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EC number: 287-335-8 | CAS number: 85480-55-3
Table 1: Effect concentrations (EC10, EC50, NOEC and LOEC) for linear alkylbenzene sulfonate (LAS) toward microbial parameters in agricultural soil. All data are presented as mg/kg soil dw (Elsgaard et al., 2001a)
95% CL for EC10 value
95% CL for EC50 value
Basal soil respiration
a NA: not available
b PLFA: phospholipid fatty acid
The aim of this study was to study short-term effects of aqueous C10-C13 sodium LAS on microbial parameters in a sandy agricultural soil that was incubated for up to 11 days.
The microbial soil parameters were related to carbon and nitrogen transformation (i.e., ethylene degradation, basal respiration, and ammonium oxidation), endo- and exoenzymatic activity (i.e., dehydrogenase activity and β-glucosidase activity), anaerobic activity (i.e., iron reduction), microbial populations (i.e., cellulolytic bacteria, fungi, and actinomycetes), and a broad indicator of microbial biomass (i.e., total content of phospholipid fatty acids [PLFA]). Agricultural soil samples were incubated with test substance at nominal concentrations of 0, 8, 22, 62, 174 and 488 mg/kg dw (measured concentrations: <1, 7 ± 1, 21 ± 2, 59 ± 6, 149 ± 21 and 407 ± 52 mg/kg dw) for all the microbial soil parameters (except basal soil respiration test) for a period of 0.5-11 days. The recovery was in range of 84 to 95% of the nominal concentrations. The test concentrations for basal soil respiration (CO2 evolution) were 0, 0.8, 8, 79 and 793 mg/kg dw.
The LAS had an inhibitory effect on soil ethylene degradation, which almost ceased at the highest tested concentration. The inhibitory effect of LAS on the potential ammonium oxidation was also significant at all the tested dose levels. The inhibition of dehydrogenase activity was progressively increased at increasing LAS contents. Bacterial iron reduction was completely inhibited at 62 mg/kg. The cellulolytic microorganisms (bacteria, fungi and actinomycetes) also showed an increase in inhibition of number of colony forming units in dose dependent manner and achieve significance at 22 mg/kg dw and above test concentrations.
Soil respiration was not inhibited at any of the test concentration but, rather, caused a slight increase in CO2 production at the highest LAS contents. No effect was observed for total phospholipid fatty acids concentration. The LAS inhibited β-glucosidase activity by only 25% at the highest tested concentration of 488 mg/kg.
The resultant EC10 values for ethylene degradation, potential ammonium oxidation, potential dehydrogenase activity, iron reduction, the populations of cellulolytic microorganisms (bacteria, fungi and actinomycetes) were in the range of less than 8 to 22 mg/kg dry weight. The extracellular β- glucosidase activity was rather insensitive to C10-C13 sodium LAS with EC10 value of 47 mg/kg dw whereas the basal soil respiration was not inhibited even at 793 mg/kg dry weight. The PLFA content showed no decrease even at 488 mg/kg dw.
Table 1: Effect concentrations for aqueous linear alkylbenzene sulfonates (aq LAS) and sludge-applied LAS (LAS + sludge) toward microbial parameters in a sandy agricultural soil during incubation for 5 days to eight weeks (wk). All data are presented as mg/kg soil dw. (Elsgaard et al., 2001b)
NA: Not available
a Estimated by arithmetic interpolation, omitting an intermittent decrease in microbial biomass C.
The aim of this study was to compare the short-term effects of aqueous C10-C13 sodium LAS and LAS-spiked sewage sludge on microbial parameters in a sandy agricultural soil that was incubated for 5 days to eight weeks.
The microbial soil parameters were iron reduction, ammonium oxidation, dehydrogenase activity, arylsulfatase activity and microbial biomass C. Agricultural soil samples were incubated with LAS or LAS spiked sewage sludge at nominal concentrations of 0, 3, 8, 22, 62, 174 and 488 mg/kg dw. The measured concentrations <1, 3 ± 1, 6 ± 1, 16 ± 2, 51 ± 6, 141 ± 15 and 380 ± 25 mg/kg dw soil for aqueous LAS study and <1, NA, 6 ± 1, 16 ± 2, 44 ± 10, 118 ± 13 and 370 ± 18 mg/kg dw soil for LAS-spiked sewage sludge study. The recovery was in range of 84 to 95% of the nominal concentrations for aqueous LAS study and 71 to 76% for LAS-spiked sewage sludge study.
After 5 days of incubation, there was a complete absence of iron reduction at concentrations greater than 62 mg/kg soil dw. After 10 and 15 days of incubation, iron reduction appeared at 62 mg/kg soil dw in both soil treatments and at 174 mg/kg soil dw in the sludge-amended soil. No ammonium oxidation was observed at 174 and 488 mg/kg soil dw levels without sewage sludge, however, ammonium oxidation was detected with sewage sludge samples at same concentrations. This effect of sludge application persisted throughout the incubation period of one, two, and four weeks but was less pronounced after eight weeks of incubation. The dehydrogenase activity at all sampling occasions showed that the toxicity was higher for aqueous LAS than for LAS-spiked sewage sludge. However, there was partial or complete recovery of the LAS inhibition was seen after eight weeks of incubation. After four and eight weeks of incubation with aqueous LAS, the arylsulfatase activity was inhibited only at the level of 488 mg/kg soil dw. However, no such inhibition was seen in LAS-spiked sewage sludge samples at any of the incubation periods. The inhibitory effect of LAS after one and eight weeks of incubation was less pronounced when LAS was added with sewage sludge than as an aqueous solution. The effects of aqueous on biomass C (without sewage sludge) LAS were slightly reduced by the longer incubation time.
The EC10 values were <8 to 75 mg/kg soil dw for aqueous LAS samples and 26 to >488 mg/kg soil dw for LAS-spiked sewage sludge samples.
In conclusion, the short-term inhibitory effects of LAS on soil microbiology were decreased in the presence of sewage sludge and by a prolonged (two to eight weeks) laboratory incubation period.
Microbial parameters (10 functional or structural endpoints) were reviewed but not further used by Jensen et al. (2007) in the PNECsoil assessment as originally proposed in Jensen et al. (2001). The EC10values for microbial processes observed in the laboratory ranged from <8–793 mg aqueous LAS/kg soil dry matter (DM). Microbial iron reduction was the parameter most sensitive to LAS (extrapolated value of 5 mg/kg; Jensen et al., 2001), but this endpoint was not considered relevant for aerobic agricultural soils because the extrapolation was not well justified and in conflict with experimental data conducted under more realistic conditions (field trials) later developed by Jensen et al. (2007). Furthermore, the lowest microbial effect concentrations had been observed in the case of dosing of aqueous LAS solutions, whereas in reality LAS enters soil in a sludge matrix, where bioavailability was shown to considerably mitigate toxic effects (Elsgaard et al., 2001; Gejlsbjerg et al., 2001). For example, ammonium oxidation, an important aerobic transformation process showed a lowest EC10value of 14 mg/kg for aqueous dosing, versus 68 mg/kg for LAS in a sludge matrix (Elsgaard et al., 2001). In the latter study, microbial communities also showed a strong recovery potential (Schowanek et al., 2007).
In conclusion, terrestrial toxicity to soil micro-organisms is not needed considering the higher rate of sensitivity, and thus protection afforded by, studies on plants and invertebrates exposed to LAS under more realistic test conditions (field trials).
Jensen, J., Smith, S. R., Krogh, P. H., Versteeg, D. J., & Temara, A. (2007). European risk assessment of LAS in agricultural soil revisited: species sensitivity distribution and risk estimates. Chemosphere, 69(6), 880-892.
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