminants, including microplastics, persistent and emerging organic micropollutants (e.g., antibiotics, pesticides), and nanomaterials. Entomo-remediation involves several insect-mediated processes, including bio-uptake, biotransfer, bioaccumulation, and biotransformation of contaminants. The mechanisms underlying the biotransformation of contaminants are complex and rely on the insect gut microbiota and associated enzymes. Notably, while insects facilitate the remediation of contaminants, they may also be exposed to the ecotoxicological effects of these substances, which is often overlooked in research. As an emerging field of research, entomo-remediation has several knowledge gaps. Therefore, this review proposes ten key research questions to guide future perspectives and advance the field. These questions address areas such as process optimization, assessment of ecotoxicological effects on insects, and evaluation of potential human exposure and health risks.

Are phenolic compounds produced during the enzymatic production of prebiotic xylooligosaccharides (XOS) beneficial: a review

Phenolics produced during xylooligosaccharide production might inhibit xylanases and enhance the antioxidant and antimicrobial activities of XOS. The effects of phenolic compounds on xylanases may depend on the type and concentration of the compound, the plant biomass used, and the enzyme used. Understanding the effects of phenolic compounds on xylanases and their impact on XOS is critical for developing viable bioconversion of lignocellulosic biomass to XOS. Understanding the complex relationship between phenolic compounds and xylanases can lead to the development of strategies that improve the efficiency and cost-effectiveness of XOS manufacturing processes and optimise enzyme performance.

Emerging organic contaminants in drinking water systems: Human intake, emerging health risks, and future research directions

Few earlier reviews on emerging organic contaminants (EOCs) in drinking water systems (DWS) focused on their detection, behaviour, removal and fate. Reviews on multiple exposure pathways, human intake estimates, and health risks including toxicokinetics, and toxicodynamics of EOCs in DWS are scarce. This review presents recent advances in human intake and health risks of EOCs in DWS. First, an overview of the evidence showing that DWS harbours a wide range of EOCs is presented. Multiple human exposure to EOCs occurs via ingestion of drinking water and beverages, inhalation and dermal pathways are discussed. A potential novel exposure may occur via the intravenous route in dialysis fluids. Analysis of global data on pharmaceutical pollution in rivers showed that the cumulative concentrations (μg L-1) of pharmaceuticals (mean ± standard error of the mean) were statistically more than two times significantly higher (p = 0.011) in South America (11.68 ± 5.29), Asia (9.97 ± 3.33), Africa (9.48 ± 2.81) and East Europe (8.09 ± 4.35) than in high-income regions (2.58 ± 0.48). Maximum cumulative concentrations of pharmaceuticals (μg L-1) decreased in the order; Asia (70.7) had the highest value followed by South America (68.8), Africa (51.3), East Europe (32.0) and high-income regions (17.1) had the least concentration. The corresponding human intake via ingestion of untreated river water was also significantly higher in low- and middle-income regions than in their high-income counterparts. For each region, the daily intake of pharmaceuticals was highest in infants, followed by children and then adults. A critique of the human health hazards, including toxicokinetics and toxicodynamics of EOCs is presented. Emerging health hazards of EOCs in DWS include; (1) long-term latent and intergenerational effects, (2) the interactive health effects of EOC mixtures, (3) the challenges of multifinality and equifinality, and (4) the Developmental Origins of Health and Disease hypothesis. Finally, research needs on human health hazards of EOCs in DWS are presented.

Emerging organic contaminants in the soil-plant-receptor continuum: transport, fate, health risks, and removal mechanisms

There is a lack of comprehensive reviews tracking emerging organic contaminants (EOCs) within the soil-plant continuum using the source-pathway-receptor-impact-mitigation (SPRIM) framework. Therefore, this review examines existing literature to gain insights into the occurrence, behaviour, fate, health hazards, and strategies for mitigating EOCs within the soil-plant system. EOCs identified in the soil-plant system encompass endocrine-disrupting chemicals, surfactants, pharmaceuticals, personal care products, plasticizers, gasoline additives, flame retardants, and per- and poly-fluoroalkyl substances (PFAS). Sources of EOCs in the soil-plant system include the land application of biosolids, wastewater, and solid wastes rich in EOCs. However, less-studied sources encompass plastics and atmospheric deposition. EOCs are transported from their sources to the soil-plant system and other receptors through human activities, wind-driven processes, and hydrological pathways. The behaviour, persistence, and fate of EOCs within the soil-plant system are discussed, including sorption, degradation, phase partitioning, (bio)transformation, biouptake, translocation, and bioaccumulation in plants. Factors governing the behaviour, persistence, and fate of EOCs in the soil-plant system include pH, redox potential, texture, temperature, and soil organic matter content. The review also discusses the environmental receptors of EOCs, including their exchange with other environmental compartments (aquatic and atmospheric), and interactions with soil organisms. The ecological health risks, human exposure via inhalation of particulate matter and consumption of contaminated food, and hazards associated with various EOCs in the soil-plant system are discussed. Various mitigation measures including removal technologies of EOCs in the soil are discussed. Finally, future research directions are presented.

The soil-microbe-plant resistome: A focus on the source-pathway-receptor continuum

The One World, One Health concept implies that antibiotic resistance (AR) in the soil-microbe-plant resistome is intricately linked to the human resistome. However, the literature is mainly confined to sources and types of AR in soils or microbes, but comprehensive reviews tracking AR in the soil-microbe-plant resistome are limited. The present review applies the source-pathway-receptor concept to understand the sources, behaviour, and health hazards of the soil-microbe-plant resistome. The results showed that the soil-microbe-plant system harbours various antibiotic-resistance genes (ARGs), antibiotic-resistant bacteria (ARB), and mobile genetic elements (MGEs). Anthropogenic sources and drivers include soil application of solid waste, wastewater, biosolids, and industrial waste. Water-, wind-, and human-driven processes and horizontal gene transfer circulate AR in the soil-microbe-plant resistome. The AR in bulk soil, soil components that include soil microorganisms, soil meso- and macro-organisms, and possible mechanisms of AR transfer to soil components and ultimately to plants are discussed. The health risks of the soil-microbe-plant resistome are less studied, but potential impacts include (1) the transfer of AR to previously susceptible organisms and other resistomes, including the human resistome. Overall, the study tracks the behaviour and health risks of AR in the soil-plant system. Future research should focus on (1) ecological risks of AR at different levels of biological organization, (2) partitioning of AR among various phases of the soil-plant system, (3) physico-chemical parameters controlling the fate of AR, and (4) increasing research from low-income regions particularly Africa as most of the available literature is from developed countries.

The pit latrine paradox in low-income settings: A sanitation technology of choice or a pollution hotspot?

Pit latrines are widely promoted to improve sanitation in low-income settings, but their pollution and health risks receive cursory attention. The present narrative review presents the pit latrine paradox; (1) the pit latrine is considered a sanitation technology of choice to safeguard human health, and (2) conversely, pit latrines are pollution and health risk hotspots. Evidence shows that the pit latrine is a 'catch-all' receptacle for household disposal of hazardous waste, including; (1) medical wastes (COVID-19 PPE, pharmaceuticals, placenta, used condoms), (2) pesticides and pesticide containers, (3) menstrual hygiene wastes (e.g., sanitary pads), and (4) electronic wastes (batteries). Pit latrines serve as hotspot reservoirs that receive, harbour, and then transmit the following into the environment; (1) conventional contaminants (nitrates, phosphates, pesticides), (2) emerging contaminants (pharmaceuticals and personal care products, antibiotic resistance), and (3) indicator organisms, and human bacterial and viral pathogens, and disease vectors (rodents, houseflies, bats). As greenhouse gas emission hotspots, pit latrines contribute 3.3 to 9.4 Tg/year of methane, but this could be an under-estimation. Contaminants in pit latrines may migrate into surface water, and groundwater systems serving as drinking water sources and pose human health risks. In turn, this culminates into the pit latrine-groundwater-human continuum or connectivity, mediated via water and contaminant migration. Human health risks of pit latrines, a critique of current evidence, and current and emerging mitigation measures are presented, including isolation distance, hydraulic liners/ barriers, ecological sanitation, and the concept of a circular bioeconomy. Finally, future research directions on the epidemiology and fate of contaminants in pit latrines are presented. The pit latrine paradox is not meant to downplay pit latrines' role or promote open defaecation. Rather, it seeks to stimulate discussion and research to refine the technology to enhance its functionality while mitigating pollution and health risks.