Metam-sodium

Endpoint summary

Description of key information

Biodegradation in water

Biodegradation study was conducted for 20 days for evaluating the percentage biodegradability of test substance Metam-sodium (CAS no. 132-87-6) (IUCLID dataset, 2000). The study was performed according toZahn-Wellens method under aerobic conditions. Activated sludge (not adapted) was used as a test inoculum for the study. Initial test substance conc. used in the study was 200 mg/l based on TOC removal, respectively.The initial TOC concentration after 3 hours was -21%.The percentage degradation of test substance Metam-sodium was determined to be 1, 8, 84 and 77% by DOC removal or COD parameter parameter in 20 days. Thus, based on percentage degradation, Metam-sodiumis considered to be readily biodegradable in water.

Biodegradation in water and sediment

Estimation Programs Interface (EPI Suite, 2018) prediction model was run to predict the half-life in water and sediment for the test compound Metam-sodium (CAS No. 137 -42 -8). If released in to the environment, 21.2% of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of Metam-sodium in water is estimated to be 15 days (360 hrs). The half-life (15 days estimated by EPI suite) indicates that the chemical is not persistent in water and the exposure risk to aquatic animals is moderate to low whereas the half-life period of Metam-sodium in sediment is estimated to be 135 days (3240 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.0899%), indicates that Metam-sodium is not persistent in sediment.

Biodegradation in soil

Biodegradation study in soil was conducted for determining the half-life of the chemical Metam-sodium (CAS no. 137-42-8) (J.H. Smelt, et. al; 1989). Soils for the transformation studies were collected from: a) field trials, b) "problem" fields, c) greenhouses and d) fields with loamy soils. If possible, untreated soil was collected from a spot outside (50-100 m) the trial, in the same field or from an adjacent field. This was done for the Lelystad, Oosternijkerk, Vredepeel and Creil fields. For the Smilde trial field, no untreated soil was available. The six greenhouse soils were chosen for sampling because frequent application of high rates of metham-sodium (up to 600 kg/ha) could have induced microbial adaptation, resulting in enhanced transformation. Three heavier loam soils were collected in the young polder East Flevoland.At each location, soil sample was collected from 15 sites (0-20 cm layer).The total mass of soil sample was mired thoroughly and then stored in a moist condition in partly open plastic bags at a temperature range of 10-15⁰C in the dark. Incubation of the soil started 2-8 weeks after the collection of soil sample. Glass flask (300 ml) was used as a test vessel for the study. The test vessel glass flask was stoppered with Mininert gas sampling valves. Metham-sodium(3.75 mg) was added to two flasks in 1 cm3 of a diluted aqueous solution of the trade product AAmonam GC (a.i., 510 g/litre).This dose is equivalent to 2.12 mg methyl isothiocyanate at complete conversion.The flasks were placed in the dark in a water bath at 15 (± 0.2) "C and were occasionally shaken to ensure quick equilibration of methyl isothiocyanate between the gas, water and solid phases. From 0.1 d on, up to 15 d the headspace of the flasks was sampled after increasing intervals by withdrawing a 0.1-0.5 ml sample with a 1 ml gas syringe.At the sampling times the remaining masses of methyl isothiocyanate were calculated. The masses were expressed as a fraction{%)of the dose of methyl isothiocyanate, or of the theoretical dose for the flasks to which metham-sodium had been added. The soils were extracted with ethyl acetate (100 ml) and water (50 ml) by shaking for 2 h on a reciprocating shaker. Part of the supernatant organic layer was pipetted off and dried with anhydrous sodium sulphate. Recovery for each soil type was calculated from the amounts extracted from two flasks after incubation for 0.1-0.2 d. Recovery for all soils ranged from93-102%of the dose. No corrections were made for this recovery. Headspace samples (0.1-0.5 ml) were injected directly into the gas chromatograph. At each sampling time, two samples were taken, which always gave similar results (mean difference 3 % of the mean concentration).Methyl isothiocyanate was determined to be the transformation product of the test chemicalMetam-sodium. Thus, concentrations of methyl isothiocyanate in the ethyl acetate extracts and in the headspace samples were measured with a Pye Unicam GCV gas chromatograph equipped with a flame photometer detector, operated in the sulphur mode (394 nm filter). The glass column (length 1.4 m; inner diameter 4 mm) was packed with 3% Carbowax 20 M on Chromosorb W AW-DMCS, particle size 0.15-0.18 mm. At a carrier gas (nitrogen) flow rate of 60 ml min~* and a column temperature of 110 °C, the retention time of methyl isothiocyanate was 1 min. The temperatures of injector and detector were 150 and 210°C .respectively. Concentrations in the extracts and headspace samples were calculated with the external standard method, based on peak heights or integrated peak areas obtained with 3 pi injections of standard solutions of methyl isothiocyanate (99.8%)in ethyl acetate(0.1-10mg/litre).The transformation of metham-sodium to methyl isothiocyanate at 15°C was very fast in most soils. The highest rates were found for the three loamy soils (Topper, Geerlig, Westerdijk) the Meijer "problem" soil and the Vellekoop greenhouse soil. In these soils, the highest concentrations of methyl isothiocyanate were already measured at the first sampling, 0.1 d after addition ofmetham-sodium. In the other humic and sandy soils, with lower pH, the highest concentrations of methyl isothiocyanate were measured at the second and third sampling, 0.3 and 1 d respectively after application of the metham-sodium. In the Odoorn soil maximum, concentration was measured after 4 d, which Indicated a slow transformation for part of the metham-sodium.The maximum amount of methyl isothiocyanate measured in the incubation flasks depends on the ratio between the rates of formation and transformation of methyl isothiocyanate in the soils.Therefore, the extent to which metham-sodium was transformed to methyl isothiocyanate was estimated wherein the amounts of methyl isothio'cyanate on each sampling time were plotted on a logarithmic scale against time. The amounts of methyl isothiocyanate produced were estimated by linear back extrapolation and found to be more than 90%(90-98) of the amount that could theoretically be produced.The percentage degradation of test chemicalMetam-sodiumin soil was determined to be >90% in 0.1 days (2.4 hrs). The major transformation of the test chemical was determined to bemethyl isothiocyanate and the amounts of methyl isothiocyanate produced were estimated by linear back extrapolation and found to be more than 90%(90-98) of the amount that could theoretically be produced.Thus, based on percentage degradation, it is concluded that the chemicalMetam-sodiumis not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

Additional information

Biodegradation in water

Experimental study for the target compound Metam-sodium (CAS No. 137-42-8) and various supporting studies for its structurally and functionally similar read across substance were reviewed for the biodegradation end point which are summarized as below:

 

In an experimental key study from secondary source (IUCLID dataset, 2000), biodegradation experiment was conducted for 20 days for evaluating the percentage biodegradability of test substance Metam-sodium (CAS no. 132-87-6). The study was performed according to Zahn-Wellens method under aerobic conditions. Activated sludge (not adapted) was used as a test inoculum for the study. Initial test substance conc. used in the study was 200 mg/l based on TOC removal, respectively.The initial TOC concentration after 3 hours was -21%.The percentage degradation of test substance Metam-sodium was determined to be 1, 8, 84 and 77% by DOC removal or COD parameter parameter in 20 days. Thus, based on percentage degradation, Metam-sodium is considered to be readily biodegradable in water.

 

In a supporting study from authoritative database (HSDB and PubChem, 2017) for the read across chemical 1,2-Ethanediylbiscarbamodithioic acid disodium salt (CAS no. 142-59-6), biodegradation experiment was conducted for evaluating the percentage biodegradability of read across substance 1,2-Ethanediylbiscarbamodithioic acid disodium salt (CAS no. 142-59-6). The study was performedunder aerobic conditions using activated sludge as a test inoculum. Test chemical conc. used for the study were 9.8, 10.2, 9.6 and 9.8 mg/l, respectively. Test chemical was fed over four consecutive days to a bench scale activated sludge unit at a conc. of 3 liters synthetic sewage per day. The percentage degradation of test substance1,2-Ethanediylbiscarbamodithioic acid disodium salt was determined to be 96% after a 1 day period. Thus, based on percentage degradation, 1,2-Ethanediylbiscarbamodithioic acid disodium salt is considered to be readily biodegradable in nature.

 

For the read across chemical ammonium N-methyldithiocarbamate (CAS no. 39680-90-5), biodegradation study was conducted for 28 days for evaluating the percentage biodegradability of read across substance ammonium N-methyldithiocarbamate (CAS no. 39680-90-5). Activated sludge was used as a test inoculums for the study. Concentration of inoculum i.e, sludge used was 30 mg/l and initial test substance conc. used in the study was 100 mg/l, respectively. The percentage degradation of test substance ammonium N-methyldithiocarbamate was determined to be 2-13, 41 and 73-87% by BOD, O2 consumption, TOC removal, Test material analysis and HPLC parameter in 28 days. Thus, based on percentage degradation (73-87%), ammonium N-methyldithiocarbamate is considered to be readily biodegradable in nature.

 

On the basis of above results for target chemical Metam-sodium (from secondary source IUCLID dataset, 2000) and for its read across substance (from authoritative database HSDB and PubChem, 2017), it can be concluded that the test substance Metam-sodium can be expected to be readily biodegradable in nature.

Biodegradation in water and sediment

Estimation Programs Interface (EPI Suite, 2018) prediction model was run to predict the half-life in water and sediment for the test compound Metam-sodium (CAS No. 137 -42 -8). If released in to the environment, 21.2% of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of Metam-sodium in water is estimated to be 15 days (360 hrs). The half-life (15 days estimated by EPI suite) indicates that the chemical is not persistent in water and the exposure risk to aquatic animals is moderate to low whereas the half-life period of Metam-sodium in sediment is estimated to be 135 days (3240 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.0899%), indicates that Metam-sodium is not persistent in sediment.

Biodegradation in soil

Various experimental studies for the target chemical Metam-sodium (CAS No. 137-42-8) were reviewed for the biodegradation in soil end point which are summarized as below:

 

In an experimental key study from peer reviewed journal (J.H. Smelt, et. al; 1989), biodegradation experiment in soil was conducted for determining the half-life of the chemical Metam-sodium (CAS no. 137-42-8).Soils for the transformation studies were collected from: a) field trials, b) "problem" fields, c) greenhouses and d) fields with loamy soils. If possible, untreated soil was collected from a spot outside (50-100 m) the trial, in the same field or from an adjacent field. This was done for the Lelystad, Oosternijkerk, Vredepeel and Creil fields. For the Smilde trial field, no untreated soil was available. The six greenhouse soils were chosen for sampling because frequent application of high rates of metham-sodium (up to 600 kg/ha) could have induced microbial adaptation, resulting in enhanced transformation. Three heavier loam soils were collected in the young polder East Flevoland. At each location, soil sample was collected from 15 sites (0-20 cm layer).The total mass of soil sample was mired thoroughly and then stored in a moist condition in partly open plastic bags at a temperature range of 10-15⁰C in the dark. Incubation of the soil started 2-8 weeks after the collection of soil sample. Glass flask (300 ml) was used as a test vessel for the study. The test vessel glass flask was stoppered with Mininert gas sampling valves. Metham-sodium(3.75 mg) was added to two flasks in 1 cm3 of a diluted aqueous solution of the trade product Amonam GC (a.i., 510 g/litre).This dose is equivalent to 2.12 mg methyl isothiocyanate at complete conversion. The flasks were placed in the dark in a water bath at 15 (± 0.2) "C and were occasionally shaken to ensure quick equilibration of methyl isothiocyanate between the gas, water and solid phases. From 0.1 d on, up to 15 d the headspace of the flasks was sampled after increasing intervals by withdrawing a 0.1-0.5 ml sample with a 1 ml gas syringe.At the sampling times the remaining masses of methyl isothiocyanate were calculated. The masses were expressed as a fraction{%)of the dose of methyl isothiocyanate, or of the theoretical dose for the flasks to which metham-sodium had been added. The soils were extracted with ethyl acetate (100 ml) and water (50 ml) by shaking for 2 h on a reciprocating shaker. Part of the supernatant organic layer was pipetted off and dried with anhydrous sodium sulphate. Recovery for each soil type was calculated from the amounts extracted from two flasks after incubation for 0.1-0.2 d. Recovery for all soils ranged from93-102%of the dose. No corrections were made for this recovery. Headspace samples (0.1-0.5 ml) were injected directly into the gas chromatograph. At each sampling time, two samples were taken, which always gave similar results (mean difference 3 % of the mean concentration).Methyl isothiocyanate was determined to be the transformation product of the test chemical Metam-sodium. Thus, concentrations of methyl isothiocyanate in the ethyl acetate extracts and in the headspace samples were measured with a Pye Unicam GCV gas chromatograph equipped with a flame photometer detector, operated in the sulphur mode (394 nm filter). The glass column (length 1.4 m; inner diameter 4 mm) was packed with 3% Carbowax 20 M on Chromosorb W AW-DMCS, particle size 0.15-0.18 mm. At a carrier gas (nitrogen) flow rate of 60 ml min~* and a column temperature of 110 °C, the retention time of methyl isothiocyanate was 1 min. The temperatures of injector and detector were 150 and 210°C .respectively. Concentrations in the extracts and headspace samples were calculated with the external standard method, based on peak heights or integrated peak areas obtained with 3 pi injections of standard solutions of methyl isothiocyanate (99.8%)in ethyl acetate(0.1-10mg/litre).The transformation of metham-sodium to methyl isothiocyanate at 15°C was very fast in most soils. The highest rates were found for the three loamy soils (Topper, Geerlig, Westerdijk) the Meijer "problem" soil and the Vellekoop greenhouse soil. In these soils, the highest concentrations of methyl isothiocyanate were already measured at the first sampling, 0.1 d after addition of metham-sodium. In the other humic and sandy soils, with lower pH, the highest concentrations of methyl isothiocyanate were measured at the second and third sampling, 0.3 and 1 d respectively after application of the metham-sodium. In the Odoorn soil maximum, concentration was measured after 4 d, which Indicated a slow transformation for part of the metham-sodium. The maximum amount of methyl isothiocyanate measured in the incubation flasks depends on the ratio between the rates of formation and transformation of methyl isothiocyanate in the soils. Therefore, the extent to which metham-sodium was transformed to methyl isothiocyanate was estimated wherein the amounts of methyl isothio'cyanate on each sampling time were plotted on a logarithmic scale against time. The amounts of methyl isothiocyanate produced were estimated by linear back extrapolation and found to be more than 90%(90-98) of the amount that could theoretically be produced.The percentage degradation of test chemical Metam-sodium in soil was determined to be >90% in 0.1 days (2.4 hrs). The major transformation of the test chemical was determined to bemethyl isothiocyanate and the amounts of methyl isothiocyanate produced were estimated by linear back extrapolation and found to be more than 90%(90-98) of the amount that could theoretically be produced. Thus, based on percentage degradation, it is concluded that the chemicalMetam-sodiumis not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

Another biodegradation study in soil was carried out for determining the half-life or percentage degradation of the test chemical Metam-sodium (CAS no. 137-42-8) (Stephen B. Pruett, et. al; 2001).The percentage degradation of test chemical Metam-sodium in soil was determined to be92% in less than 12 days. Transformation product of chemical Metam-sodium was determined to be methylisothiocyanate (MITC) and H2S, respectively. Depending on soil moisture and soil composition, substantial amount of Metam-sodium may remain in the soil for 12 days or more, respectively. Based on this, it is concluded that the chemical Metam-sodium is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

In a supporting study from authoritative database (HSDB and PubChem, 2017), biodegradation experiment in soil was carried out for determining the half-life of the test chemical Metam-sodium (CAS no. 137-42-8).The half-life period of Metam-sodiumin soil was determined to be ranges from 0.23 min to 4 days, respectively. Based on this half-life value of chemical Metam-sodium, it is concluded that the chemical Metam-sodium is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

For the target chemical Metam-sodium (CAS no. 137-42-8) from authoritative database (Agricultural Research Service (ARS) Pesticide Properties Database, 1995 and Pesticide Properties in the Environment, 2012), biodegradation study in soil was carried out for determining the half-life of the test chemical Metam-sodium (CAS no. 137-42-8).The half-life period of Metam-sodium in soil was determined to be ranges from 5 to 7 days, respectively. Based on this half-life value of chemical Metam-sodium, it is concluded that the chemical Metam-sodium is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

Additional biodegradation study from secondary source (IUCLID dataset, 2000) in soil was carried out for determining the half-life of the test chemical Metam-sodium (CAS no. 137-42-8).The study was performed according to other method EPA/FIFRA 162–1at a temperature of 28°C, respectively. Test chemical used for the study was in the form of radiolabel 14C–sodium–monomethyldithiocarbamate. Initial test substance concentration used for the study was 125.7 mg/l. The properties of the soil includes clay 1.2%, silt 7%, sand 91.8%, organic carbon content 0.2%, pH 6.9 and CEC of the soil was6.5 meq/100 g soil dry weight, respectively. 6.5 meq/100 g soil dry weight. The half-life period ofMetam-sodiumin soil was determined to be 23 min, respectively. Based on this half-life value of chemical Metam-sodium, it is concluded that the chemical Metam-sodium is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

In a supporting study, biodegradation experiment in soil was carried out for determining the half-life of the test chemical Metam-sodium (CAS no. 137-42-8) (HSDB, PubChem and Pesticide Properties Database, 2017).The half-life period of Metam-sodium in soil was determined to be 7 days. Based on this half-life value of chemical Metam-sodium, it is concluded that the chemical Metam-sodium is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

In an another study from authoritative database (AGRITOX - Plant Protection Phentopharmaceuticals Database, 2012), biodegradation experiment in soil was carried out under aerobic conditions for 21 days for determining the percentage degradation of the chemical Metam-sodium (CAS no. 137-42-8).The percentage degradation of test chemical Metam-sodium in soil was determined to be in the range 45.96 – 86.25% in 21 days. The transformation of the product of the test chemical was determined to be methylisothiocyanate (MITC). The max. metabolite i.e methylisothiocyanate 82.9% was obtained in 1-2 days.Based on this, it is concluded that the chemical Metam-sodium is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

On the basis of above results for target chemical Metam-sodium (from peer reviewed journal, secondary source and authoritative databases), it can be concluded that the test substance Metam-sodium is not persistent in the soil environment and therefore the exposure risk to soil dwelling animals is moderate to low.

On the basis of available information, the test substance 1,4-Dibromobutane can be considered to be readily biodegradable in nature