The Effects of Natural Conditions
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1. Literature Review
1.1. Disintegration of Linear Alkylbenzene Sulfonate
Linear alkylbenzene sulfonate is used in numerous domestic cleaning supplies and laundry abstergents as one of the principal cleaning components. Its concentration in domestic consumer cleaning products does not exceed 25%, while in commercial and industrial cleaning products its concentration is higher. One molecule of linear alkylbenzene sulfonate includes an aromatic ring that is connected with a linear alkyl chain at any possible position, sulfonated at the para position with the exception of terminal carbons (Valtorta et al., 2000). In turn, the chain of linear alkyl carbon usually contains from ten to fourteen atoms of carbon. Its estimated mole ratio is typically in the range between 11.7 and 11.8.
In 1964, linear alkylbenzene sulphonate was introduced as an anionic surfactant in order to readily replace highly branched alkylbenzene sulphonate with a biodegradable one. In general, linear alkylbenzene sulfonate is a combination of strongly related homologues and isomers (HERA, 2009; Cavalli, et al., 1999; Schonkaes, 1998).
1.1.1. Production and use of linear alkylbenzene sulfonate
Linear alkylbenzene sulfonate is produced from linear alkylbenzene in enclosed and self-contained systems (OECD SIDS, 2005). In turn, linear alkylbenzene is manufactured from the reaction of benzene and paraffins. At the initial stage of LAS production, intermediate linear alkylbenzene sulfonic acid is manufactured. This intermediate acid is mainly produced in batch or enclosed sulfonation facilities’ continuous processing equipment with the help of air/SO3 and oleum sulfonation. Jointly with a catalyst, linear alkylbenzene is further isolated with the help of distillation. Linear alkylbenzene is subsequently sulfonated. Finally, it is neutralized to sodium salts of linear alkylbenzene sulfonate (OECD SIDS, 2005).
Starting from the mid-1960s and until now, sulphonation technology has been considerably improved. Even though oleum is still frequently used in the production of linear alkylbenzene sulfonate, modern approaches are applied. The majority of sulphonation facilities in European countries extensively use SO3 gas and falling film reactors (either mono-tube or multi-tube). Moreover, these modernized plants typically employ both the sulphation of fatty alcohols, as well as the sulphonation of linear alkylbenzene (HERA, 2009).
Linear alkylbenzene, the forerunner of linear alkylbenzene sulfonate, is produced in the course of industrial processes of large scales through alkylating benzene with the help of alkyl halides (for example, chloro-paraffins) or linear mono-olefins by using AlCl3 and HF in the form of the alkylation catalyst (Cavalli et al., 1999). The quality of linear alkylbenzene manufacturing is measured with its color indexes, bromine, alkyl chain linearity, and impurities (Marr et al., 2000). Using AlCl3 in the process of alkylation was the first industrial process of LAS production that was largely used in the mid-1960s when linear alkylbenzene replaces branched dodecylbenzene. Later, at the end of the 1960s, the HF technology started being intensively used as a favored technology of linear alkylbenzene production (HERA, 2009).
Detal® is a new alkylation technology that was developed in the middle of the 1990s. It is based on the application of assorted catalyst in a fixed-bed reactor (Berna et al., 1994). Soon after the launch on the market, this technology was rapidly adopted by numerous producers. Substantial advantages were offered by this new technology, unlike previous production techniques. The major advantages of alkylation technology include simplification of the production process, improvement of the overall production yield, enhanced quality of linear alkylbenzene, and abolition of disposal and handling acids, such as HF and HCl (HERA, 2009).
In 2005, the total global production of linear alkyl benzene constituted more than 3 million tons. According to the distribution of manufactured linear alkylbenzene by the technology that was used for its production in the same year, 75% of LAB was manufactured using HF, 5% with the help of AlCl3, and 20% of LAB was fixed-bed. In Europe, the estimated capacity of LAB production in 2005 was approximately 600 kt/y. This twice exceeded the existing demand (CESIO, 2005; ECOSOL, 2005).
Linear alkylbenzene sulfonate that is used for commercial purposes is entirely produced in the form of blend of alkyl chain homologues C10, C11, C12, C13, and sometimes C14. The average length of the alkyl chain varies from C11.3 to C12.6, including the length of the leading materials’ alkyl chain varying from C11.7 to C11.8. Every homologue of the alkyl chain comprises a blend of all feasible sulfophenyl isomers with the exception of the 1-phenyl isomer that is not common in materials used for commercial purposes. The catalyst that is used to manufacture linear alkylbenzene fully establishes phenyl isomers’ distribution in commercial linear alkylbenzene sulfonate with the percentage of the 2-phenyl isomers varying between 18% and 28% (Valtorta et al., 2000). As a result, linear alkylbenzene that is used for commercial purposes is composed of a blend of more than 20 components, including C10 homologue of the 2-phenyl to 5-phenyl isomers, C11 and C12 homologues of the 2-phenyl to 6-phenyl isomers, and, finally, C13 homologues of the 2-phenyl to 7-phenyl isomers (Valtorta et al., 2000).
More than 95% of materials that are used for commercial purposes include pure linear alkylbenzene sulfonate. There is evidence that a little share of methyl-substituted (for example, iso-branched) linear alkylbenzene sulfonate can be present in the blend (Nielsen et al., 1997). However, it should be noted that this share of iso-linear alkylbenzene sulfonate is substantially small (from 1% to 6% only). Moreover, it has been proved that this substance does not prohibit biodegradation compared to the pure linear component of alkylbenzene sulfonate (Cavalli et al., 1996; Nielsen et al., 1997).
Finally, depending on the production process, other non-linear compounds can be present with their share not exceeding 8%, for instance, dialkyltetralin sulfonates. Likewise, dialkyltetralin sulfonates similar to iso-linear alkylbenzene sulfonates are found to be biodegradable (Nielsen et al., 1997). Recent enhancements in processing techniques in Europe, Japan, and the United States have resulted in the increase of linear alkylbenzene sulfonate’s yields in addition to the reduction of the dialkyltetralin sulfonates’ share. Thus, it has been historically established that the share of pure LAS varied from 87% to 98%. Currently, according to latest evidence, less than 5% of manufactured LAS all over the world contains relatively high shares of dialkyltetralin sulfonates (OECD SIDS, 2005).
1.1.2. Linear alkylbenzene sulfonate in the USA
Data about volumes of production and consumption of linear alkylbenzene sulfonate, potential environmental exposures, and release primarily come from official sources of the Industry Coalition member companies, which provided information to the SIDS Assessment of linear alkylbenzene sulfonate that jointly comprise approximately 75% of the production of LAS in North America. Overall, in 2000, about 390,000 metric tons of linear alkylbenzene sulfonate were consumed in North America, including Canada and the United States combined (Colin A. Houston, 2002). Similarly, the manufacturing of linear alkylbenzene sulfonate in Europe in the same year constituted around 400,000 metric tons. Moreover, Japanese production of linear alkylbenzene sulfonate in 2001 comprised approximately 85,000 metric tons. In general, the world production of linear alkylbenzene sulfonate was 2.6 million metric tons in 1995 (EU Risk Assessment Report for LAB, 1997).
According to evidence from the survey conducted by SIDS Coalition in 2002, a vast majority of linear alkylbenzene sulfonate (from 78% to 97% of all LAS) is consumed in the form of powder and liquid, as well as commercial fine fabric and laundry detergents. Moreover, remaining 2%-10% of the manufactured linear alkylbenzene sulfonate is consumed in the form of commercial and consumer dishwashing liquids. Therefore, based on the use of linear alkylbenzene sulfonate, the leading disposal route for products with LAS is through wastewater. Table 2 provides information about the share of linear alkylbenzene sulfonate in different types of commercial and consumer detergent products in North America (OECD SIDS, 2005).
According to the findings of broad monitoring evaluations of the environmental situation in the United States, estimated concentrations in surface water were typically below 50 µg/L in river water samples, which had been collected in low intensity conditions below the mixing zones of the treatment plant. Moreover, values across the 2,800 km distance of the Mississippi River, starting from Minneapolis and ending near New Orleans, vary from non-detectable (share below 0.1 µg/L) to 28 µg/L. Similar findings of the linear alkylbenzene sulfonate concentration in river water were obtained in analogous studies that had been carried out in Japan and Europe (OECD SIDS, 2005).
The evaluated concentration of linear alkylbenzene sulfonate in the river sediments was typically less than 1-2 mg/kg of dry weight. Moreover, sediments in the Mississippi River were found to be less than 1 mg/kg of the dry matter. In comparison, the concentration of LAS in sediments of the Tiber River in Italy was reported at a twice higher rate – 1.8 mg/kg of the dry matter. At the same time, substantially higher concentrations of linear alkylbenzene sulfonate were found near poorly treated or completely untreated wastewater discharges. For example, the concentration of LAS in sediments of Rapid Creek river in the United States were reported to be 5.3 mg/kg on the distance of more than 5 miles downstream along the river, 11.2 mg/kg in the area from the outfall and 5 miles downstream from it, and 190 mg/kg just below the outfall (OECD SIDS, 2005).
1.1.3. Degradation of linear alkylbenzene sulfonate
Primary degradation of linear alkylbenzene sulfonate is a transformation process that is stimulated by microorganisms with further development of biodegradation intermediaries in the form of sulphophenyl carboxylates (Swisher, 1987). This stage of the degradation transformation process corresponds to the loss of toxicity to living organisms that are present in the environment, loss of interfacial activity, and disappearance of the parent molecule (Kimerle, 1989; Kimerle et al., 1977). Further transformations in the course of the degradation process include the aromatic ring cleavage followed by the complete conversion of linear alkylbenzene sulfonate and sulphophenyl carboxylates into the form of inorganic substances (Na2SO4, CO2, H2O). During the final stage of the degradation process, its constituents are incorporated into the biomass composed of micro-organisms (Karsa & Porter, 1995).
Using certain pure unlabeled homologues and a 14C ring-labeled commercial product in a STP simulating laboratory equipment was one of the first attempts to show proof that the alkyl share as well as the ring portion of linear alkylbenzene sulfonate can comprehensively degrade in the environment and ultimately change to CO2 (Nielsen & Huddleston, 1981). The application of different tests shows that more than 99% of linear alkylbenzene sulfonate is primarily degradable. The degree of its degradation is measured with either methylene blue active substance or with the help of detailed analytical tools, including high performance liquid chromatography (OECD, 1993; EU Commission, 1997). Moreover, complete degradation of linear alkylbenzene sulfonate is found to be in a range from 80% to more than 95% when it is measured with dissolved organic carbon and continuous activated sludge tests respectively. At the same time, the degree of ultimate degradation of LAS is found to be around 95-98% when it is measured with the help of inherent tests (EU Commission, 1997).
The degradation of commercial linear alkylbenzene sulfonate products has been tested with the help of CAS simulation tests in the temperature range from 9°C to 25°C (Prats et al., 2003). Under different temperatures, the time of the acclimation phase was considerably different. It was found that it takes more time to degrade under lower temperatures, and, vice versa, the degradation of commercial LAS is faster under higher temperatures. However, the share of linear alkylbenzene sulfonate removal that was measured with the help of HPLC and MBAS were found to be comparable and high (more than 95%) in all cases. These findings imply that the community of microorganism can also attain a proper acclimation, as well as the fact that kinetics is also found to be sufficient under the conditions of low temperatures (Leon et al., 2006; Prats et al., 2006). The findings are consistent with conclusions of stream mesocosm studies which suggest that under reasonable environmental conditions, surfactants mineralization at least can be maintained when different algal species are acclimated along with the fluctuation of natural temperatures. At the same time, mineralization can often be increased during the time of a considerable decline in seasonal temperature (Lee et al., 1997).
According to the EU Commission (1997), commercial linear alkylbenzene sulfonate products are readily degradable. It is believed that a ten-day window is not crucial for the assessment of the readiness for the complete degradation of detergents’ surfactants (CSTEE, 1999). Yet, there is evidence in the literature that linear alkylbenzene sulfonate passes the rule of the ten days window. This was confirmed with numerous tests, including OECD 301 F tests (Temmink et al., 2004), the evolution study of comparative CO2 (Ruffo et al., 1999), OECD 301B evolution test of CO2 (LAUSa, 2005), mineralization test under ISO 14593/1999 according to the Detergent Regulation 648/2004 (Lòpez et al., 2005), and the DOC die-away test (LAUSb, 2005). In addition, it is reported that during persistent degradation, intermediates are not created as it is shown with high tier tests (Cavalli et al., 1996; Gerike et al., 1986; Moreno et al., 1991). Intermediates of the degradation process, for example, sulphophenyl carboxylates, are found to be not persistent as well as their toxicities are considered to be lower by several orders of magnitude, compared to that of the parent molecule (Kimerle et al., 1977).
For risk assessment purposes of the LAS degradation, the degree of the primary degradation instead of the ultimate degradation is considered to be a relevant parameter for the estimation. This choice is explained by a relatively lower toxicity of transient degradation products and the absence of persistent metabolites. A number of unique analytical tools have been developed for the biodegradation risk assessment of linear alkylbenzene sulfonate, including Gas Chromatography/Mass Spectrometry approach, a High Performance Liquid Chromatography method, and Liquid Chromatography/Mass Spectrometry. All of them are able to make relevant kinetic data available for exposure assessments (Di Corcia et al., 1999; Matthijs et al., 1987; Trehy et al., 1996).
Significant kinetics degradation characteristics of linear alkylbenzene sulfonate have been found with the help of a die-away laboratory test. It has applied original testing procedures with respect to radio-labeled materials, which measured the evolution of 14CO2 with Liquid Scintillation Counting followed by the degradation with the help of Radio Thin-layer Chromatography (Federle et al., 1997). Using these innovative approaches, it was shown that the primary degradation rate of linear alkylbenzene sulfonate is approximately 10-15 times lower compared to the one estimated with the help of the activated sludge in the form of a test medium (Federle et al., 1997).
At the same time, there is evidence that kinetics of linear alkylbenzene sulfonate is faster in field studies that are carried out under sensible environmental conditions close to real, compared to the findings of laboratory studies (Fox et al., 2000; Schroder, 1995; Takada et al., 1994). This is explained by the presence of more favorable conditions for degradation in the real environment unlike the ones that are reproduced in the laboratory.
1.1.4. Environmental exposure of linear alkylbenzene sulfonate
Relevant information for the primary mechanisms of linear alkylbenzene sulfonate degradation is generally obtained from the environmental fate data. At the same time, environmental fate data serve as an indicator of the pattern of differences that are observed between chemicals. Considering organic chemicals, environmental fate data normally include information about the breakdown of their compounds into smaller constituents in the course of biological degradation. Other mechanisms of chemicals’ breakdown include hydrolysis and photolysis. These two breakdown mechanisms are largely reliant on air, soil, water, and different sediments as environmental compartments to which chemicals are primarily distributed. In order to evaluate the relative share of chemicals that can be divided into different constituents at a steady state, fugacity modeling can be applied. Estimation results of the environmental distribution of linear alkylbenzene sulfonic acids are presented in Table 3 (USEPA, 2000).
The estimation of predictability of change in the toxicity of aquatic organisms with structural differences in materials is considered to be a primary pattern from ecotoxicity. Moreover, there is a need to estimate whether chemical and physical characteristics of chemicals, such as linear alkylbenzene sulfonate, have impact on their bioavailability and, as a result, their aquatic toxicity (Compliance Services International, 2004).
The assessment of chemicals’ toxicity to mammals serves as a key substitute indicator for evaluating potential impact on people. Similarly, there is a need to estimate patterns in the data that determine its endpoints without values. This provides a possibility to derive evaluations of the patterns from the available data and draw conclusions for the entire population. There are some aspects of mammalian toxicity that should be estimated. With the help of acute testing, information about gross effects can be obtained, including mortality rates from the exposure to high doses. In addition, information about toxicity that is related to multiple doses is assessed with the help of the repeated dose testing.
On the other hand, genetic testing is carried out in order to estimate the potential of mutagenic effects by using in vivo systems (such as live animals), nonbacterial systems (for example, cell transformation), and bacterial systems (for example, the Ames test). Furthermore, developmental, teratogenic and reproductive tests are used to collect information about impending effects of long-term exposure to relatively smaller doses on mammals, mainly including effects that are associated with young animals and developing embryos. Finally, lack of considerable exposure has the potential to avert the need to fill up noticeable gaps in data on tests on mammals (Compliance Services International, 2004).
In the course of the evaluation of acute toxicity, there are three principal directions of the exposure. First, there is oral exposure when the tested substance that is either brought into food or directly given to the animal with the help of gavage. Second exposure is through inhalation, when the substance in question is brought into the lungs. Finally, dermal exposure is the third approach to testing exposure when the substance is directly applied to the skin. The selection of the exposure testing approach primarily depends on chemical and physical properties of the tested substance, as well as a possible direction by which both people and animals would be exposed. However, the data that are needed for all the three directions of exposure are often not sufficient to recognize a particular acute toxicity of chemical substances (Compliance Services International, 2004).
There is evidence in the literature about acute oral toxicity of linear alkylbenzene sulfonate (Compliance Services International, 2004). The findings of research studies indicate that toxicity of LAS is reported to be in the range from minimal to moderate, having values of LD50 in the array from 500 to 2000 mg/kg of body weight. At the same time, there are data on acute inhalation of linear alkylbenzene sulfonate. It suggests that there is lack of LAS’ considerable toxicity. Moreover, data on the dermal exposure of linear alkylbenzene sulfonic acids also proves that there is a lack of its significant toxicity. Also, vitro bacterial genetic toxicity studies of linear alkylbenzene sulfonate as well as in vitro non-bacterial studies have reported negative results for mutagenicity of LAS. Finally, lack of significant effects of linear alkylbenzene sulfonate is found with respect to repeated dose exposures, developmental toxicity and teratogenicity, and reproductive toxicity. Therefore, consistency in the research findings indicates that linear alkylbenzene sulfonate has low risks for the environment, as well as toxicity for people and animals (Compliance Services International, 2004).
In general, the toxicity of linear alkylbenzene sulfonic acids for mammals has been extensively studied and characterized in the literature, principally when data on linear alkylbenzene sulfonate have been taken into consideration. The findings of research studies suggest a lack of significant toxicity for mammals. At the same time, there are available data on the effects of linear alkylbenzene sulfonate with respect to developmental and reproductive endpoints and repeated dose exposures. Impending occupational exposures are mostly alleviated with the help of the application of personal protective equipment and closed production systems. Hence, there is no obvious need for additional testing of LAS’ toxicity in order to derive properties of its environmental exposure and toxicity (Compliance Services International, 2004).
1.2. Biological Indicators of Linear Alkylbenzene Sulfonate Disintegration
1.2.1. Disintegration of LAS in anaerobic conditions
Modern laboratory simulation and screening tests (ERASM, 2007; ECETOC, 1994) provide assessment of the final biodegradation of linear alkyl benzene sulfonate with the help of the identification of the ultimate gas production (CH4 and CO2) in the course of approximately two months of the incubation period. The findings of these tests indicate that linear alkylbenzene sulfonate shows no noteworthy biodegradation (ERASM, 2007; Federle & Schwab, 1992; Garcia et al., 2005; Gejlsbjerg et al., 2004; Steber & Wierich, 1989; Steber, 1991). Only after several months of the incubation period, the loss of parent linear alkylbenzene sulfonate was claimed (Prats et al., 2000). Nevertheless, given oxygen-limited conditions of tests that are close to environmental conditions in the real world, biodegradation of linear alkylbenzene sulfonate can be started and further continued in anaerobic conditions (Leon et al., 2001; Larson et al., 1993).
There is evidence in the literature that certain inocula are able to transform linear alkylbenzene sulfonate under specific anaerobic conditions, for example, in the environment with a limited amount of sulphate where LAS would be the single source of sulfur (Denger et al., 1999). At the same time, findings of several studies indicate that linear alkylbenzene sulfonate has the capacity to biodegrade under methanogenic conditions. However, the given waste water’s low bioavailability of treatment plant reactors in reality is found to be a major obstacle to considerable biodegradation of LAS (Mogensen et al., 2003; Angelidaki et al., 2000).
According to Angelidaki et al. (2000), Haggensen et al. (2002), and Sanz et al. (1999), biodegradation of linear alkylbenzene sulfonate reaches 5-44% degree in upflow anaerobic sludge blanket reactors and 14-25% degree in continuous stirred tank reactors. Overall, evidence suggests negligible direct ecological relevance of LAS biodegradation under strict anaerobic conditions (ERASM, 2007; Heinze et al., 1994). According to the Scientific Committee on Health and Environment Risks, which represents an advisory committee of experts within the European Commission on threats that are posed by detergent surfactants to the environment, including linear alkylbenzene sulfonate, “A poor biodegradability is not expected to produce substantial modifications in the risk for freshwater ecosystems under anaerobic conditions since the surfactant removal in the STPs is deemed to be regulated by its aerobic biodegradability.” Therefore, the adoption of the requirement for complete biodegradability of linear alkylbenzene sulfonate in anaerobic conditions cannot be considered as a useful measure for environmental protection (SCHER, 2005).
Conversely, the importance of anaerobic biodegradation has been proven in ecological risk assessment according to the following rationale (HERA, 2009). Considering anaerobic conditions for biodegradation, particular attention should be paid to the low redox potential, implying that NO3-, SO42- or CO2 replace O2 as eventual electron acceptors. Given these reduced environmental conditions, the assessment of the effects should also incorporate certain organisms, for example, protozoa, which are anaerobic bacteria. Therefore, such aquatic organisms as crustaceans, fish, and algae that are usually taken into consideration for the assessment of effects are not representative of these anaerobic communities. Even though the deep anoxic sediments remain to be a live environment for macro-invertebrates, they are typically found in oxic micro-environments, for example, in burrow. Hence, the evaluation of the surfactants’ threats to these organisms living in the burrowed environment would require a modelling of deep sediment diffusion of surfactants as well as the degree of the biodegradation after the restoration of oxic conditions (HERA, 2009).
In the framework of risk assessment studies of anaerobic environments, anaerobic bacteria are used as a biological indicator. The findings suggest that the concentration of linear alkylbenzene sulfonate up to 30 g/kgdw sludge is not able to have a negative impact on microbial processes in these digesters (Berna et al., 1994). The effect of linear alkylbenzene sulfonate on the digestion process of anaerobic sludge indicates that toxicity on anaerobic microorganisms is largely determined by the concentration of bioavailable homologues of LAS in the STP anaerobic digesters’ liquid phase (Garcia et al., 2005). Hence, poor original degradation of linear alkylbenzene sulfonate in anaerobic discontinuous systems has been proved, implying that the biogas production inhibition extent is notably associated with the sludge used as an inoculum (Garcia et al., 2005).
1.2.2. Disintegration of LAS in soil
Several measurement studies of linear alkylbenzene sulfonate in sludge-amended soil have been conducted both in the field and in the laboratory (Cavalli et al., 1999). These research studies have been carried out on soil after the appliance of sludge that contained linear alkylbenzene sulfonate at levels that are considerably higher than those that are recommended in agriculture (TGD, 2003). For instance, the annual average rate of sludge spreading was reported at the level of 6 t/ha in the United Kingdom and Germany (Holt et al., 1989; Matthijs & DeHenau, 1987), 13.5 t/ha in Switzerland (Marcomini et al., 1988), and 32 t/ha in Spain (Prats et al., 2003). Researchers have concluded that the estimated removal rate of linear alkylbenzene sulfonate corresponded to half-lives in the array from 3 to 33 days.
In the framework of the laboratory studies, the most trustworthy findings were obtained by analyzing mixtures of sludge and linear alkylbenzene sulfonate spiked soils with the help of 14C materials, which estimated complete biodegradation. Mineralization half time of linear alkylbenzene sulfonate was found to be in the range from 7-8.5 days (Gejlsbjerg et al., 2004) to13-26 days (Figge & Schoberl, 1989). Taking a lag of time in 1.9-2.5 days and concentration of LAS in soil at the level of 10 mg/kgdw, the mineralization rate of LAS was found to be equal to 2.1-2.6 days. However, this concentration of LAS is considered to be one of the highest possible environmental concentrations of the surfactant in soil that is used in agriculture (Gejlsbjerg et al., 2004).
14C-labelled linear alkylbenzene sulfonate in laboratory sludge-soil mixtures with the concentration rate in the µg/kgdw soil range that corresponds to the expected steady concentrations of the surfactant in sludge-amended soil at least after a 30-day waiting period from the sludge application has been also studied (Gejlsbjerg et al., 2004). Following a relatively long time, at least 2 weeks, the mineralization of linear alkylbenzene sulfonate has been taking place at a rapid pace, comprehensively depicting kinetics in two phases. The first phase of speedy mineralization occurs in 2 days. Then it is followed by the 7.9 day phase of slow mineralization of LAS in soil. This slow phase of mineralization is most likely governed by desorption and sorption processes that take place in soil. Moreover, subsurface soils, which have been evaluated in laboratory biodegradation and sorption studies and sampled below a septic system drain field using radiolabeled materials and groundwater, are also found to have the capacity to mineralize linear alkylbenzene sulfonate from 0.5 to 8.7 days (Doi et al., 2002).
Nevertheless, the majority of field monitoring and laboratory studies of sludge-amended soil are focused on the evaluation of the LAS’ disappearance in soil. This implies that only primary degradation is considered.
According to Elsgaard et al. (2001), the primary biodegradation of LAS exceeded 73% in the course of only two weeks. On the other hand, in the soil mesocosm study, the primary degradation of LAS in soil is reported to be 1-4 days (Elsgaard et al., 2003). Finally, a field study that has been carried out in conditions close to the ones which are recommended in agriculture has shown that primary degradation of LAS lasts for 3-7 days (Kuchler et al., 1997).
1.3. Natural Effects on LAS Disintegration in Water
1.3.1. Effects of light on LAS disintegration in water
Chemical properties of the microenvironment in river or sea water are significantly affected by the photosynthesis of algae. Yet, there is limited evidence of the effects of photosynthesis and diurnal variation on the behavior of organic pollutants, such as linear alkylbenzene sulfonate. Linear alkylbenzene sulfonate is considered to be a bright example of non-persistent organic pollutants that is used in the analysis of the degradation of this type of pollutants under the impact of natural biofilms and light.
Using laboratory batch experiments, Hua et al. (2012) paid special attention to the assessment of the role of light in the course of LAS degradation. Applying both fully active biofilms and illumination, the maximum decrease of linear alkylbenzene sulfonate was found, with approximately 75% of linear alkylbenzene sulfonate being removed after the degradation experiment with a 36-h duration. In addition, it was found that the removal of linear alkylbenzene sulfonate is dominated by photosynthesis of the biofilms. At the same time, lesser roles were attributed to adsorption and degradation by the biofilms, while the role of direct photolysis was reported to be insignificant. Finally, studies confirm that the photosynthesis of algae plays a considerable role in the course of LAS degradation (Hua et al., 2012).
1.3.2. Effects of temperature on LAS disintegration in water
Degradation of linear alkylbenzene sulfonate in water is largely affected by temperature. The impact of temperature on the process of LAS degradation is often estimated in research studies with the help of a Confirmatory test that relies on the OECD 303 A method that calculates Husmann units (Prats et al., 2006). Prats, Lopez, Vallejo, Varo and Lieon (2006) investigated the effect of temperature on the degradation of LAS by carrying out experiments using a 10 mg/L initial surfactant concentration and setting up temperatures at 9, 15, and 25°C, while maintaining units of degradation inside a thermostatic compartment. The researchers found that the removal of linear alkylbenzene sulfonate exceeds 90%, despite the temperature that had been set up in the test. However, it was reported that microorganisms in water required longer periods for acclimation in lower temperatures (Prats et al., 2006).
Takamatsu, Nishimura, Inamori, Sudo and Matsumura (1996) found that with respect to the species composition in flasks and biomass, stable ecosystems are formed in water at the temperatures of 10, 20, 25, and 30°C. Moreover, it is reported that the rate of degradation of LAS in the microcosm system during the stationary phase is slower at lower temperatures, compared to the one under the condition of a high temperature. Takamatsu et al. (1996) found that aeolosoma hemprichi, philodina sp, and cyclidium glaucoma were affected by LAS more in the case of lower temperatures. At the same time, no observed effect concentration (NOEC) of linear alkylbenzene sulfonate in water was found to be less than 0.5 mg·1-1 at 10°C, 1.5 mg·1-1 and less at 20 and 25°C, and finally less than 2.5 mg·1-1 at 30°C (Takamatsu et al., 1996).
1.3.3. Effects of salinity on LAS disintegration in water
Plants which are subject to disproportionate salinity typically show signs of precise properties, such as advanced state, decreased photosynthetic activity, and precipitate senescence that is expressed in terms of visual symptoms, including necrosis and chlorosis of specific leaves. There is evidence in the literature that different species of plants exhibit exposure to salt stress that is primarily affected by carotenoids and chlorophyll loss (Lu et al., 2003; Lu & Vonshak, 2002; Neocleous & Vasilakakis, 2007) that modify the function of PSII. As a result, due to PSII’s disturbances, the decrease in photosynthetic activity is considered to be plants’ primary response to environmental stress (Baker & Rosenqvist, 2004).
In the natural environmental conditions, plants can be subjected to numerous external stresses as well as their interactions. Therefore, it is cleat that simultaneous interactions of several external stresses substantially complicate the impact on the plant, and its response is considered to be rather unpredictable owing to the antagonistic or overlapping effect. Therefore, studies of the effect of salinity on the degradation process of linear alkylbenzene sulfonate are highly important (Baker & Rosenqvist, 2004).
Terzic et al. (1992) studied properties of commercial linear alkylbenzene sulfonate during the primary stages of the degradation process. Considering cultures that originated from the saline layer and freshwater layer of water, they estimated the remaining linear alkylbenzene sulfonate during degradation experiments with the help of the reversed-phase high-performance liquid chromatography test. It provides an opportunity to assess individual homologues and isomers of LAS. The findings that were obtained with the help of the die-away approach under static conditions prove that the rate of degradation largely depends not only on the origin of the bacterial culture, structure of the alkylbenzene moiety, and temperature conditions, but also on salinity. The degradation of linear alkylbenzene sulfonate is found to be faster in the freshwater layer of the estuary, compared to the speed of LAS degradation in the saline water layer (Terzic et al., 1992).
Linear alkylbenzene sulfonate is an organic detergent that is frequently used in numerous domestic cleaning supplies and laundry abstergents in the form of one of the major cleaning components. A molecule of linear alkylbenzene sulfonate includes an aromatic ring that is connected with a linear alkyl chain at any possible position. It is sulfonated at the para position with the exception of the terminal carbons. LAS is produced from linear alkylbenzene in enclosed and self-contained systems, which is manufactured in turn from the reaction of benzene and paraffins.
Linear alkylbenzene sulfonate is found to be commonly used in the production of various cleaning supplies. In general, approximately 390,000 metric tons of LAS were consumed in the USA and Canada in 2000. From 78% to almost 97% of LAS is consumed in the form of powder and liquid, as well as commercial fine fabric and laundry detergents. As a result, the leading disposal route for products that contain linear alkylbenzene sulfonate is through wastewater. Hence, the questions of LAS effective degradation and environmental exposures have been in the focus of numerous research studies. Overall, the toxicity of LAS for people and animals has been reported to be minimal or even negligible.
However, the speed of the LAS degradation process is found to be different depending on numerous external environmental characteristics, such as light, temperature, and salinity. Overall, the degradation of LAS is reported to be faster in the environment with lower temperatures and lower rates of salinity, while light has no significant impact.
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