Influence of water hardness on the bioavailability and toxicity of linear alkylbenzene sulphonate (LAS)

In the present work, the influence of Ca²⁺ concentration on the toxicity of single cut linear alkylbenzene sulfonate (LAS) homologues was studied. Precipitation boundary diagrams for each homologue were obtained, indicating turbid and clear zones depending on the LAS and Ca²⁺ concentrations. The separation between transparent and turbid zones is given by the so-called precipitation line. LAS toxicity to Daphnia magna was determined at concentrations close to this precipitation line. It was observed that when Ca(LAS)₂ precipitation progresses, LAS bioavailability decreases for test animals, and the toxicity diminishes even at high nominal LAS concentrations. According to the “free ion activity model” (FIAM), the toxicity of a given chemical compound is mainly due to the ionic species (Ca²⁺–LAS⁻) and not due to the precipitated molecule, Ca(LAS)₂. The significance of the present study is in connection with the assessment of LAS sorption/precipitation studies in soils and sediments, where in situ toxicity is strongly influenced by Ca²⁺/Mg²⁺ ions, according to the results presented in this work.     

Influence of linear alkylbenzene sulfonate (LAS) on the structure of Alphaproteobacteria,Actinobacteria, and Acidobacteria communities in a soil microcosm

Background, aim, and scope  

Linear alkylbenzene sulfonate (LAS) is the most used anionic surfactant in a worldwide scale and is considered a high-priority pollutant. LAS is regarded as a readily biodegradable product under aerobic conditions in aqueous media and is mostly removed in wastewater treatment plants, but an important fraction (20–25%) is immobilized in sewage sludge and persists under anoxic conditions. Due to the application of the sludge as a fertilizer, LAS reaches agricultural soil, and therefore, microbial toxicity tests have been widely used to evaluate the influence of LAS on soil microbial ecology. However, molecular-based community-level analyses have been seldom applied in studies regarding the effects of LAS on natural or engineered systems, and, to our knowledge, there are no reports of their use for such appraisals in agricultural soil. In this study, a microcosm system is used to evaluate the effects of a commercial mixture of LAS on the community structure of Alphaproteobacteria, Actinobacteria, and Acidobacteria in an agricultural soil.     

Chronic toxicity of sediment-associated linear alkylbenzene sulphonates (LAS) to freshwater benthic organisms

The toxicity of linear alkylbenzene sulphonates (LAS), to freshwater benthic organisms was assessed during exposure to spiked sediment. Lethal and sub-lethal end-points were monitored for two organisms (oligochaete Lumbriculus variegatus and nematode Caenorhabditis elegans). Results demonstrated relatively low toxicity (LOECs>100 mg/kg dry weight). No observed effect concentrations (NOECs) of 81 mg/kg dw (Lumbriculus) and 100 mg/kg dw (Caenorhabditis) were determined. For the oligochaete, no specific endpoint was particularly sensitive to LAS. For the nematode, egg production was the most sensitive endpoint. Significant degradation was measured over the 28-day duration of the Lumbriculus study, equating to a half-life of 20 days in sediment.     

Effect of metals on the adsorption and extractability of 14C-phenanthrene in soils

The fate of polycyclic aromatic hydrocarbons (PAHs) in contaminated soils may be affected by several environmental factors including the presence of co-contaminants. This study was conducted in order to assess the effect of metals on (i) the adsorption of 14C-phenanthrene in soils and (ii) its extractability and ability to form non-extractable residues. The first objective was accomplished using batch adsorption experiments with an uncontaminated agricultural soil spiked with the metals Cd, Cu, Pb, and Zn. Adsorption of phenanthrene was significantly higher after the addition of the metals (Kf = 21.48 vs. 8.55) and the desorption less readily reversible when compared to the unspiked soil. The extractability of phenanthrene was assessed with incubation (4 months, laboratory conditions) and microlysimeter experiments (6 months, natural climatic conditions) on three soils spiked with metals. All the soils were labelled with 14C-phenanthrene. The amount of extractable phenanthrene residues was significantly higher when the metals had been added to the soils. Nevertheless, the quantity of non-extractable residues was non-significantly different between the spiked and unspiked soils. The mechanism leading to increased adsorption and extractability of phenanthrene in the presence of metals is still unknown. In perspective, it would be interesting to assess the bioavailability of PAHs in the presence of metals in further experiments.     

Effects of a non-ionic surfactant (Tween-80) on the mineralization, metabolism and uptake of phenanthrene in wheat-solution-lava microcosm

Effects of a non-ionic surfactant (Tween-80) on the mineralization, metabolism and uptake of phenanthrene in wheat-solution-lava microcosm were studied using 14C-labeled phenanthrene. The mineralization and metabolism of phenanthrene were fast in such a system. At least 90% of the applied phenanthrene were transformed within 24 days. Only 0.3% of the applied 14C-activity were identified to be the parent phenanthrene. Most of the applied 14C-activity (70%) was recovered from wheat, in which ca. 70% were associated with wheat shoots (stems and leaves) and ca. 30% wheat roots. 33% and 20% of the applied 14C-activity had been constructed into wheat tissues of shoots and roots, respectively. The 14C-activity recovered in forms of CO2 and volatile organic chemicals (VOCs) was 12-16% and 4-5%, respectively. The major metabolites of phenanthrene were polar compounds (18% of the applied 14C) and only 2.1% were identified as non-polar metabolites. No phenanthrene was found in wheat shoots indicating that it could not be transported from roots to upper parts of the plant but in form of metabolites (mostly polar metabolites). Foliar uptake of 14C-activity via air in form of 14CO2 occurred. The presence of Tween-80 significantly enhanced the degradation of phenanthrene, which could be attributed to its increase of microbial activities in the system. Tween-80 also significantly (P < 0.05) reduced the phenanthrene level in wheat roots, which probably resulted from desorption of phenanthrene from root surface caused by the surfactant.     

Risk assessment of linear alkylbenzene sulphonates, LAS, in agricultural soil revisited: robust chronic toxicity tests for Folsomia candida (Collembola), Aporrectodea caliginosa (Oligochaeta) and Enchytraeus crypticus (Enchytraeidae)

To obtain robust data on the toxicity of LAS, tests with the collembolan Folsomia candida L., the oligochaetes Aporrectodea caliginosa Savigny (earthworm) and Enchytraeus crypticus Westheide and Graefe (enchytraeid) were performed in a sandy loam soil. Additionally limited tests with LAS spiked to sewage sludge, and subsequently mixed into soil, were performed. For the endpoint of interest, reproduction in soil, we found an EC10 of 205 mg LAS kg(-1) soil [8.6-401] [95% confidence limits] for F. candida and an EC10 of 46 mg LAS kg(-1) soil [13-80] for A. caliginosa after 28 days. E. crypticus was not affected by concentrations up to 120 mg LAS kg(-1) soil. When adding (low contaminated) non-spiked sludge to soil, high stimulation of reproduction was observed for E. crypticus and A. caliginosa but not for F. candida. We argue that this difference in stimulative response between the tested species is related to the difference in feeding behaviour. Sludge spiked with LAS did not significantly affect the reproduction of F. candida (fertility: number of juvenile offspring) and A. caliginosa (fecundity: number of cocoons) (dose equivalent to 181 g and 91 g LAS kg(-1) sludge, respectively). Significantly reduced reproduction was observed for E. crypticus (at 120 mg LAS kg(-1) soil+sludge corresponding to 72 g LAS kg(-1) sludge) compared to non-spiked sludge. The reproduction by E. crypticus was, however, comparable to the reproduction observed in the control soil without sludge. Compared to LAS directly spiked to soil, the reproductive output of organisms exposed to spiked sludge was either not significantly different (F. candida, E. crypticus) or significantly improved (A. caliginosa). More studies are needed in order to make firm conclusions on the potential effect of artificially contaminated sludge in soil systems.     

Impact of carbon nanomaterials on the behaviour of 14C-phenanthrene and 14C-benzo-[a] pyrene in soil

The impact of fullerene soot (FS), single-walled (SWCNTs) and multi-walled (MWCNTs) carbon nanotubes on the behaviour of two ¹⁴C-PAHs in sterile soil was investigated. Different concentrations of carbon nanomaterials (0, 0.05, 0.1 and 0.5%) were added to soil, and ¹⁴C-phenanthrene and ¹⁴C-benzo[a]pyrene extractability assessed over 80 d through dichloromethane (DCM) and hydroxypropyl-β-cyclodextrin (HPCD) shake extractions. Total ¹⁴C-PAH activity in soils was determined by combustion, and mineralisation of ¹⁴C-phenanthrene was monitored over 14 d, using a catabolically active pseudomonad inoculum. No significant loss of ¹⁴C-PAH-associated activity from CNM-amended soils was observed over the ‘aging’ period. CNMs had a significant impact on HPCD-extractability of ¹⁴C-PAHS; extractability decreased with increasing CNM concentration. Additionally, ¹⁴C-phenanthrene mineralisation was inhibited by the presence of CNMs at concentrations of ≥0.05%. Differences in overall extents of ¹⁴C-mineralisation were also apparent between CNM types. It is suggested the addition of CNMs to soil can reduce PAH extractability and bioaccessibility, with PAH sorption to CNMs influenced by CNM type and concentration.     

The influence of a NAPL on the loss and biodegradation of 14C-phenanthrene residues in two dissimilar soils

This study was carried out to assess the influence of diesel, applied over a log concentration range, on the loss and extractability of phenanthrene (measured as putative 14C-phenanthrene residues) in two different soils. The influence of diesel on the ability of a cyclodextrin based extraction method to predict the microbial bioavailability of 14C-residues was also assessed. An increase in loss of 14C-residues with increasing diesel concentration from 0 to 2000 mg kg-1 was generally observed with time in both soils. It is suggested that this trend is attributable to competitive sorption for soil sorption sites and to a lesser extent to displacement of 14C-residues from soil sorption sites by diesel resulting in greater compound availability and therefore greater loss by degradation via the actions of indigenous microorganisms. However, in the 20000 mg kg-1 diesel treatments of both soils, results indicated a delayed loss. It is suggested that this retarded loss was due to the formation of a discrete NAPL-phase into which 14C-phenanthrene residues partitioned, thereby decreasing their availability and as a consequence their degradation. Furthermore, it is suggested that nutrient limitation may have slowed down degradation rates as diesel concentrations increased. Comparison between cyclodextrin-extractability and microbial mineralisation supported the use of cyclodextrin to assess microbial bioavailability of 14C-residues after 50 d or more ageing up to diesel concentrations of 2000 mg kg-1. However, results suggested that at high diesel concentrations (specifically 20000 mg kg-1) co-extraction of 14C-phenanthrene residues may have occurred as a result of the combined solvation powers of both the cyclodextrin and the diesel. Furthermore, mineralisation of 14C-phenanthrene residues may have been affected by extreme nutrient limitation in this treatment.     

Portal absorption of 14C after ingestion of spiked milk with 14C-phenanthrene, 14C-benzo[a]pyrene or 14C-TCDD in growing pigs

Polycyclic aromatic hydrocarbons (PAHs) and dioxins are lipophilic organic pollutants occurring widely in the terrestrial environment. In order to study the PAHs and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) transfer in the food chain, pigs have been fed with milk mixed either with 14C-phenanthrene, with 14C-benzo[a]pyrene or with 14C-TCDD. The analysis of portal and arterial blood radioactivity showed that both PAHs and TCDD were absorbed with a maximum concentration at 4-6 h after milk ingestion. Then, the blood radioactivity decreased to reach background levels 24 h after milk ingestion. Furthermore, the portal and arterial blood radioactivities were higher for phenanthrene (even if the injected load was the lowest) than these of benzo[a]pyrene or these of TCDD, in agreement with their lipophilicity and water solubility difference. Main 14C absorption occurred during the 1-3 h time period after ingestion for 14C-phenanthrene and during the 3-6 h time period for 14C-benzo[a]pyrene and for 14C-TCDD. 14C portal absorption rate was high for 14C-phenanthrene (95%), it was close to 33% for 14C-benzo[a]pyrene and very low for 14C-TCDD (9%). These results indicate that the three studied molecules have a quite different behaviour during digestion and absorption. Phenanthrene is greatly absorbed and its absorption occurs via the blood system, whereas benzo[a]pyrene and TCDD are partly and weakly absorbed respectively. However these two molecules are mainly absorbed via the portal vein.     

Nonylphenols, nonylphenol-ethoxylates, linear alkylbenzenesulfonates (LAS) and bis (4-chlorophenyl)-sulfone in the German Bight of the North Sea.

Nonylphenols and nonylphenol-ethoxylates were detected in the water and sediment samples from the German Bight of the North Sea. Additionally bis (4-chlorophenyl)-sulfone and linear alkylbenzenesulfonates (LAS) were detected in marine waters. Proof of identification is given by comparison of spectral and chromatographic data from the compounds in sample extracts to those obtained from pure standards. In extracts obtained from water samples taken in 1990 and 1995 the concentrations of nonylphenols and bis-(4-chlorophenyl)-sulfone were compared for each year. The concentrations of nonylphenols in seawater varied from 0.7 to 4.4 ng/l while in the Elbe estuary about 33 ng/l were found. In water samples taken in 1998 nonylphenol-polyethoxylates could not be determined, whereas LAS concentrations of 30 ng/l were confirmed by HPLC-MS/MS. The concentrations of bis (4-chlorophenyl)-sulfone ranged from 0.18 to 2.2 ng/l. In sediment samples LAS concentrations of 39-109 ng/g dry weight were determined.     

Effect of aldicarb on the growth, respiration and (14C) - glucose metabolism of Axotobacter chroococcum BEIJ.

Aldicarb [2-methyl-2(methyl thio) propionaldehyde-O-methyl carbamoyl oxime], which forms the active ingredient of a systemic oximic carbamate insecticide, at 2 ppm level did not affect the in vitro growth and respiration of Azotobacter chroococcum Beij, while concentrations at 5 ppm and 10 ppm levels were inhibitory. The insecticide treatment at 10 ppm level suppressed the assimilation of (14C) - glucose in the whole cells and in the cellular constitutents viz., cold - TCA soluble, hot TCA soluble fractions and insoluble residue. However, the 14C - incorporation in the alcohol soluble and alcohol-ether soluble fractions was enhanced indicating that aldicarb considerably altered the glucose metabolism of the organism.     

Adsorption/desorption of linear alkylbenzenesulfonate (LAS) and azoproteins by/from activated sludge flocs

Our study investigated the adsorption/desorption by/from activated sludge flocs, dispersed in river water or in diluted wastewater, of organic compounds (C(11)-LAS, azoalbumin and azocasein) at concentrations relevant to environmental conditions. Activated sludge flocs, used as a model of biological aggregates, are characterized by a very heterogeneous matrix able to sorb the three organic compounds tested at 4 degrees C. The adsorbed amount of C(11)-LAS by activated sludge flocs was higher than that of azocasein or azoalbumin, as shown by the Freundlich parameters (K(ads)=8.6+/-1.7, 1.6+/-0.3 and 0.3+/-0.1 micromol(1-1/n)g(-1)l(1/n) for C(11)-LAS, azocasein and azoalbumin, respectively; n=3 sludges). C(11)-LAS sorption from activated sludge appeared to be partially reversible in river water, while a marked hysteresis phenomenon was observed for azocasein and azoalbumin, implying a low degree of reversibility in their exchange between activated sludge and river water. It has also been displayed that the conductivity variation of bulk water (comprised between 214 and 838 microS cm(-1)) exerted no dramatic effect on the C(11)-LAS desorption from activated sludge flocs, while a little effect of it on azocasein desorption was observed. Thus, biological aggregates as activated sludge flocs can serve as an intermediate carrier for C(11)-LAS, while it represents a sink for proteins.     

Effect of application of a herbicide propyzamide into the soil by study of mineralization of glucose 14C(U) and distribution of radioactivity in various fractions of the soil (laboratory and open field tests)

The effects of the herbicide PROPYZAMIDE are studied in laboratory and field conditions. The modifications involved are characterized by measurement of 14C-glucose mineralization and radioactivity incorporation into the soil fractions. In laboratory conditions, temperature and moisture are kept stable and the experiment is performed during less than 24 hours. In these conditions, Kerb 50 (commercial formulation of propyzamide) and the emulsifier (material used in propyzamide formulation) exert little effect on 14CO2 evolution. In field conditions, propyzamide andKerb 50 are applied once at two different doses: at field rate (1,5 kg/ha) and twentyfold this rate. Essays are duplicated. The herbicide (propyzamide in Celanol and Kerb 50) and the emulsifiers alone (Celanol and the material used in propyzamide formulation) are applied on the soil surface (application date: 3.02.81). Two weeks later and then every month during four months, samples are taken to the depth of about 5 cm (Propyzamide migrates very slowly in the first centimeters of the soil). The characterization experiment is performed on 10 g soil samples by 14C-glucose incubation at 28 degrees C during two hours. 14CO2 evolved is measured after incubation and acidification with HCl. Then radioactivity distribution in the soil is counted after chemical fractionation of soil. This distribution is about 10-16.5% as 14CO2, 22-37% in the acid-soluble fraction, 10-25% in the alkali-soluble fraction and 15-45% in the human fraction (measured as 14CO2 evolved after combustion). This distribution is little modified by the herbicides or the emulsifiers but its evolution is significantly related to environmental conditions (temperature). Nevertheless a few modifications are observed. They can be due to the herbicide propyzamide itself but the emulsifiers and the degradation products of propyzamide can also influence the measurement (After forty days in the soil, 70-95% of the starting active ingredient have disappeared). They can also be a result of the initial effects of the products (modification of the microflora and of the environment).     

In vitro biotransformation of surfactants in fish. Part I: linear alkylbenzene sulfonate (C12-LAS) and alcohol ethoxylate (C13EO8)

Developing regulatory activities (e.g., REACh, [DGEE. 2003. Directorates General Enterprise and Environment. The new EU chemicals legislation REACH. DG Enterprise, Brussels, Belgium. (http://www.europa.eu.int/comm/enterprise/reach/index_en.htm)]) will require bioaccumulation to be assessed for thousands of chemicals. Further, there is increasing pressure to reduce, refine or replace animal tests. Given this scenario, there is an urgent need to evaluate the feasibility of in vitro systems to supply data useful for bioaccumulation estimation. Subcellular and cellular hepatic systems were tested to determine the biotransformation of two surfactants: C12-2-LAS (2-phenyl dodecane p-sulfonate) and an alcohol ethoxylate C13EO8 (Octaethylene glycol monotridecyl ether). The subcellular systems tested were liver homogenates and microsomes from the common carp (Cyprinus carpio) and rainbow trout (Oncorhynchus mykiss). Cellular systems consisted of primary hepatocytes from the common carp (Cyprinus carpio) and PLHC-1 cells, hepatocarcinoma cells from the desert topminnow (Poeciliopsis lucida). All in vitro systems were exposed to radiolabeled test compounds and assayed for biotransformation using liquid scintillation and thin layer chromatographic methods. First-order kinetics were used to estimate rates of biotransformation. Bioconcentration of test materials in fish were predicted using an in vitro to in vivo metabolic rate extrapolation model linked to a mass-balance model commonly used to predict bioaccumulation in fish. Subcellular biotransformation rates for each of the surfactants were greatest with microsomes. Cellular loss rates exceeded subcellular rates, leading to lower predicted BCF values. Predicted BCFs corresponded closely to measured values in several fish species, verifying the utility of in vitro systems in refining Kow-only-based BCFs via the inclusion of biotransformation rates.     

Time study on the uptake of four different beta-blockers in garden cress (Lepidium sativum) as a model plant

Environmental Science and Pollution Research - The aim of this study was to investigate the uptake of four beta-blockers by the model plant Lepidium sativum (garden cress) and their possible...     

Modeling the mechanisms for uptake and translocation of dioxane in a soil-plant ecosystem with STELLA

Knowledge of mechanisms for uptake, translocation, and accumulation of soil contaminants in plants is essential to successful applications of the phytoremediation technique. Analysis and evaluation of these mechanisms would be greatly facilitated by the availability of a dynamic model that can predict soil contaminant uptake by roots, transport from roots through stems to leaves, and accumulation in plant during the transport process. In this study, a dynamic model for uptake and translocation of contaminants from a soil-plant ecosystem (UTCSP) was developed using the STELLA modeling tool. The structure of UTCSP consists of time-dependent simultaneous upward transport, accumulation, and transpiration of water and contaminants in the soil-plant-atmosphere continuum, which was driven by water potential gradients among soils, roots, stems, leaves, and atmosphere. The UTCSP model was calibrated using the experimental measurements and applied to predict phytoremediation of 1,4-dioxane from a sandy soil by a poplar tree. Simulation results showed that about 20% of 1,4-dioxane was removed from the soil by the poplar tree in 90 days. The simulations further revealed that while the mass of 1,4-dioxane in the poplar tree increased consecutively with time, the rates of water and 1,4-dioxane uptake and translocation in the roots, stems, and leaves have a typical diurnal distribution pattern: increasing during the day and decreasing during the night, resulting from daily variations of plant water potentials that were caused by leaf water transpiration. This study suggests that the UTCSP model is a useful tool for estimating phytoremediation of contaminants in the soil-plant ecosystems.     

Dynamics of PAH deposition, cycling and storage in a mixed-deciduous (Quercus-Fraxinus) woodland ecosystem

Estimates of standing biomass and fluxes of biomass in a mixed-deciduous woodland were derived, and used with results for concentrations of seven polycyclic aromatic hydrocarbons (PAHs) in different compartments of the woodland system to quantitatively assess some of the key fluxes and burdens of PAHs in this complex system. We quantified PAH burdens in air, in leaves of three deciduous tree species, in leaf litter and in soil, and uptake of PAHs by the tree leaves; PAH fluxes in litterfall, and deposition to the litter layer on the woodland floor during winter were calculated from these data. Air burdens exhibited marked seasonal variations for all compounds, with lowest values in summer when combustion-related emissions were low. Leaves did not accumulate large burdens of PAHs while on the trees and consequently, litterfall-associated fluxes of PAHs were small, representing only a fraction of the burdens in the litter layer to which they were deposited. Higher PAH burdens in air in winter, combined with the organic-matter-rich nature of the litter layer, are thought to be responsible for fluxes of PAHs to the litter layer in winter being 20-170 times the peak litterfall fluxes. The soil compartment was calculated to contain 25 years' worth of deposition of benzo[ghi]perylene, the most recalcitrant PAH in this study. Storage quotients for fluoranthene, pyrene, benzo[k]fluoranthene and benzo[a]pyrene burdens in soil represented 7-10 years' worth of deposition, while fluorene and phenanthrene storage in soil approached unity with inputs (1 and 3 years' worth of deposition, respectively). The relative importance of storage and loss processes was therefore closely related to the physico-chemical properties of the PAH, and is discussed in relation to the cycling of carbon in the woodland.     

Comparison of a mass balance and an ecosystem model approach when evaluating the carbon cycling in a lake ecosystem

Carbon budgets are frequently used in order to understand the pathways of organic matter-in ecosystems, and they also have an important function in the risk assessment of harmful substances. We compared two approaches, mass balance calculations and an ecosystem budget, to describe carbon processing in a shallow, oligotrophic hardwater lake. Both approaches come to the same main conclusion, namely that the lake is a net autotrophic ecosystem, in spite of its high dissolved organic carbon and low total phosphorus concentrations. However, there were several differences between the carbon budgets, e.g. in the rate of sedimentation and the air-water flux of CO2. The largest uncertainty in the mass balance is the contribution of emergent macrophytes to the carbon cycling of the lake, while the ecosystem budget is very sensitive towards the choice of conversion factors and literature values. While the mass balance calculations produced more robust results, the ecosystem budget gave valuable insights into the pathways of organic matter transfer in the ecosystem. We recommend that when using an ecosystem budget for the risk assessment of harmful substances, mass balance calculations should be performed in parallel in order to increase the robustness of the conclusions.