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Organic pollutants are potential hazards for human health and are pivotal contributors to ecological imbalances. The spectrum of chemicals in research on organic pollutants has continually evolved, which is influenced by industrial advancements, scientific breakthroughs, and regulatory frameworks. A comprehensive analysis of 30 review articles on organic pollutants published during 2019-2023 in Critical Reviews in Environmental Science and Technology (CREST) provides good perspectives on the trajectory of organic pollutants in the environment. This synthesis delineates the recent advancements in two domains: (1) innovative monitoring technologies (sensor, extraction method, bio-indicator, and radioactive tracer); and (2) fate and transport, and risk assessment of organic pollutants. However, research on organic pollutants needs better monitoring techniques, matrix-related transformation methodologies, and realistic risk assessment tools. The development of novel strategies to monitor and manage organic pollutants, coupled with evaluations of ecosystem impacts under field conditions, is paramount. [ABSTRACT FROM AUTHOR]

Phytohormones, including auxin, abscisic acid, gibberellic acid, ethylene, cytokinin, brassinosteroids, salicylic acid, and jasmonic acid, provide beneficial effects for plants against metal(loid) toxicity. However, their mechanisms in alleviating metal(loid) toxicity in plants have not been fully understood. Here, we summarize phytohormone-mediated detoxification mechanisms of metal(loid)s in plants, including As, Cd, Cr, Hg, and Pb. First, we discussed the functions of phytohormones on plant growth and nutrient uptake, and the effects of metal(loid)s on plant growth and hormone contents. We then discussed the underlying mechanisms of selected phytohormones in alleviating metal(loid) toxicity in plants. Those phytohormones protect plants against metal(loid) toxicity mainly by enhancing plant growth, increasing antioxidant capacity, promoting cell wall synthesis and nutrient uptake, and decreasing metal(loid) accumulation. This review highlights the beneficial roles of phytohormones in reducing plant metal(loid) uptake and in enhancing crop yields, which helps to improve crop production and food safety. [ABSTRACT FROM AUTHOR]

Biological remediation including bioremediation and phytoremediation has been used to remediate contaminated sites due to their cost-effectiveness, energy conservation, and environmental friendliness. There are 24 articles in Critical Reviews in Environmental Science and Technology (CREST) from 2018 to 2022 focusing on this topic. Bioremediation employs microorganisms to modify and/or degrade contaminants, while phytoremediation uses plants to remove, contain, and/or change contaminants. They cover different contaminants including traditional (nutrients, petroleum hydrocarbons, organo-pesticides, plastics, and heavy metals such as Cd, Cr, Pb and U) and emerging contaminants (pharmaceutical and personal care products, and perfluoroalkyl and polyfluoroalkyl substances). However, these remediation technologies have limitations in applications including lengthy periods, environmental sensitivity, nutrient deficiency and contaminant toxicity. Therefore, improvement strategies including immobilization of microbial/microalgal cells, construction of microbial/microalgal consortia, and use of amendments have been employed to overcome its drawbacks. Further studies should focus on cost-effective strategies to enhance the efficiency of biological remediation and their environmental adaptability, especially under extreme environments and with emerging contaminants. Microbes, microalgae and plants with good contaminant removal capability should be coupled with engineering practices based on their interactive mechanisms among bio-association and contaminants at molecular levels. [ABSTRACT FROM AUTHOR]

The biogeochemical transformations and biological effects of metalloids arsenic (As) and selenium (Se) in the environment has been extensively explored during the last decade, mainly owing to their ubiquitous distribution in the environment and their toxicity to biota. Here, we summarized recent research progress regarding As and Se in plant-soil-human ecosystem based on 17 publications in Critical Reviews in Environmental Science and Technology (CREST) during 2018-2021. The topics include: 1) organic As transformation in the environment and inorganic As uptake by plants (4 publications), 2) Se uptake by plants and its interactions with toxic metals in plants (6 publications), 3) As bioaccessibility and remediation of As-contaminated soils (4 publications), and 4) As research across spatial and temporal scale (3 publications). Specifically, the uptake, transformation, toxicity, bioaccessibility of As/Se in the plant-soil-human ecosystem together with pollution control measures are summarized. Future studies should focus on better understanding the cycling and biogeochemistry of As/Se in the environment, further decoding their environmental effects from the One Health perspective. [ABSTRACT FROM AUTHOR]

Soil plays an important role in controlling the biogeochemical cycling of nutrients and contaminants in the environment. Reliable analytical techniques are critical to better understand their transformation in soils. Diffusive Gradients in Thin-films technique (DGT) is one of such techniques, which has become increasingly popular in soil research since 1998. Undeniably, DGT attracts increasing attentions from multidisciplinary researchers worldwide. This is mainly due to its inherent merits, including ease of use, in situ measurement, and biomimetic applications. Further, four important aspects of DGT applications in soil research were summarized. They include: 1) chemical speciation, 2) bioavailability measurement, 3) desorption kinetic modeling, and 4) interfacial process mapping of nutrients and contaminants, with main focus on the progresses achieved during the past five years. In short, DGT is effective in studying the biochemical behaviors of nutrients (e.g., phosphate and nitrate), trace elements (e.g., Cd, Ni, Zn, Cu, Pb, and As), and polar organic compounds (e.g., antibiotics, pesticides, and bisphenols) in soils. Toward the end, we proposed several aspects of applying DGT as a versatile tool in soil research. [ABSTRACT FROM AUTHOR]

Animal bioassays have been developed to estimate oral relative bioavailability (RBA) of metals in soil, dust, or food for accurate health risk assessment. However, the comparability in RBA estimates from different labs remains largely unclear. Using 12 soil and soil-like standard reference materials (SRMs), this study investigated variability in lead (Pb) and arsenic (As) RBA estimates employing a mouse bioassay in 3 labs at Nanjing University, University of Jinan, and Shandong Normal University. Two performances of the bioassay at Nanjing University in 2019 and 2020 showed reproducible Pb and As RBA estimates, but increasing the number of mouse replicates in 2020 produced more precise RBA measurements. Although there were inter-lab variations in diet consumption rate and metal accumulation in mouse liver and kidneys following SRM ingestion due to differences in diet composition, bioassays at 3 labs in 2019 yielded overall similar Pb and As RBA estimates for the 12 SRMs with strong linear correlations between each 2 of the 3 labs for Pb (R2 = 0.95–0.98 and slope = 0.85–1.02) and As RBA outcomes (R2 = 0.46–0.86 and slope = 0.56–0.79). The consistency in RBA estimates was attributed to the relative nature of the final bioavailability outcome, which might overcome the inter-lab variation in diet consumption and metal uptake in mice. These results increased the confidence of use of mouse bioassays in bioavailability studies. [ABSTRACT FROM AUTHOR]

Widespread usage of nanotechnology has increased the release of metallic nanoparticles (MNPs) into the environment, which are mostly engineered. Agricultural soil is one of the most important sinks for MNPs. While numerous studies have focused on understanding the phytotoxicity of MNPs, and the extent and pathways of their accumulation in plants, the impacts of MNPs on soil health are only gaining attention recently. A comprehensive review summarizing the interactions of MNPs with soil is yet available. This review aims to fill the gap by evaluating the impacts of common MNPs on soil properties. Specifically, we examined the effects of MNPs on soil physical properties, the availability of plant nutrients and heavy metals from the perspective of food safety and security, as well as soil microbial ecology and microbial community associated with nutrient and carbon cycling. We underscored the impacts of environmental transformation of MNPs on soil health. Compared with soil physical and chemical properties, biological parameters of soil health are more susceptible to the impact of MNPs. Overall, the effects of MNPs and their transformed products on soil health vary with soils, MNPs, and exposure duration and dosage. [ABSTRACT FROM AUTHOR]

Arsenic (As) is a carcinogen and it is ubiquitous in the environment. Its accumulation in plants can enter the food chain, thereby causing adverse impacts on human health. Based on studies using Xenopus oocytes, engineered microbes, and model plants, aquaporins play key roles in arsenite (AsIII) passage across the cell membrane. Herein, we summarized the roles of aquaporins in AsIII uptake, transport, and accumulation. The coupling action between polar-localized aquaporins and positive transporters probably explains the efficient As transport mediated by bi-directional channels. The expression of aquaporins is regulated at both transcriptional and post-transcriptional levels via microRNAs. However, in response to As, the proteins can be modified through phosphorylation and be degraded via the ubiquitin 26S proteasome system. Further, a proposed model comprising reactive oxygen species, Ca, Ca-dependent kinases, and transcriptional factors is constructed to reveal the signaling pathways and aquaporins' responses to As in model plants. We also provided strategies to identify and investigate putative aquaporins in plants. Identification and modification of aquaporins' residues critical for their substrate selectivity, and optimization of their expression pattern by employing appropriate promoters can be employed to reduce As accumulation in crops. Based on the characteristics of their functions and expression patterns, it is promising to employ aquaporins for genetic-engineering of crops to reduce As content and increase food safety. [ABSTRACT FROM AUTHOR]

Arsenic is a ubiquitous metalloid found in the environment. Its chronic exposure is of global health concern as it causes lung, skin and bladder cancers, as well as non-cancer illness such as skin lesions, and cardiovascular and neurological diseases. While the environmental occurrence, fate, and toxicity of inorganic As has been well documented, limited research is available on organic As compounds. Organic As compounds often result from As metabolism in marine organisms, but they also enter the biosphere through anthropogenic activities including feed additives for livestock. Here, the state of knowledge on organic As is reviewed, encompassing their occurrence, toxicology and biotransformation including biosynthesis, methylation, and degradation. Knowledge gaps and possible research directions are identified, including metabolic pathways of synthesis and degradation, the impacts of metabolic transformations on toxicity and development of new analytical methods. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the environment and some exhibit carcinogenic and mutagenic toxicity. Three methods have been used for identification of PAHs sources in soils, including molecular diagnostic ratios, receptor models, and stable C isotopic signatures, with stable C isotopic ratios based on δ13C values being underutilized. Isotopic fractionation effects occur after environmental transportation of PAHs such as deposition and burial. This characteristic makes this method useful in source identification. Here, we provided a comprehensive review of tracing sources of soil PAHs using stable C isotopic fingerprinting technique. Fractionation of C isotopes occurs during formation and degradation processes of PAHs, making them useful tools to trace sources of PAHs in soils. The fundamentals of δ13C measurement and compound-specific isotopic analysis to trace sources of soil PAHs are summarized. Furthermore, for the first time, the biogeochemical cycle and contamination source evaluation based on δ13C signatures for soil PAHs are proposed. In addition, radioactive C isotope and stable H isotope ratios of PAHs are also briefly introduced as supplementary techniques. In short, these methods offer much promise, but still need work to fill in knowledge gaps. Establishing a C isotopic signature database to expand the utilization of this technique for tracing PAHs in soils is needed. [ABSTRACT FROM AUTHOR]

Wide application of nanoparticles (NPs) in consumer products over the last decade has increased their flux in the environment. This paper provides comprehensive review on the biocatalytic production pathways, transformations, and toxicity to human and other organisms of important NPs. Plants, algae, fungi, and bacteria have been used for energy-efficient and nontoxic biocatalytic production of NPs. The process is simple, serving as an alternative to the more popular physicochemical methods. NPs go through significant physicochemical transformation in the environment. Ionic strength, pH, and NPs’ surface potential strongly influence their stability and aggregation. Their transformations are linked to their bioavailability and aging including surface coatings and dissolved organic carbon effects. In addition, nanotoxicity has been a major global concern as NPs are toxic to organisms due to their cytotoxicity and genotoxicity. The stability and transformation of NPs in environment influence their short- and long-term toxicity. Release of free metal ions, dissolution-enhanced toxicity, and direct intercalation with biological targets are studied the most. Their toxicity to ecological receptors and organisms are linked to oxidative stress by generation of reactive oxygen species. Moreover, NPs toxicity depends on their physicochemical alterations. Inherent and acquired properties have potential to alter toxicity of NPs. Thus achieving safe nanotechnology and minimizing their adverse impact is important to protect the health of humans as well as the environment. [ABSTRACT FROM AUTHOR]

To better understand the environmental impact of lead (Pb) in shooting range soils, Pb levels in three berm soils were characterized via size distribution, total Pb concentration, water-soluble Pb, sequential extraction and X-ray diffraction (XRD). About 60% of the mid-berm soils of ranges-G and -O existed in grain sizes between 0.5 and 0.25 mm (medium sand) while range-L was most abundant in the 0.25 - 0.106 mm (fine sand) size fraction. All three range soils had the most accumulation of lead (60 - 70%) in the very coarse sand size (2.0 - 1.0 mm). In ranges-G and -L, the index shows a decreasing Pb enrichment with decreasing particle size, which may be a result of bullet fragmentation and abrasion in shooting range soils. Sequential extractions reveal that ranges-G and -L had the highest proportion of Pb bound to organic matter while range-O was dominated by the carbonate-bound fraction. However, a substantial proportion (one-third) of Pb in soil from the three shooting ranges was associated with carbonates. The XRD result revealed the dominance of carbonates in range-O soil, calcite in range-G soil and metallic lead in ranges-G and -O soil. The conversion of metallic lead to carbonates may be a mechanism for natural attenuation of lead in shooting range soils. Implications for remediation of shooting range soils are further discussed. [ABSTRACT FROM AUTHOR]

Colloid transport in subsurface has received considerable attention recently because mobile colloids can facilitate the transport of heavy metals in soils to contaminate groundwater. Many studies on colloid mobility in the subsurface consider soils as well-defined porous media. Though similar in many aspects, soils are different from well-defined porous media. The authors emphasize the impacts of soil properties on soil-colloid deposition, release, and association with heavy metals to provide an overview of colloidal dynamics in natural soils. The electrical double layer and Derjaguin-Landau-Verwey-Overbeek (DVLO) theories are summarized in Section II as theoretical bases for further discussions of colloid dynamics in soils, and their interactions with heavy metals. After discussions of theory developments and experimental results on the characteristics of soil colloids in Section III and soil porous media in Section IV, the authors compares the deposition of colloidal particles in well-defined porous media with that in natural soils in Section V. In Section VI, processes that affect colloid release in soils are summarized and theories of ion transfer processes in soils during colloid release are reviewed and discussed. Finally, the authors give a brief overview of the adsorption and precipitation of heavy metals to soil colloidal particles and their influences on colloid surface charge development in Section VII. The authors conclude with remarks on the importance of colloid deposition and release in soils and their association with heavy metals. [ABSTRACT FROM AUTHOR]

Pot experiments were conducted on cole (Brassica) grown in soils jointly treated with traces of two heavy metals cadmium (Cd) and zinc (Zn). As the concentration of heavy metals in the soil increased, the uptake of these metals by the plants rose. However, the ratio of heavy metal concentration in soil to uptake by plants increased at a slower rate. Bioavailability of heavy metals considered between the roots and soil using non-linear regressions was shown to be statistically significant. Similarly, the bioavailability of these two heavy metals between leaves and roots using a linear regression was also statistically significant. The bioconcentration factors (BCFs) for Cd and Zn were 0.282 and 4.289, respectively. Significant variation of BCF with the heavy metal bioavailability in soil was noted from non-linear models. The transfer factors (TFs) were 4.49 for Cd and 1.39 for Zn. The Zn concentration in leaves under all treatments did not exceed threshold set standards, but Cd levels exceeded these standards when the concentration of Cd in the soil was more than 1.92 mg kg-1 dry weight (dw). Data indicate that cole (Brassica) is not a suitable crop for oasis soils because of plant contamination with heavy metals, especially Cd. [ABSTRACT FROM AUTHOR]

This greenhouse study examined the root characteristics (biomass, length, area, and diameter) and root uptake efficiency of Pteris vittata, an arsenic (As) hyperaccumulator and Nephrolepis exaltata, not an As hyperaccumulator, in relation to plant uptake of As and nutrients in an As-contaminated and a control soil. After 8 weeks of growth, on a per plant basis, P. vittata accumulated 7.3-8.8 g of biomass and removed 2.51 mg of As from the As-contaminated soil compared to 2.4-2.7 g of biomass and 0.09 mg of As for N. exaltata. This was partially because P. vittata developed a more extensive root system, 2.4-3.8 times greater (biomass, length, and area), and possessed a greater proportion of fine roots than N. exaltata. In addition, the As root-uptake efficiency (defined as As concentrations in plant tissue per unit root) for fronds of P. vittata was 15-23 times greater than that of N. exaltata in both soils. Whereas N. exaltata removed phosphorus (P) more efficiently from the soils, P. vittata removed As more efficiently. The larger root biomass coupled with more efficient root-uptake systems for As may have contributed to As hyperaccumulation by P. vittata. [ABSTRACT FROM AUTHOR]

High volume application of wood ash as a soil amendment in forested areas may introduce toxic elements to these ecosystems. Column studies were conducted under unsaturated conditions to determine As and Cr leachability in wooed ash-amended soil columns. Three treatments were used in columns 1.8 cm diameter and 20 cm long: (a) ash alone, (b) ash mixed with topsoil at 900 Mg ha[sup-1] application rate, and (c) ash mixed with topsoil overlying a spodic horizon. Water, humic, fulvic, and a mixture of humic and fulvic acids were also used to leach ash in separate columns. Leachate concentrations of organic carbon, CI[sup-], As, and Cr and pH were determined. There was higher As and Cr leaching in the water-leached ash and soil-ash columns than in the acid-leached ash columns. The lower Cr leaching in HA-leached columns was due to the high reaction between Cr and HA. There was also lower dissolved organic carbon (DOC) leached in the acid-leached ash columns due to possible flocculation. Mixing ash with soil led to a higher increase in Cr leaching than As, which flocculated with DOC in the columns. High ash pH dissolved OC but high ionic strength led to DOC-oxyanion flocculation in this study. [ABSTRACT FROM AUTHOR]

Forest application of boiler ash is fast becoming a popular alternative to landfilling. Boiler ash is a good source of calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), manganese (Mn), and zinc (Zn), but it may potentially increase soil pH and electrical conductivity. A monitoring study was conducted to determine the changes in soil properties and the availability and leachability of nutrients following the application of large quantities of boiler ash in a sandy soil (with a spodic horizon). Two application rates (900 and 1800 Mg ha- 1) and two application methods (surface and subsurface) were used in a three-hectare area, which was divided into 15 subplots. Soil samples from different depths were collected over a period of 21 months. Soil pH increased from 5.6 to above 9 and the electrical conductivity increased by up to 2 orders in all plots compared to the controls. The high alkalinity from the ash in the 1800 Mg ha- 1 rate depleted the spodic layer, and this was more pronounced in the subsurface treatments. Plant-available water was doubled to 12% in the 1800 Mg ha- 1 treatment and soil bulk density was reduced from 1500 kg m- 3 to 1200–1360 kg m- 3. Total and plant available macronutrients (Ca, Mg, K, and P) and micronutrients [iron (Fe), Mn, copper (Cu), and Zn)] increased substantially after ash application. Based on our study, it is highly recommended that ash application rates be lowered to agronomic rates, e.g., ∼10 Mg ha- 1, based on liming equivalence, to maximize the beneficial effects of boiler ash on soil. [ABSTRACT FROM AUTHOR]

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO 3 -HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n=267) compared to 7.63 mg As/kg for disturbed soils (n=181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were generally higher in south Florida than in north and central Florida, and associated with wet soils. Individual high arsenic sites were scattered throughout the state, but the most highly concentrated of these occurred in the Leon-Lee belt along the Ocala uplift district extending to the southwestern flatwoods district. Extrapolation of the data using a single arsenic value regardless of the taxonomic and geographical differences in soil arsenic distribution would underestimate potential arsenic contamination in upland soils. [ABSTRACT FROM AUTHOR]

Reports on issues discussed by a panel of academic, industry and regulatory scientists on the resolution of arsenic background concentrations in Florida. Anonymity regarding specific sample locations; Vertical sampling issues; Data evaluation; Censorship of data sets; Florida Legislature's order for the Florida Department of Environmental Protection to develop rules for site rehabilitation incorporating risk-based corrective action principles.