To better determine phytotoxicity thresholds for metals in the soil, studies should use actual field-contaminated soil samples rather than metal-spiked soil preparations. However, there are surprisingly few such data available for Cu phytotoxicity in field-contaminated soils. Moreover, these studies differ from each other with regards to soil characteristics and experimental setups. This study aimed at more accurately estimating Cu phytotoxicity thresholds using field-collected agricultural soils (Entisols) from areas exposed to contamination from Cu mining. For this purpose, the exposure to Cu was assessed by measuring total soil Cu, soluble Cu, free Cu2+ activity, and Cu in the plant aerial tissues. On the other hand, two bioassay durations (short-term and long-term), three plant species (Avena sativa L., Brassica rapa CrGC syn. Rbr, and Lolium perenne L.), and five biometric endpoints (shoot length and weight, root length and weight, and number of seed pods) were considered. Overall plant growth was best predicted by total Cu content of the soil. Despite some confounding factors, it was possible to determine EC10, EC25 and EC50 of total Cu in the soil. Brassica rapa was more sensitive than Avena sativa for all endpoints, while Lolium perenne was of intermediate sensitivity. For the short-term bioassay (21 days for all three species), the averaged EC10, EC25 and EC50 values of total soil Cu (in mg kg−1) were 356, 621, and 904, respectively. For the long-term bioassay (62 days for oat and 42 days for turnip), the averaged EC10, EC25 and EC50 values of total soil Cu (in mg kg−1) were 355, 513, and 688, respectively. The obtained results indicate that chronic test is a suitable method for assessing Cu phytotoxicity in field-contaminated soils.

The aim of this study was to assess the effect of temperature on the toxicity of fipronil toward earthworms (Eisenia andrei) in two Brazilian soils (Entisol and Oxisol) with contrasting textures. In the case of Entisol, the influence of soil moisture content on toxicity was also investigated. Earthworms were exposed for 56 days to soils spiked with increasing concentrations of fipronil (8.95, 19.48, 38.22, 155.61, and 237.81 mg kg⁻¹ for Entisol; 12.99, 27.94, 48.42, 204.67, and 374.29 mg kg⁻¹ for Oxisol) under scenarios with different combinations of temperature (20, 25 and 27 °C) and soil moisture content (60 and 30% of water holding capacity (WHC) for Entisol and 60% WHC for Oxisol). The number of juveniles produced was taken as the endpoint, and a risk assessment was performed based on the hazard quotient (HQ). In Entisol, at 60% WHC the fipronil toxicity decreased at 27 °C compared with the other temperatures tested (EC₅₀ = 52.58, 48.48, and 110 mg kg⁻¹ for 20, 25, and 27 °C, respectively). In the case of Oxisol at 60% WHC, the fipronil toxicity increased at 27 °C compared with other temperatures (EC₅₀ = 277.57, 312.87, and 39.89 mg kg⁻¹ at 20, 25, and 27 °C, respectively). An increase in fipronil toxicity was also observed with a decrease in soil moisture content in Entisol at 27 °C (EC₅₀ = 27.95 and 110 mg kg⁻¹ for 30% and 60% WHC, respectively). The risk of fipronil was only significant at 27 °C in Entisol and Oxisol with water contents of 30% and 60% WHC, respectively, revealing that higher temperatures are able to increase the risk of fipronil toxicity toward earthworms depending on soil type and soil moisture content. The results reported herein show that soil properties associated with climatic shifts could enhance the ecotoxicological effects and risk of fipronil for earthworms, depending on the type of soil.

We evaluated the toxicity and risk (via toxicity exposure ratio approach — TER) of the insecticide fipronil to collembolan’s growth and reproduction in three tropical soils, under increasing atmospheric temperatures. Chronic toxicity tests were performed with Folsomia candida in tropical artificial soil (TAS), oxisol, and entisol spiked with increasing concentrations of fipronil, at three room temperature scenarios: a standard (20 ± 2 °C), a tropical condition (25 ± 2 °C) and a global warming simulation (27 ± 2 °C). Temperatures influenced the fipronil effects on the species reproduction differently between soil types. In TAS and oxisol the highest toxicities (EC₅₀-based) were found at 27 °C (EC₅₀ TAS = 0.81, 0.70, 0.31 mg kg⁻¹; EC₅₀ OXISOL = 0.52, 0.54, 0.40 mg kg⁻¹; at 20, 25, and 27 °C, respectively). In entisol, the toxicity at 27 °C was lower compared to 25 and 20 °C (EC₅₀ ENTISOL = 0.33, 0.24, 0.12 mg kg⁻¹, respectively). Fipronil concentrations also increased the proportion of small juveniles (growth reduction) in all tested soils. However, this effect was greater (EC₁₀-based) at higher temperatures (25 and/or 27 °C), regardless of the soil type. TER approach revealed a significant risk of fipronil in entisol, regardless of the tested temperature, while in other soils the risk was found significant only at the higher temperatures (25 and 27 °C for TAS, and 27 °C for oxisol). These results indicate that exposures to fipronil at high temperatures (e.g., those resulting from climate change) can threaten F. candida populations, depending on the soil type.

Stabilization of sewage sludge (SS) prior to its land disposal may help control the mobility of SS-borne contaminants, particularly potentially toxic metals. We examined the effects of stabilized SS application on soil properties, biomass production, and phytoavailability of Cu and Zn to plants grown in two contrasting soils, Entisol and Aridisol. Stabilized SS mixtures were created by mixing SS in a 3-to-1 ratio with bentonite (B), sugar beet factory lime (SL), brick factory fly ash (BFA), rice straw (RS), water hyacinth (WH), and 50:50 mixture of RS and SL. Mixtures were applied at 50 Mg ha⁻¹, and Sorghum vulgare L. and Eurica sativa were grown in a pot experiment. All the amendments increased plant availability and uptake of both Cu and Zn compared to the unamended control. The application of stabilized SS increased dry plant biomass significantly and decreased DTPA-extractable elements compared to the non-stabilized SS treatment. We conclude that of the six amendments studied, especially sugar beet factory lime (SL) and bentonite (B), are promising for the stabilization of metal-contaminated biosolids and should be tested under field conditions.

This study aimed to evaluate the effects of untreated pig manure from diets incorporating growth-promoting supplements (antibiotics and Zn oxide) on the survival and reproduction of Eisenia andrei earthworms. The tested manures were obtained from four different groups of pigs fed with four different diets: CS, a diet based on corn and soymeal; TR, a diet based on corn, soymeal, and ground wheat (15%); CSa, a diet based on corn and soymeal + 100 ppm of doxycycline + 50 ppm of colistin + 2500 ppm of Zn oxide; and TRa, a diet based on corn, soymeal, and ground wheat (15%) + 100 ppm of doxycycline + 50 ppm of colistin + 2500 ppm of Zn oxide. The study used two soils representative of the Southern region of Brazil (Oxisol and Entisol). In general, there were no significant differences between the different manures tested in each soil. However, there were differences in the toxicity manure on E. andrei between the soils, and the magnitude of this effect was dependent on the applied dose. In Oxisol, LC₅₀ values were higher than 80 m³ ha⁻¹, and EC₅₀ varied from 9 to 27 m³ ha⁻¹. In Entisol, the LC₅₀ values were below the lowest dose tested (< 25 m³ ha⁻¹), and EC₅₀ remained around 5 m³ ha⁻¹. It may be possible that the effects observed were attributed to an excess of nitrogen, copper, and zinc, promoted by the addition of the untreated manure and how these factors interacted with soil type.

The increasing emergence of antibiotic-resistant genes (ARGs) represents a global threat to human health. Land application of animal manure is known to contribute considerably to the propagation and dispersal of antibiotic resistance in agro-ecosystems. Yet, the primary determinants of the fate of the soil resistome remain obscure. In this study, a pot experiment was conducted to examine temporal changes in ARGs, mobile genetic elements (MGEs), and bacterial communities in a weakly developed loamy soil (an entisol known as calcareous purple soil) upon addition of pig or chicken manure. On the day of manure application, substantial increases in the diversity and relative abundance of ARGs were observed in soil amended with raw pig manure. At the same time, no obvious changes were observed for soil amended with chicken manure. Antibiotic resistance in pig manure-amended soils rapidly decreased over time to a level that was still higher than that of unamended soil at 100 days after manure application. The results of the Mantel test and Procrustes analysis indicated that ARG profiles in soil were significantly correlated with the structure of the bacterial phylogeny. Variation partitioning analysis further revealed that the bacterial community played a major role in regulating the temporal changes in ARGs in soil following manure application. Increased numbers and relative abundances of MGEs and their significant positive correlations with ARGs were observed, which suggest that a potential contribution from lateral gene transfer to the persistence and spread of ARGs should not be overlooked. Overall, our findings provide a better understanding of the mechanisms underlying the dynamics of ARGs in entisols following manure application and have practical implications for managing manure applications in entisols of the study area and other areas.

The poor adsorption capacity of sandy soils is one of the primary reasons of a high level of phosphorus (P) leaching. Silicon (Si)-rich soil amendments have the potential to improve the low absorption capacity of sandy soils for P. The objective of this study was to evaluate the ability of different Si-rich materials to regulate P adsorption and retention by sandy soils. Amorphous fine silica (FSS), calcium silicate (CaSiO₃), chemically pure CaCO₃, and two types of Ca-silicate slags from metal industry (Pro-Sil) and chemical industry (TS) were used in laboratory experiments being conducted with pure quartz sand and cultivated and virgin Entisols and Spodosols collected in the South Florida. The binding energy-related constants were evaluated for soils treated by Si-rich materials and then incubated during 2 months. The following row of tested materials on the increasing level of “affinity parameter” was determined: for virgin Spodosol, Pro-Sil < CaCO₃ < FSS< CaSiO₃ < TS; for cultivated Spodosol, FSS < Pro-Sil < CaCO₃< CaSiO₃ < TS; for virgin Entisol, Pro-Sil < CaSiO₃ < CaCO₃ < FSS < TS; and for cultivated Entisol, FSS < Pro-Sil < CaSiO₃ < CaCO₃ < TS. Chemical, physical, and physical-chemical mechanisms of increasing soil adsorption capacity are hypothesized and discussed to explain the results obtained. The conducted experiments have demonstrated high prospective of Si-rich materials for reduction of P leaching from cultivated sandy soils.

A hydrologically contained field study, to assess biochar (produced from mixed crop straws) influence upon soil hydraulic properties and dissolved organic carbon (DOC) leaching, was conducted on a loamy soil (entisol). The soil, noted for its low plant-available water and low soil organic matter, is the most important arable soil type in the upper reaches of the Yangtze River catchment, China. Pore size distribution characterization (by N₂ adsorption, mercury intrusion, and water retention) showed that the biochar had a tri-modal pore size distribution. This included pores with diameters in the range of 0.1–10 μm that can retain plant-available water. Comparison of soil water retention curves between the control (0) and the biochar plots (16 t ha⁻¹ on dry weight basis) demonstrated biochar amendment to increase soil water holding capacity. However, significant increases in DOC concentration of soil pore water in both the plough layer and the undisturbed subsoil layer were observed in the biochar-amended plots. An increased loss of DOC relative to the control was observed upon rainfall events. Measurements of excitation-emission matrix (EEM) fluorescence indicated the DOC increment originated primarily from the organic carbon pool in the soil that became more soluble following biochar incorporation.