Alkylbenzene Sulphonate Research Articles

MBAS (Methylene Blue Active Substances) and LAS (Linear Alkylbenzene Sulphonates) in Mediterranean coastal aerosols: Sources and transport processes

Abstract Methylene Blue Active Substances (MBAS) and Linear Alkylbenzene Sulphonates (LAS) concentrations, together with organic carbon and ions were measured in atmospheric coastal aerosols in the NW Mediterranean Basin. Previous studies have suggested that the presence of surfactants in coastal aerosols may result in vegetation damage without specifically detecting or quantifying these surfactants. Coastal aerosols were collected at a remote site (Porquerolles Island-Var, France) and at a more anthropised site (San Rossore National Park-Tuscany, Italy). The chemical data were interpreted according to a comprehensive local meteorological analysis aiming to decipher the airborne source and transport processes of these classes of compounds. The LAS concentration (anthropogenic surfactants) was measured in the samples using LC-MS/MS, a specific analytical method. The values were compared with the MBAS concentration, determined by a non-specific analytical method. At Porquerolles, the MBAS concentration (103 ± 93 ng m −3 ) in the summer samples was significantly higher than in the winter samples. In contrast, LAS concentrations were rarely greater than in the blank filters. At San Rossore, the mean annual MBAS concentration (887 ± 473 ng m −3 in PM10) contributed about 10% to the total atmospheric particulate organic matter. LAS mean concentration in these same aerosol samples was 11.5 ± 10.5 ng m −3 . A similar MBAS (529 ± 454 ng m −3 ) – LAS (7.1 ± 4.1 ng m −3 LAS) ratio of ∼75 was measured in the fine (PM2.5) aerosol fraction. No linear correlation was found between MBAS and LAS concentrations. At San Rossore site the variation of LAS concentrations was studied on a daily basis over a year. The LAS concentrations in the coarse fraction (PM10–2.5) were higher during strong sea storm conditions, characterized by strong air flow coming from the sea sector. These events, occurring with more intensity in winter, promoted the formation of primary marine aerosols containing LAS from the sea surface microlayer. In contrast to LAS, MBAS concentrations in the coarse fraction peaked in summer. Therefore, different sources are suggested for the two classes of compounds. In summer, increased MBAS concentration could be an indicator of phytoplanktonic blows enriching the sea surface microlayer with biogenic surfactants. In winter, some spikes in MBAS concentrations in the coarse fraction could be related to LAS concentrations and sea storm events. Moreover, in the fine fraction MBAS have a large concentration maxima in winter, corresponding to air masses coming from polluted continental areas. It is concluded that MBAS concentration in the fine or the coarse fraction is not an appropriate surrogate measurement of LAS concentration in aerosols because of the significant contribution from other sources to the MBAS concentration.

Aquatic Risk Assessment of Alcohol Ethoxylates, Alcohol Ethoxysulphates and Linear Alkylbenzene Sulphonate used in Household Detergents

Abstract Exposure and effect assessments including risk characterisation of the surfactants alcohol ethoxylates, alcohol ethoxysulphates and linear alkylbenzene sulphonates used in household detergents were conducted. Predicted environmental concentrations were calculated by use of traditional methods and detailed transport and fate modelling. Predicted no effect concentrations were derived from the available information on the acute and chronic aquatic toxicity. Risk characterisation ratios were defined as the ratio of the predicted environmental concentration to the predicted no effect concentration. Risk characterisation ratios were calculated for fresh water and marine water and were below 1. This indicates that based on the methods employed in this study the use of alcohol ethoxylates, alcohol ethoxysulphates and linear alkylbenzene sulphonate in household detergents does not appear to present a risk to the aquatic environment.

Priority organic pollutants in the urban water cycle (Toulouse, France)

Application of the European Water Framework Directive requires Member States to have better understanding of the quality of surface waters in order to improve knowledge of priority pollutants. Xenobiotics in urban receiving waters are an emerging concern. This study proposes a screening campaign of nine molecular species of xenobiotics in a separated sewer system. Five sites were investigated over one year in Toulouse (France) using quantitative monitoring. For each sample, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, nonylphenols, diethelhexylphthalate, linear alkylbenzene sulphonates, methyl tert-butylether, total hydrocarbons, estradiol and ethinylestradiol were analysed. Ground, rain and roof collected water concentrations are similar to treated wastewater levels. Run-off water was the most polluted of the five types investigated, discharged into the aquatic environment. The wastewater treatment plant reduced xenobiotic concentrations by 66% before discharge into the environment. Regarding environmental quality standards, observed concentrations in waters were in compliance with standards. The results show that xenobiotic concentrations are variable over time and space in all urban water compartments.

Electrical Properties of Carbon Nanotubes Cement Composites for Monitoring Stress Conditions in Concrete Structures

Cement pastes reinforced with Multi-Walled carbon NanoTubes (MWNTs) are smart materials with piezoresistivity properties. Adding carbon nanotubes to the cement matrix, in fact, the electrical resistivity of cementitious composites changes with the stress conditions under static and dynamic loads. This particular behaviour can be used to evaluate the stress level in reinforced concrete structures, to monitor the traffic flow, to weigh vehicles. In this paper data on pressure-sensitive behaviour under compressive stress of cement pastes and mortars containing different percentages (from 0.0% to 1.0% vs. cement mass) of MWNTs are presented.In order to form a conductive network and enhancethe piezoresistive properties of cementitious mixtures, Carbon NanoTubes (CNTs) need to be efficiently dispersed in the cement matrix. Two different methods to disperse CNTsin the cement matrix were used. The first one uses a surfactant (Sodium Linear Alkyl Benzene Sulphonate - LAS): MWNTs were dispersed in a LAS aqueous solution,and thenmixed with cement and a defoamer (tributyl phosphate) to decrease the air bubble in MWNT filled cement-based composites. The second method consists in mixing CNTs with about 50% of the mixing water in a becker by means of a glass wand. Then, the solution is sonicated by an ultrasonic generator for 10 minutes. Finally, the sonicatedCNT-aqueous solution ismixed with cement (and sand for the mortars). The piezoresistivity properties of the cementitious mixtures manufactured with the two above mentioned CNTs dispersing methods will be compared.Experimental results show that the electrical resistance changes synchronously with the compressive stress levelsfor the specimens manufactured with both methods. Therefore, CNTs improve the pressure-sensitivity of cementitious composites. Moreover, the piezoresistive response is better for cementitious composites manufactured by using the surfactant agent to disperse CNTs. Data indicate that – thanks to the better dispersion of nanotubes promoted by the surfactant - the pressure-sensitivity properties of cement pastes can be achieved even by using a very low percentage of CNTS (0.1% vs. cement mass). These findings seem to indicate that self-sensing CNTs/cement composite can be produced. These smart materials have great potential and they could be used in the next future in concrete field for practical applications to monitor the stress level of reinforced concrete elements subjected to static, dynamic and impact loads. In particular, informations on actual stress existing under dynamic and impact loads could be improve design procedures in protective structures.

Occurrence of high-tonnage anionic surfactants in Spanish sewage sludge

Agricultural application has become the most widespread method of sewage sludge disposal, being the most economical outlet for sludge and also recycling beneficial plant nutrients and organic matter to soil for crop production. As a matter of fact, the European Sewage Sludge Directive 86/278/EEC seeks to encourage the disposal of sewage sludge in agriculture applications and regulate its use to prevent harmful effects on the soil environment. At the present time, the sewage sludge Directive is under revision and a possible cut-off limit for some organic chemicals may be implemented. Linear alkylbenzene sulphonate (LAS), the main synthetic anionic surfactant, has been included in the draft list of chemicals to be limited. The present research work deals with the monitoring of LAS and soap in Spanish sewage sludge. The average concentration of LAS found in anaerobic sewage sludge samples was 8.06 g/kg, higher than the average values for European sludge. Besides, it has been also found that more than 55% of Spanish anaerobic sludge would not fulfil the limit proposed by the 3rd European Working paper on sludge. As a consequence, the implementation of the limit for LAS would make the disposal of most Spanish biosolids for agricultural applications almost impossible. Regarding the mechanisms why anionic surfactants are found in sludge, two surfactants are compared: LAS and soap, both readily biodegraded in aerobic conditions. Irrespective of the anaerobic biodegradability of soap, its concentration found in sludge is higher than LAS (only anaerobically biodegradable under particular conditions). The relevance of anaerobic biodegradation to assure environmental protection is discussed for this case.

PHYSIOLOGICAL RESPONSES OF THE BROWN MUSSEL Perna perna (MOLLUSCA, BIVALVIA) EXPOSED TO THE ANIONIC SURFACTANT LINEAR ALKYLBENZENE SULPHONATE (LAS)

The effects of the Linear Alkylbenzene Sulphonate (LAS) were evaluated on the mussel Perna perna, using physiological and genotoxic biomarkers. The Micronuclei (MN) assay was used to estimate effects at nuclear level, whereas the physiological effects were evaluated by measuring the oxygen consumption and ammonia excretion rates. Significant effects were observed for the MN assay and the ammonia excretion rate, even in low concentrations. The oxygen consumption was not affected in the tested concentrations. For MN and ammonia excretion, the animals exposed to intermediate concentrations were not affected, but responded to the higher concentrations, indicating the existence of compensatory mechanisms at physiological level. However, parallel to this study other authors indicate the presence of progressive effects at the cellular level, suggesting that the organisms are not capable to recover of such increasing effects. Additionally, the results show that the levels of LAS observed for Brazilian coastal waters may chronically affect the biota.

Impact of carwash discharge on stormwater quality (Toulouse, France)

The contribution of discharge from carwashes to pollutant levels in stormwater was evaluated. Five carwashes and two outlets in the city of Toulouse (France) were selected. Water samples were collected from December 2006 to December 2007. Concentrations and loadings of classical water quality parameters (conductivity, pH, turbidity, chemical oxygen demand, nitrogen, phosphorus, ammonium, nitrate, suspended solid and volatile suspended solid) and five groups of organic compounds (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, lauryl alkyl benzene sulphonates, methyl tert-butyl ether and total hydrocarbons) were determined. The results suggest that the wastewater derived from carwashes was negligible compared to the volume and flow rates within the stormwater network. However, high concentrations of polycyclic aromatic hydrocarbons, phosphorus and lauryl alkyl benzene sulphonates in liquid waste from carwashes, and the impact of these pollutants on stormwater quality could not be neglected.

Synthesis and Application of the Cationic Lignin Amine Flocculant

Abstract Cationic lignin amine flocculants were obtained by the Mannich reaction of Kraft lignin with formaldehyde and polyamines. The cationic reaction products were tested as a flocculating agent by flocculation of reactive brilliant blue KN-R and linear alkylbenzene sulphonates in an aqueous system. The effects of flocculant dosage and pH on the flocculation performance are discussed in detail. The results indicate that under optimum conditions, the rate of eliminating reactive brilliant blue KN-R and linear alkylbenzene sulphonates from the water exceed 99% and 96% respectively, which illustrated that the cationic reaction products are extremely effective as flocculants for reactive brilliant blue KN-R and linear alkylbenzene sulphonates.

Degradation of 4-n-nonylphenol under nitrate reducing conditions

Nonylphenol (NP) is an endocrine disruptor present as a pollutant in river sediment. Biodegradation of NP can reduce its toxicological risk. As sediments are mainly anaerobic, degradation of linear (4-n-NP) and branched nonylphenol (tNP) was studied under methanogenic, sulphate reducing and denitrifying conditions in NP polluted river sediment. Anaerobic bioconversion was observed only for linear NP under denitrifying conditions. The microbial population involved herein was further studied by enrichment and molecular characterization. The largest change in diversity was observed between the enrichments of the third and fourth generation, and further enrichment did not affect the diversity. This implies that different microorganisms are involved in the degradation of 4-n-NP in the sediment. The major degrading bacteria were most closely related to denitrifying hexadecane degraders and linear alkyl benzene sulphonate (LAS) degraders. The molecular structures of alkanes and LAS are similar to the linear chain of 4-n-NP, this might indicate that the biodegradation of linear NP under denitrifying conditions starts at the nonyl chain. Initiation of anaerobic NP degradation was further tested using phenol as a structure analogue. Phenol was chosen instead of an aliphatic analogue, because phenol is the common structure present in all NP isomers while the structure of the aliphatic chain differs per isomer. Phenol was degraded in all cases, but did not affect the linear NP degradation under denitrifying conditions and did not initiate the degradation of tNP and linear NP under the other tested conditions.

Control of an Outbreak of Carbapenem-ResistantAcinetobacter baumanniiin Australia after Introduction of Environmental Cleaning with a Commercial Oxidizing Disinfectant

In the midst of an outbreak, carbapenem-resistant Acinetobacter baumannii was grown from samples of multiple environmental sites in an intensive care unit. A commercial oxidizing disinfectant (potassium peroxomonosulphate 50%, sodium alkyl benzene sulphonate 15%, and sulphamic acid 5%) was introduced throughout the intensive care unit, and its use coincided with cessation of the outbreak.

Conceptual analysis of the UASB/polishing pond system regarding the removal of surfactants, micropollutants and control of gaseous emissions

A conceptual and integrated analysis of the UASB/Polishing Pond system is presented in relation to the removal of specific constituents not normally covered in the pond's literature, namely surfactants (linear alkylbenzene sulphonate, LAS), micropollutants (phthalates and bisphenol A) and sulfide. Experimental studies carried out on a small full-scale UASB/PP system have shown limited overall removal efficiencies for some constituents (53% to 70% for phthalates and 50% for LAS), but excellent removal levels for bisphenol A (around 99%) and sulfide (no trace concentrations were detected in the second and third ponds of the series). Further research is needed to investigate possible limitations and to identify means to improve the performance of the UASB/PP system.

Thermodynamic parameters of micellization and transfer of amino acids from water to aqueous linear alkyl benzene sulphonate

The solution properties of linear alkyl benzene sulphonate (LABS) in water in presence of amino acids have been investigated conductometrically. The critical aggregation concentration (cac) and critical saturation concentration (csc) were determined. It has been observed that at low concentration of surfactant amino acids interact with hydrophilic head group of surfactant molecules and form molecular aggregate/micelle like structure.

Influence of Linear Alkyl Benzene Sulphonate on Corrosion of Iron in Presence of Magnetic Field: Kinetic and Thermodynamic Parameters

Implementation of linear alkyl benzene sulphonate, LAS, as corrosion inhibitor on the surface of iron metal in acidic media and in the absence and presence of magnetic field has been investigated. Adsorption of inhibitor molecules on iron surface showed Langmuir adsorption isotherms fit in acidic media. In the absence of magnetic field, apparent activation energy values (Ea) in 2.0 M HCl solutions provide evidence of the inhibitory effect of LAS on iron; similarly, the enthalpy of activation values (ΔH≠) was in accordance with activation energy values. Apparent entropy of activation shows that at larger inhibitor concentration, solvent entropy decrease in 1.0 M HCl and solvent entropy increase in 2.0 M HCl were obtained. Furthermore, spontaneity, through equilibrium constant (Kads.) values and free energy value (ΔGads.) of the adsorption process, shows a drastic decrease upon temperature increase. In the presence of magnetic field, lower rates of corrosion, larger activation energies, solvent entropy increase, larger equilibrium constant (Kads.) value, and lower free energy value (ΔGads.) have been investigated.

Decreases in Surface Activities and Aquatic Toxicities of Linear Alkylbenzene Sulfonate and Alcohol Ethoxylates during Biodegradation

We discussed the relation between aquatic toxicity and interfacial activity during biodegradation with using LAS (Linear Alkylbenzene Sulphonate) and AE (Alcohol Ethoxylate). The change of death rate of Daphnia magna, surface tension, concentration of surfactant, and biodegradation by oxygen demand during biodegradation were measured. As a result, a rapid decrease in toxicity and rapid increase in surface tension were observed within the time before biodegradation based on oxygen demand started to increase. These rapid changes in toxicity and surface tension occurred due to the structural change of surfactant molecules in the primary biodegradation process, which was confirmed by HPLC (High Performance Liquid Chromatography) analysis. We also performed re-addition test to study the effects of acclimatization since it takes an important role on boidegradation, and found that the acclimatization significantly accelerated the primary biodegradation, which were indicated by increase in surface tension and decrease in aquatic toxicity. These results show that the environmental risk of surfactants should be considered not only with the biodegradation based on oxygen demand but also with the decrease of interfacial activity through the primary biodegradation process.

Molecular geochemical indicators of sewage input in the Antarctic coastal area (Admiralty Bay, King George Island, Antarctica)

Antarctica has been described as a pristine environment for many years. However, human presence has resulted in fossil fuel combustion, vehicular emissions, fuel spills in the marine and terrestrial environments and sewage waste discharged into the ocean. Currently, most Antarctic research stations (around 79 scientific centres) are located in coastal areas, and they release their untreated sewage containing domestic waste directly into the marine environment. A group of molecular tracers such as steroids and linear alkylbenzenes (LABs) have been successfully used to investigate domestic waste discharges and faecal contamination in different regions, including Admiralty Bay, Antarctica (Martins et al., 2002; 2005). Coprostanol (5β-cholestan3β-ol) and coprostanone (5β-cholestan-3-one) have been widely used as faecal contamination markers because they are present in human faeces (Figure 1). Additionally, epicoprostanol (5β-cholestan-3β-ol) indicates the level of treatment of the faecal matter as it is formed during the extensive anaerobic sewage treatment of wastewaters (Figure 1). Also, LABs are present at levels from 1 to 3% in surfactants and detergents with linear alkylbenzene sulphonates (LASs) due to incomplete sulfonation (Figure 2), and they are frequently discharged via sewage outfalls together with faecal matter. These compounds are usually preserved in the sediment, and can be used as molecular tracers of domestic wastes. The monitoring of environmental conditions, such as hydrocarbon levels (Martins et al., 2004; 2010) and PCBs, near the sewage discharge from the Comandante Ferraz Brazilian Research Station, located at Martel Inlet, Admiralty Bay, King George Island, has been carried out since the austral summer of 1996/97. The aim of this study is to evaluate the sewage contribution from Ferraz station to Admiralty Bay and to compare the historical trend reported in previous studies. This evaluation is based on the results of molecular geochemical indicators such as steroids and LABs from the upper layer of sediments sampled during the austral summers of 2009/10. In Antarctica, monitoring the extent of sewage pollution dispersal is essential as Antarctic Treaty signatory nations must conform to the Protocol on Environmental Protection. Admiralty Bay is the largest around King George Island. The bay area is an Antarctic Specially Managed Area (ASMA), and the Scientific Committee on Antarctic Research (SCAR) has recommended environmental studies on present-day conditions of the region. Most sampling sites were located near Ferraz station. This medium size station was established in the summer of 1984, and usually has a population of approximately 50 people during the summer. The sewage system receives intermediate primary and secondary treatment before being discharged through a short pipe (Figure 3) near the sea. The sewage treatment system has been in operation since the austral summer of 1995/96 and was designed to serve a population of 50. For analyses of steroids, sediments are extracted using a Soxhlet system for 8 hours with 70 mL of ethanol. The concentrated extract is submitted to a clean up with column chromatography with deactivated alumina and elution with 15 mL of ethanol. The extract is evaporated till completely dry and derivatized to form trimethylsilyl ethers 4

Morpho-histochemical changes in the liver and intestine of young giltheads (fish-nursery), Sparus aurata, L., induced by acute action of the anionic tensioactive alkylbenzene sulphonate.

In the present study we have assessed the effect on the survival and the morpho-histochemical changes in the liver and intestine of young giltheads (fish-nursery), Sparus aurata, L., induced by acute action of the anionic tensioactive, alkyl benzene sulphonate (ABS). Firstly, the LC50 of ABS at 96 hours was found to be 0.6 mg/L. Secondly, lots with 50 young giltheads (fish-nursery) were exposed to ABS concentrations of 0.5, 1, 3 and 5 mg/L, to obtain the surface tension value and exposure time required for 50% mortality of the specimens at each tested concentration. Exposure to ABS caused several forms of histopathological damage in the liver (the radial arrangement of hepatocytes was lost) and intestine (destruction of the structure of villi and increase in thickness of the other three layers). In addition, changes in bio-macromolecule components (proteins in general, siderophile proteins, neutral mucopolysaccharides, glycogen and acid mucopolysaccharides) were observed. The degree of these alterations was dependent upon the ABS concentration. These changes could have detrimental effects on the growth and survival of the species.

The use of marine benthic diatoms in a growth inhibition test with spiked whole-sediment

The benthic diatom Cylindrotheca closterium was exposed to whole-sediment spiked with the synthetic surfactant Linear Alkylbenzene Sulphonate (LAS), as commercial mixture or individual homologues (C10-LAS, C11-LAS or C12-LAS). Separately, the diatoms were exposed to C12-LAS in a water-only system. The algal growth was determined after 72 h. The 72-h ErC50 values ranged from ≤4 to 29 mg/kg sediment, suggesting that C. closterium was sensitive to LAS. The outcomes were reproducible with a variation factor lower than 3, showing the reproducibility of the method. The test set up was cost effective, used little bench space and employed a micro-phytobenthos species that fulfilled most of the criteria for a suitable test species in sediment systems. The 72-h ErC50 obtained in a water-only system (0.141 mg/L) was ca. 2 orders of magnitude lower (0.002 mg/L). This was likely due to an indirect effect of the use of fresh sediment.

Lethal toxicity of industrial detergent on bottom dwelling sentinels

Abstract We used fresh and brackish water shrimp ( Desmoscaris trispinosa and Palaemonetes africanus), in sediment bioassays to assess the toxicity of an industrial detergent containing high levels of anionic surfactant (linear alkylbenzene sulphonate (LAS)). The Organization for Economic Cooperation and Development (OECD), # 218 direct sediment toxicity assessment was employed. The organisms were exposed to different concentrations (31.25, 62.5, 125, 250 and 500 mg/kg) of the chemical (Neatex) in replicate treatments. Percentage mortality was measured as the ecological endpoint. Mean mortality and estimated lethal concentration LC 50 values varied with species type, concentration and exposure duration. The statistical variation in the observed mean mortality of the test organisms in the chemical and the control treatment shows that mortality may be induced by the effect of the chemicals. The lethal concentration ( LC 50 s) was significantly different at levels of p < 0.05 for the fresh and brackish water experiments. Consequently, assessment of water and sediment quality as a result of chemical pollutants was necessary for protecting some of the more sensitive benthic invertebrates representing the major proportion of the diet of many species in the Niger Delta ecological zone.

Automated Determination of Linear Alkylbenzene Sulphonate (LAS) in Wastewater Treatment Plants Effluents Using on Line Solid-phase Extraction Followed by HPLC with Fluorescence Detection

Abstract An on line SPE (solid-phase extraction) method followed by HPLC with fluorescence detection has been developed and validated for determining the LAS in inlet and outlet effluents of wastewaters treatment plants. Filtered effluent samples were on line concentrated on a small polymeric reversed phase column, then the trapped LAS are separated on a specialty polar-embedded reversed-phase column and detected by a fluorimeter. The on line SPE method with fluorescence detection showed very good repeatability (from 1.5 to 11.7% depending on the sample loading volume) and robustness with detection limits of 1.5 μg l−1 for total C10–13 LAS loading a 5 ml sample volume. This automated method is a cost-effective way to determine LAS also in routine monitoring of inlets and outlets of wastewater treatment plants allowing to optimize treatment procedures.

Organic contaminants in sewage sludge (biosolids) and their significance for agricultural recycling

Organic chemicals discharged in urban wastewater from industrial and domestic sources, or those entering through atmospheric deposition onto paved areas via surface run-off, are predominantly lipophilic in nature and therefore become concentrated in sewage sludge, with potential implications for the agricultural use of sludge as a soil improver. Biodegradation occurs to varying degrees during wastewater and sludge treatment processes. However, residues will probably still be present in the resulting sludge and can vary from trace values of several micrograms per kilogram up to approximately 1 per cent in the dry solids for certain bulk chemicals, such as linear alkylbenzene sulphonate, which is widely used as a surfactant in detergent formulations. However, the review of the scientific literature on the potential environmental and health impacts of organic contaminants (OCs) in sludge indicates that the presence of a compound in sludge, or of seemingly large amounts of certain compounds used in bulk volumes domestically and by industry, does not necessarily constitute a hazard when the material is recycled to farmland. Furthermore, the chemical quality of sludge is continually improving and concentrations of potentially harmful and persistent organic compounds have declined to background values. Thus, recycling sewage sludge on farmland is not constrained by concentrations of OCs found in contemporary sewage sludges. A number of issues, while unlikely to be significant for agricultural utilization, require further investigation and include: (i) the impacts of chlorinated paraffins on the food chain and human health, (ii) the risk assessment of the plasticizer di(2-ethylhexyl)phthalate, a bulk chemical present in large amounts in sludge, (iii) the microbiological risk assessment of antibiotic-resistant micro-organisms in sewage sludge and sludge-amended agricultural soil, and (iv) the potential significance of personal-care products (e.g. triclosan), pharmaceuticals and endocrine-disrupting compounds in sludge on soil quality and human health.