Emerging Contaminant Imidacloprid in Mediterranean Soils: The Risk of Accumulation Is Greater than the Risk of Leaching

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.

Low-molecular-weight organic acids-mediated transport of neonicotinoid pesticides through saturated soil porous media: Combined effects of the molecular structures of organic acids and the chemical properties of contaminants

Empirical information about the transport properties of neonicotinoid pesticides through the soil as affected by the ubiquitous low molecular weight organic acids (LMWOAs) is lacking. Herein, the impacts of three LMWOAs with different molecular structures, including citric acid, acetic acid, and malic acid, on the mobility characteristics of two typical neonicotinoid pesticides (Dinotefuran (DTF) and Nitenpyram (NTP)) were explored. Interestingly, under acidic conditions, different mechanisms were involved in transporting DTF and NTP by adding exogenous LMWOAs. Concretely, acetic acid and malic acid inhibited DTF transport, ascribed to the enhanced electrostatic attraction between DTF and porous media and the additional binding sites provided by the deposited LMWOAs. However, citric acid slightly enhanced DTF mobility due to the fact that the inhibitory effect was weakened by the steric hindrance effect induced by the deposited citric acid with a large molecular size. In comparison, all three LMWOAs promoted NTP transport at pH 5.0. Because the interaction between NTP with soil organic matter (e.g., via π-π stacking interaction) was masked by the LMWOAs coating on soil surfaces. Nevertheless, LMWOAs could promote the mobility of both neonicotinoid pesticides at pH 7.0 due to the steric hindrance effect caused by the deposited organic acids and the competitive retention between LMWOAs and pesticides for effective surface deposition sites of soil particles. Furthermore, the extent of the promotion effects of LMWOAs generally followed the order of citric acid > malic acid > acetic acid. This pattern was highly related to their molecular structures (e.g., number and type of functional groups and molecular size). Additionally, when the background solutions contained Ca2+, the bridging effect of cations also contributed to the transport-enhancement effects of LMWOAs. The findings provide valuable information about the mobility behaviors of neonicotinoid pesticides co-existing with LMWOAs in soil-water systems.

First emerging pollutants profile in groundwater of the volcanic active island of El Hierro (Canary Islands)

Emerging pollutants (EPs) are substances present in wastewater that have not been studied, previously, leading to ambiguity in regulations for their presence in water resources. Territories that are highly dependent on groundwater resources are at a high risk of suffering the consequences of EP contamination due to their dependence on good quality groundwater for agriculture, drinking, and other uses. A relevant example is El Hierro (Canary Islands), which was declared a biosphere reserve by the UNESCO in 2000 and is almost completely powered by renewable energies. Using high performance liquid chromatography-mass spectrometry, the concentrations of 70 EPs were assessed at 19 sampling points on El Hierro. The results indicated that no pesticides were present in groundwater; however, varied concentration levels of ultraviolet (UV) filters, UV stabilizers/blockers and pharmaceutically active compounds (PhACs) were found, with La Frontera being the most contaminated municipality. With regard to the different installation types, piezometers and wells were the ones showing the highest concentrations for most EPs. Interestingly, the depth of sampling correlated positively with EP concentration, and four different clusters virtually dividing the island into two areas could be identified based on the presence of each EP. More studies should be performed to ascertain why a few of the EPs showed considerably high concentrations at different depths. The results obtained highlight the need to, not only implement remediation measures once EPs have reached the soil and aquifers, but also to avoid their incorporation into the water cycle via homes, animal husbandry, agriculture, industry, and wastewater treatment plants (WWTPs).

Microcosm-omics centric investigation reveals elevated bacterial degradation of imidacloprid

Imidacloprid, a broad-spectrum insecticide, is widely used against aphids and other sucking insects. As a result, its toxic effect is becoming apparent in non-targeted organisms. In-situ bioremediation of residual insecticide from the environment utilizing efficient microbes would be helpful in reducing its load. In the present work, in-depth genomics, proteomics, bioinformatics, and metabolomics analyses were employed to reveal the potential of Sphingobacterium sp. InxBP1 for in-situ degradation of imidacloprid. The microcosm study revealed ∼79% degradation with first-order kinetics (k = 0.0726 day^-1). Genes capable of mediating oxidative degradation of imidacloprid and subsequent decarboxylation of intermediates were identified in the bacterial genome. Proteome analysis demonstrated significant overexpression of the enzymes coded by these genes. Bioinformatic analysis revealed significant affinity and binding of the identified enzymes for their respective substrates (the degradation pathway intermediates). The nitronate monooxygenase (K7A41 01745), amidohydrolase (K7A41 03835 and K7A41 07535), FAD-dependent monooxygenase (K7A41 12,275), and ABC transporter enzymes (K7A41 05325, and K7A41 05605) were found to be effective in facilitating the transport and intracellular degradation of imidacloprid. The metabolomic study identified the pathway intermediates and validated the proposed mechanism and functional role of the identified enzymes in degradation. Thus, the present investigation provides an efficient imidacloprid degrading bacterial species as evidenced by its genetic attributes which can be utilized or further improved to develop technologies for in-situ remediation.

The distribution and human health risk assessment of eight neonicotinoid residues in agricultural soils from four provinces, south China

The widespread use of neonicotinoid (neonic) insecticides in China's agricultural sector has led to high residual concentrations in the agroecosystem. Since soil is the primary source of direct pesticide exposure, soil contamination is a significant concern, particularly in regions with extensive agricultural production. This study aims to determine the spatial distribution of neonics in farmlands from four southern provinces that are home to China's crucial commercial grain bases. By combining eight neonics into imidacloprid-equivalent total neonics (IMI_RPF) using the relative potency factor method, the ecological risks to humans were also assessed. The results showed that imidacloprid had the highest detection rate (96%-100%), followed by thiamethoxam and clothianidin, which ranged from 44% to 64%. Maximum and average IMI_RPF values in soil samples from Zhejiang Province were 277.02 and 46.05 μg kg^-1 (dry weight), respectively. Guangdong (maximum = 191.62 μg kg^-1, mean = 39.70 μg kg^-1) and Jiangxi (maximum = 199.13 μg kg^-1, mean = 28.95 μg kg^-1) had comparable IMI_RPF while Jiangsu had the lowest level of total neonics, with a maximum of 86.07 μg kg^-1 and a mean of 19.49 μg kg^-1. A significant positive correlation between IMI_RPF and total organic carbon in soils was also found. The average daily doses of neonics from soil-borne exposure through food intake, soil ingestion, inhalation, and dermal contact calculated for adults and children in each province were all lower than the reference dose (RfD, 57 μg kg^-1 d^-1) of imidacloprid. However, the potential health risk to human health cannot be disregarded, given their increasing use and pervasiveness in the environment. Our results help to raise concerns about the safety of the agroecological environment under neonic exposure in the major agricultural provinces of southern China.