Ecotoxicity of chlorophenolic compounds depending on soil characteristics

Incorporation of carbon black into a sonogel matrix: improving antifouling properties of a conducting polymer ceramic nanocomposite

A new electrochemical sensor device has been developed through the modification of a polyaniline-silicon oxide network with carbon black (CB). Enhanced electrical conductivity and antifouling properties have been achieved due to the integration of this cheap nanomaterial into the bulk of the sensor. The structure of the developed material was characterized using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy techniques. Cyclic voltammetry was used to characterize electrochemically the Sonogel-Carbon/Carbon Black-PANI (SNG-C/CB-PANI) sensor device. In addition, differential pulse voltammetry was employed to evaluate the analytical response of the sensor towards sundry chlorophenols, common environmental hazards in aqueous ecosystems. The modified sensor material showed excellent antifouling properties, which led to a better electroanalytical performance than the one displayed with the bare sensor. Notably, a sensitivity of 5.48 × 10³ μA mM^-1 cm^-2 and a limit of detection of 0.83 μM were obtained in the determination of 4-chloro-3-methylphenol (PCMC) at a working potential of 0.78 V (vs. 3 M Ag/AgCl/KCl), along with proficient values of reproducibility and repeatability (relative standard deviation < 3%). Finally, the analysis of PCMC was carried out in multiple validated water samples using the synthesized SNG-C/CB-PANI sensor device, obtaining excellent results of recovery values (97-104%). The synergetic effect of polyaniline and carbon black leads to novel antifouling and electrocatalytic effects that improve the applicability of this sensor in sample analysis versus complex conventional devices.

Ecotoxicological risk assessment of pentachlorophenol, an emerging DBP to plants: evaluation of oxidative stress and antioxidant responses

Chlorophenols are not only noticed in an effluvium of industries but also can emerge from the water treatment plants for domestic supply which poses a high threat for crop production and human health. Therefore, research on their risks to ecosystem and human health via ecotoxicological tests to derivate permissible environmental contaminant concentrations is necessary. The chlorophenols produced in the course of chlorination of potable water is an outcome of natural carboxylic acids/organic material and those chlorophenols occurred as emerging disinfection byproducts (EDBPs). Among chlorophenols, pentachlorophenol (PCP) has been recently identified as one of the important EDBPs. The main objective was to evaluate the PCP-induced genotoxicity and the oxidative damage in two plant species, i.e., Allium cepa and Vigna radiata. Genotoxicity of PCP was examined at three selected concentrations based on EC₅₀ (half-maximal effective concentrations) values in both the plants along with the defense mechanism. EC₅₀ value for A. cepa and V. radiata was 0.7 mg/L and 35 mg/L. Root length inhibition, DNA laddering, lipid peroxidation, H₂O₂ content, and antioxidant enzymatic assays evaluated revealed a dose-dependent response. PCP influenced defense enzyme glutathione peroxidase (GPX) and ascorbate peroxidase (APX) action in both plants and showed deprivement of catalase (CAT) with the increase of PCP concentrations. PCP-invaded toxicity management by these plants implied that A. cepa is more sensitive than V. radiata regarding PCP-induced toxicity.

Biochar amendment improves crop production in problem soils: A review

Problem soils are referred to as those with poor physical, chemical, and biological properties that inhibit or prevent plant growth. These poor properties may be a result of soil formation processes but are largely due to inappropriate farming practices or anthropogenic pollution. The world has lost a third of its arable land due to erosion and pollution in the past 40 years. Thus, there is an urgent need for improving and remediating problem soils. As a novel multifunctional carbon material, biochar has been widely used as a soil amendment for improving soil quality. Previous reviews have summarized the characteristics of biochar, the interactions with various soil contaminants, and the effects on soil quality, soil productivity, and carbon sequestration. Relatively limited attention has been focused on the effects of biochar amendment on plant growth in problem soils. As a result, a comprehensive review of literature in the Web of Science was conducted with a focus on the effects of biochar amendment on plant growth in problems soils. The review is intended to present an overview about problem soils, biochars as functional materials for soil amendment, how amended biochars interact with soils, soil microbes, and plant roots in remediation of problem soil and improve plant growth. Additionally, existing knowledge gaps and future directions are discussed. Information gathered from this review suggests that biochar amendment is a viable way of improving the quality of problem soils and enhancing crop production. It is anticipated that further research on biochar amendment will increase our understanding on the interactions of biochar with components of problem soils, speed up our effort on soil remediation, and improve crop production in problem soils.

Extraction and quantification of chlorophenolate molecules in soils spiked with 2,4-dichlorophenol and 2,4,5-trichlorophenol

The compounds 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) are classified as priority pollutants, with potentially hazardous impacts on the environment. In soil, dissociation of the phenol group occurs, resulting in the simultaneous presence of neutral phenol and anionic phenolate. Although the toxicity of 2,4-DCP and 2,4,5-TCP to soil microbiota has been suggested to be mainly due to the phenolate anion, this hypothesis cannot be tested due to the lack of appropriate methods of extracting and quantifying the anionic form of these compounds (unlike the neutral form, which can be easily quantified). In this study, we developed a method that enables extraction and quantification of phenolate ions. The method could therefore be used to elucidate the processes that regulate the behaviour of chlorophenolic molecules in soil and to clarify the distribution and toxicity of these compounds in the edaphic environment. The proposed method uses saline solutions (CaCl₂, KCl and K₂SO₄) of low ionic strength to extract the chlorophenolate anion from soil, followed by sequential transformation of the anion from the aqueous solution to an organic solvent that enables subsequent identification and quantification of the molecule by gas chromatography. Two soils of contrasting pH were used to test whether the proposed method was practicable. The method enabled analysis of the distribution of the neutral and anionic forms of the chlorophenols in both types of soil considered and revealed the influence of soil pH in this distribution.

Antibiotic effects on seed germination and root development of tomato (Solanum lycopersicum L.)

Antibiotics are emerging pollutants released into the environment through wastewater and manure or effluents from livestock plants. Compared to the wide literature on the effects of antibiotics on the development of drug-resistant bacteria and on the adverse effects on animals and human beings, the effects on plants are less investigated. Here we evaluated the effects of four antibiotics (cloramphenicol: CAP, spiramycin: SPR, spectinomycin: SPT, vancomycin: VAN) belonging to different chemical groups, on seed germination and root development of tomato (Solanum lycopersicum L. cv. San Marzano). Specifically, seed germination and root elongation kinetics, as well as the number of mithotic figures in root apical meristem, were studied in relation to different concentrations of each antibiotic (0, 0.1, 1, 10, 100, 1000mgL^-1) for 10 and 7 days, respectively. Results showed that seed germination was not affected, but root development (root elongation kinetics and cell division) was impaired at concentrations from 10mgL^-1 (SPT) and 100mgL^-1 (CAP) to 1000mgL^-1 (SPR and VAN).

The effects of different types of crop straw on the transformation of pentachlorophenol in flooded paddy soil

The incorporation of various types of crop straw to agricultural soils has long been practiced to improve soil fertility. However, the effects of crop straw on the fate of organo-chlorine pesticides in flooded paddy soils are not well understood. The dechlorination of pentachlorophenol (PCP) in four vertical profiles (0-10, 10-20, 20-30, 30-50 mm depth) of two flooded paddy soils, a Plinthudult (Soil 1) and a Tropudult (Soil 2) was investigated following the application of four crop straws (rice, wheat, rape and Chinese milk vetch) to them. In all treatments, PCP dechlorination decreased with increasing soil depth. In the crop straw treatments, PCP was almost completely dechlorinated within 60 days, and rapidly transformed to 2,3,4,5-tetrachlorophenol, and further to 3,4,5-trichlorophenol. Further dechlorination of 3,4,5-trichlorophenol also occurred in all treatments except for the rape straw. It is possible that the NH₄⁺ and NO₃^- derived from the straw are responsible for the inhibition of the 3,4,5-trichlorophenol dechlorination. The reduction of Fe (III) and SO₄^2- increased following application of the crop straws. The RDA analysis indicated that the Fe (III) reducing bacteria might be involved in the ortho-dechlorination, while SO₄^2- reducing bacteria were involved in para- and meta-dechlorination of PCP. The complete detoxification of PCP depended upon both the crop straw type and soil properties.

Phytotoxicity of 15 common pharmaceuticals on the germination of Lactuca sativa and photosynthesis of Chlamydomonas reinhardtii

Pharmaceuticals reach terrestrial environments through the application of treated wastewaters and biosolids to agricultural soils. We have investigated the toxicity of 15 common pharmaceuticals, classified as nonsteroidal anti-inflammatory drugs (NSAIDs), blood lipid-lowering agents, β-blockers and antibiotics, in two photosynthetic organisms. Twelve pharmaceuticals caused inhibitory effects on the radicle and hypocotyl elongation of Lactuca sativa seeds. The EC50 values obtained were in the range of 170-5656 mg L-1 in the case of the radicle and 188-4558 mg L-1 for the hypocotyl. Propranolol was the most toxic drug for both root and hypocotyl elongation, followed by the NSAIDs, then gemfibrozil and tetracycline. Other effects, such as root necrosis, inhibition of root growth and curly hairs, were detected. However, even at the highest concentrations tested (3000 mg L-1), seed germination was not affected. NSAIDs decreased the photosynthetic yield of Chlamydomonas reinhardtii, but only salicylic acid showed EC50 values below 1000 mg L-1. The first effects detected at low concentrations, together with the concentrations found in environmental samples, indicate that the use of biosolids and wastewaters containing pharmaceuticals should be regulated and their compositions assessed in order to prevent medium- and long-term impacts on agricultural soils and crops.

Site-specific water quality criteria for aquatic ecosystems: A case study of pentachlorophenol for Tai Lake, China

Given the widely varying types of aquatic ecosystems and bioavailability of chemicals, it is important to develop site-specific water quality criteria (WQC) to ensure criteria are neither over- nor under-protective. In the study, using pentachlorophenol (PCP) as an example, several approaches to derive site-specific WQC were investigated, including the conventional species sensitivity distribution (SSD), weighted SSD based on the proportion of each trophic level, and water effect ratio (WER) method. When corrected to a pH of 7.8, the conventional SSD approach resulted in criteria maximum concentration (CMC) and criteria continuous concentration (CCC) of 18.11 and 1.74 μg/L, respectively. If SSD was weighted according to the current species composition in Tai Lake, the CMC and CCC were 32.81 and 4.48 μg/L, respectively. However, available data suggest that many sensitive species inhabiting Tai Lake during 1980s were disappeared. Considering the species composition of the healthier ecosystem in 1980s, the CMC and CCC were 10.99 and 0.38 μg/L, respectively, which provide more protective water quality standards. Water effect ratio (WER) was further used to correct for co-occurrence of other toxicants and factors affecting bioavailability of PCP. A final WER of 4.72 was applied to adjust the criteria derived by using the weighted SSD for the 1980s aquatic community, and the final CMC and CCC obtained were 51.87 and 1.79 μg/L, respectively, at a pH of 7.8. Water quality criteria derived using the 1980s species composition and adjusted with WER were deemed the most appropriate WQC for water management and aquatic life protection. Merits of the various approaches for developing WQC for protection of aquatic species were discussed.

Ecotoxicity of Cr, Cd, and Pb on two Mediterranean soils

Three potentially toxic elements [chromium (Cr), lead (Pb), and cadmium (Cd)] were tested to assess their effects on two soils of different properties and origin. The soils were a granitic soil (Haplic Arenosol), which meets the requirements of OECD ecotoxicity testing, and a calcareous soil (Calcaric Regosol) with properties often found in the Mediterranean areas. The metal concentrations used ranged from 0.001 to 5,000 mg kg(-1) soil. The effects on soil microbial activity and community composition (respirometry and polymerase chain reaction-denaturing gradient gel electrophoresis analysis), as well as the effects on plant germination and elongation (Lactuca sativa), were assessed. The toxicity of the soil water extracts was also evaluated by the growth inhibition of algal populations (Pseudokirschneriella subcapitata). Cr showed the highest level of toxicity to soil organisms in the assays performed because this element remains in soil as anionic form and is less retained by the soil solid matrix than Cd and Pb. The lowest observed-adverse effect level for Cr ranged from approximately 0.1 mg kg(-1) [substrate induced respiration (SIR) test for the granitic soil] to 10 mg kg(-1) (basal respiration and SIR tests for the calcareous soil). For Pb (SIR) and Cd (SIR and alga tests), these levels were approximately 100 mg kg(-1). Germination and algal tests showed higher sensitivity in Regosol soil than in Arenosol soil for Cr due to differences in the bioavailability between the soils. In the cases or areas where alkaline soils are abundant, these should also be considered in laboratory ecotoxicity testing to avoid underestimation of ecotoxicological risks.

Use of Cl and C isotopic fractionation to identify degradation and sources of polychlorinated phenols: mechanistic study and field application

The widespread use of chlorinated phenols (CPs) as a wood preservative has led to numerous contaminated sawmill sites. However, it remains challenging to assess the extent of in situ degradation of CPs. We evaluated the use of compound-specific chlorine and carbon isotope analysis (Cl- and C-CSIA) to assess CP biotransformation. In a laboratory system, we measured isotopic fractionation during oxidative 2,4,6-trichlorophenol dechlorination by representative soil enzymes (C. fumago chloroperoxidase, horseradish peroxidase, and laccase from T. versicolor). Using a mathematical model, the validity of the Rayleigh approach to evaluate apparent kinetic isotope effects (AKIE) was confirmed. A small but significant Cl-AKIE of 1.0022 ± 0.0006 was observed for all three enzymes, consistent with a reaction pathway via a cationic radical species. For carbon, a slight inverse isotope effect was observed (C-AKIE = 0.9945 ± 0.0019). This fractionation behavior is clearly distinguishable from reported reductive dechlorination mechanisms. Based on these results we then assessed degradation and apportioned different types of technical CP mixtures used at two former sawmill sites. To our knowledge, this is the first study that makes use of two-element CSIA to study sources and transformation of CPs in the environment.

Estimating the toxicity of the weak base carbendazim to the earthworm (Eisenia fetida) using in situ pore water concentrations in different soils

Both sorption by soil and uptake by organisms of ionizable organic pollutants depend on their speciation (i.e., neutral and ionized forms); thus, the bioavailability of ionizable organic pollutants is more complicated than that of neutral organic pollutants in soil. The toxicity of the weak base carbendazim to earthworms (Eisenia fetida) was estimated using Soxhlet extracted concentrations (C(SE)), an excess of water extracted concentrations (C(EEW)), ex situ pore water concentrations (C(EPW)) and in situ pore water concentrations (C(IPW)) in different soils. The results indicated that the median lethal concentrations (LC50) calculated from C(SE) ranged from 2.32 to 34.0 mg kg(-1) in the five tested soils and the coefficient of variation (CV) of LC50s was 69.8%. When the LC50 was calculated from the C(EEW), C(EPW) and C(IPW), the variability of the LC50 gradually became smaller in these soils, with the CVs of LC50s being 58.1%, 50.6% and 38.6% (for C(EEW), C(EPW) and C(IPW), respectively). However, the LC50 based on C(IPW) in strongly acidic soil (where carbendazim partially exists as ionized form) was significantly lower than in other soils, and the values of the LC50 calculated from the in situ pore water concentrations were approximately equal. The results indicated that the in situ pore water concentration could be used to estimate the toxicity of carbendazim in different soils especially in those soils where carbendazim exists in the neutral form.

The exposition of a calcareous Mediterranean soil to toxic concentrations of Cr, Cd and Pb produces changes in the microbiota mainly related to differential metal bioavailability

The involvement of the bacterial community of an agricultural Mediterranean calcareous soil in relation to several heavy metals has been studied in microcosms under controlled laboratory conditions. Soil samples were artificially polluted with Cr(VI), Cd(II) and Pb(II) at concentrations ranging from 0.1 to 5000 mg kg(-1) and incubated along 28 d. The lowest concentrations with significant effects in soil respirometry were 10 mg kg(-1) Cr and 1000 mg kg(-1) Cd and Pb. However, only treatments showing more than 40% inhibition of respirometric activity led to significant changes in bacterial composition, as indicated by PCR-DGGE analyses. Presumable Cr- and Cd-resistant bacteria were detected in polluted microcosms, but development of the microbiota was severely impaired at the highest amendments of both metals. Results also showed that bioavailability is an important factor determining the impact of the heavy metals assayed, and even an inverted potential toxicity ranking could be achieved if their soluble fraction is considered instead of the total concentration. Moreover, multiresistant bacteria were isolated from Cr-polluted soil microcosms, some of them showing the capacity to reduce Cr(VI) concentrations between 26% and 84% of the initial value. Potentially useful strains for bioremediation were related to Arthrobacter crystallopoietes, Stenotrophomonas maltophilia and several species of Bacillus.

Terrestrial ecotoxicity of short aliphatic protic ionic liquids

A study of the ecotoxicity of different short aliphatic protic ionic liquids (PILs) on terrestrial organisms was conducted. Tests performed within the present study include those assessing the effects of PILs on soil microbial functions (carbon and nitrogen mineralization) and terrestrial plants. The results show that the nominal lowest-observed-adverse-effect concentration (LOAEC) values were 5,000 mg/kg (dry soil) for the plant test in two species (Lolium perenne, Allium cepa), 1,000 mg/kg (dry soil) for the plant test in one species (Raphanus sativus), and 10,000 mg/kg (dry soil) for carbon and nitrogen microbial transformation tests (all concentrations are nominal). Most of the median effective concentration values (EC50) were above 1,000 mg/kg (dry soil). Based on the obtained results, these compounds can be described as nontoxic for soil microbiota and the analyzed plants, and potentially biodegradable in soils, as can be deduced from the respirometric experiment. The toxicity rises with the increase of complexity of the PILs molecule (branch and length of aliphatic chain) among the three PILs analyzed.