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Biodegradation in water

Estimation Programs Interface Suite (EPI suite, 2017) was run to predict the biodegradation potential of the test compound 2-hydroxy-p-toluic acid (CAS no. 50 -85 -1) in the presence of mixed populations of environmental microorganisms. The biodegradability of the substance was calculated using seven different models such as Linear Model, Non-Linear Model, Ultimate Biodegradation Timeframe, Primary Biodegradation Timeframe, MITI Linear Model, MITI Non-Linear Model and Anaerobic Model (called as Biowin 1-7, respectively) of the BIOWIN v4.10 software. The results indicate that chemical 2-hydroxy-p-toluic acid is expected to be readily biodegradable.

readily biodegradable in nature.

Biodegradation in water and sediment

Estimation Programs Interface (EPI Suite, 2017) prediction model was run to predict the half-life in water and sediment for the test compound 2-Hydroxy-4-methylbenzoic acid (CAS No. 50 -85 -1). If released in to the environment, 26 % of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of test chemical 2-Hydroxy-4- methylbenzoic acid in water is estimated to be 15 days (360 hrs). The half-life (15 days estimated by EPI suite) indicates that the chemical 2-Hydroxy-4-methylbenzoic acid is not persistent in water and the exposure risk to aquatic animals is moderate to low whereas the half-life period of test chemical 2-Hydroxy-4-methylbenzoic acid 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 0.0853 %), indicates that test chemical 2-Hydroxy-4-methylbenzoic acid is not persistent in sediment.  

Biodegradation in soil

The half-life period of test chemical 2-Hydroxy-4-methylbenzoic acid (CAS No. 50 -85 -1) in soil was estimated using Level III Fugacity Model by EPI Suite version 4.1 estimation database (EPI suite, 2017). If released into the environment, 73.7% of the chemical will partition into soil according to the Mackay fugacity model level III. The half-life period of test chemical 2-Hydroxy-4-methylbenzoic acid in soil is estimated to be 30 days (720 hrs). Based on this half-life value of test chemical 2-Hydroxy-4-methylbenzoic acid, it is concluded that the chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

Additional information

Biodegradation in water

One predicted data study and one experimental study for target chemical and five experimental studies for its structurally similar read across chemical have been conducted for biodegradation in water endpoint and results of all the studies are summarized below.

The predicted data study for target chemical was done by using Estimation Programs Interface Suite (EPI suite, 2017) to estimate the biodegradation potential of the test compound 2-hydroxy-p-toluic acid (CAS no. 50 -85 -1) in the presence of mixed populations of environmental microorganisms. The biodegradability of the substance was calculated using seven different models such as Linear Model, Non-Linear Model, Ultimate Biodegradation Timeframe, Primary Biodegradation Timeframe, MITI Linear Model, MITI Non-Linear Model and Anaerobic Model (called as Biowin 1-7, respectively) of the BIOWIN v4.10 software. The results indicate that chemical 2-hydroxy-p-toluic acid is expected to be readily biodegradable.

Another study was experimental study done from peer reviewed journal Applied and Environmental Microbiology, (Kathleen L. Londry et. al; 1997) and secondary source (Kathleen Louise Londry, 1997) in this study biodegradation experiment was conducted for evaluating the percentage biodegradability of test substance 2-Hydroxy-4-methylbenzoic acid (CAS no. 50-85-1) under anaerobic conditions at a temperature of 32°C .Desulfotomaculumsp. strain Groll (bacteria) was used as a test inoculum obtained from the Deutsche Sammlung von Mikroorganismen, Braunschweig, Germany (catalog no. 7213). Initial test substance conc. used in the study was 76.07 mg/l (500µM).The organism was cultivated in an anaerobic medium but with only 1 mM sulfide as the reductant. Strain Groll was incubated at 32°C in the dark without shaking. Cultures were maintained by periodically adding substrate (250mM) and by repeated transfer. The cultures were amended by addition of substrates from neutralized, sterile, anoxic stock solutions. Test was performed in an anaerobic chamber which was sealed with butyl rubber stoppers and aluminum crimp seals. The headspace of each vessel was then changed to N2-CO2 (80 : 20). The degradation of test substance was tested in the anaerobic medium and inoculated (10% vol/vol) with a culture of strain Groll. Degradation was monitored by following the depletion of test compound over time. Sterile controls were also setup during the study. Samples of culture fluid were withdrawn under strictly anaerobic and aseptic conditions and stored frozen until analyzed. Concentrations of test compound 2 -Hydroxy-4 -methylbenzoic acid were determined by HPLC. The percentage degradation of test substance 2 -Hydroxy-4 -methylbenzoic acid was determined to be 0% by HPLC parameter. Thus, based on percentage degradation, 2 -Hydroxy-4 -methylbenzoic acid is considered to be not readily biodegradable in nature.

Next experimental study was done for read across chemical salicylic acid (CAS no. 69-72-7) from Journal of Hazardous Materials (1986) in this study the biodegradability of read across chemical salicylic acid was determined, by using electrolytic respirometer in aerobic condition. The study was calculated for 14 days, at temperature 20 °C in neutral medium (pH-7).The biodegradability of read across chemical salicylic acid was calculated, as the 50% of salicylic acid was biodegrades in 7.5 to 9.5 hrs only. Result indicated that the read across chemical salicylic acid is readily biodegradable in water.

 

Another experimental study was done from authoritative database (J check, 2016) in this study biodegradation experiment was conducted for 28 days for evaluating the percentage biodegradability of read across substance Aspirin (CAS no. 50-78-2). Concentration of inoculum i.e, sludge used was 30 mg/l and initial read across substance conc. used in the study was 100 mg/l, respectively. At the beginning of the test, the pH of the test solution was adjusted. The read across substance was hydrolyzed to form Salicylic acid and Acetic acid in (Water + Test Substance) systems. The percentage degradation of read across substance was determined to 86%, 97% and 100% by BOD, TOC removal and HPLC parameter in 28 days. Thus, based on percentage degradation, Aspirin is considered to be readily biodegradable in nature.

Next experimental study was done for read across substance 2-methoxybenzoic acid (CAS no. 579-75-9) from Environmental Toxicology and Chemistry journal (2003) in this study biodegradation experiment was conducted for 5 days for evaluating the percentage biodegradability of read across substance 2-methoxybenzoic acid(CAS no. 579-75-9).The study was performed using the standard iodometric titration method. River water was used as a test inoculum obtained from Jilin section in the Songhua river. Temperature of the water sample was 15-20°C, pH 6.8 – 7.0 and dissolved oxygen was ranged between 7.8 – 9.0 mg/l. Initial read across substance conc. used in the study was 2 mg/l on the basis of ThOD. The test chemical was added to 250 ml BOD bottles. One milliliter of diluted water sample was cultivated in 15 ml of medium at 31°C for 24 h, and the number of colonies was enumerated as the bacterial counts. The bottles were then filled to capacity with the water sample, sealed and incubated for 5 days at 20 ± 1°C.Two replicates were conducted for read across chemical and read across control (inoculum only).The DO concentrations were determined by the iodometric titration method. Biodegradability was assessed by measuring the BOD values in milligrams per liter (oxygen uptake values of test compound minus control).Biodegradability was expressed as the first-order kinetic rate constant (K) according to the traditional Monod equation (on the assumption that the bacterial counts were invariable during the experimental period).The total surface area of molecules, the heat of formation (Hf), and the energy of the highest occupied molecular orbital (EHOMO) of read across chemical was calculated by the quantum chemical method Mopac Program. The linear regression analyses were performed with the SPSS® statistical package (Ver 10.0, SPSS, Chicago, IL, USA).An obvious negative correlation apparently exists between Hf and K, that is, the lower the Hf value (-422.08 kj/M), the higher the K value (1.06/d), and thus based on this relationship, read across chemical was considered to be readily biodegradable by river bacteria.

Next study was done from peer reviewed journal “The Science of the Total Environment,” (1995) in this study Biodegradation experiment was conducted for 28 days for evaluating the percentage biodegradability of read across substance Benzoic acid by bacteria as a test inoculum. Seeding bacteria was used as a test inoculum. The seeding bacteria had been cultured in a continuous anaerobic bioreactor at 37 + 1°C. Synthetic sewage, composed of glucose, peptone and corn steap liquor (carbon ratio = 1:1:2), is supplied into the reactor (3.0 g-C/l, 8.0 g-CS./.d). In this culture, > 95% acidic decomposition and > 90% methanogenic decomposition are achieved. A standard test using 50 ml vials (total capacity: 68 ml) was employed. Ten test vials were prepared under the same conditions, and they were set in a water bath at 37°C ± 0.5”C. The original solution was added to the test inoculum and organic medium in oxygen-free water. At the starting time and after every week, two vials were opened simultaneously, and the concentration of organic compound was analyzed. The concentration of organic compound was determined by dissolved organic carbon (DOC).Biodegradation ratio is determined by analyzing the decrease of DOC in the standard test. The percentage degradation of the read across compound was determined to be 101% in 14 days by using standard test. Thus, based on the percentage degradation, the read across chemical Benzoic acid (CAS no.65-85-0) was considered to be readily biodegradable in nature.

Last experimental study was done from Water Pollution Control Federation journal (1976) in this study , Biodegradation experiment was conducted for 30 days for evaluating the percentage biodegradability of read across substance 1,2-Benzenedicarboxylic acid, monopotassium salt (CAS no.877-24-7) . Glucose-glutamic acid mixture was used as a reference substance for the biodegradation study. The results are compared with the chemical oxygen demand (COD) of the read across chemical, which measures its maximum oxygen combining power; the results are also compared with the BOD test performed on a standard glucose-glutamic acid reference solution used for BOD calibration. Reference substance i.e; glucose-glutamic acid mixture consumes 75 percent of its maximum oxygen requirement (COD) within 5 days and almost 100 percent in 30 days. Thus, based on this result, the reference substance is considered to be readily biodegradable. The percentage degradation of read across substance was determined to be 92% by BOD parameter in 30 days. Thus, based on percentage degradation, read across chemical 1,2-Benzenedicarboxylic acid, monopotassium salt was considered to be readily biodegradable in nature.

Thus by considering all the studies mentioned above for target chemical 2-hydroxy-p-toluic acid (CAS no. 50 -85 -1) and its various structurally similar read across chemicals it is observed that predicted data study for target chemical interpret that target chemical is readily degradable but experimental study shows that it is not readily degradable but this result is obtained by using bacteria Desulfotomaculumsp. strain Groll and this bacteria is Gram positive anaerobic bacteria and uses sulfate as terminal electron acceptor which is reduced to sulfide. It is generally found in subsurface biosphere 10-100M below ground or sea bed. Therefore maybe because of all this criteria of this bacteria test chemical is not degraded by using this bacteria and this experiment was also conducted in anerobic condition. It can be possible that target chemical is readily degradable by aerobic condition by different bacteria. This possibility of degradation is supported by various studies of structurally similar read across chemicals as mentioned above from different sources all studies of read across chemical are showing that it is readily degradable. Further according to OECD guidelines degradability of target chemical should be analyzed by using activated sludge or bacteria from soil or water which are easily available in nature and has many different types of bacteria. Therefore on the basis of predicted data of target chemical and its structurally similar read across chemicals it is concluded that target chemical is readily biodegradable in nature.

 

Biodegradation in water and sediment

Estimation Programs Interface (EPI Suite, 2017) prediction model was run to predict the half-life in water and sediment for the test compound 2-Hydroxy-4-methylbenzoic acid (CAS No. 50 -85 -1). If released in to the environment, 26 % of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of test chemical 2-Hydroxy-4- methylbenzoic acid in water is estimated to be 15 days (360 hrs). The half-life (15 days estimated by EPI suite) indicates that the chemical 2-Hydroxy-4-methylbenzoic acid is not persistent in water and the exposure risk to aquatic animals is moderate to low whereas the half-life period of test chemical 2-Hydroxy-4-methylbenzoic acid 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 0.0853 %), indicates that test chemical 2-Hydroxy-4-methylbenzoic acid is not persistent in sediment.  

Biodegradation in soil

The half-life period of test chemical 2-Hydroxy-4-methylbenzoic acid (CAS No. 50 -85 -1) in soil was estimated using Level III Fugacity Model by EPI Suite version 4.1 estimation database (EPI suite, 2017). If released into the environment, 73.7% of the chemical will partition into soil according to the Mackay fugacity model level III. The half-life period of test chemical 2-Hydroxy-4-methylbenzoic acid in soil is estimated to be 30 days (720 hrs). Based on this half-life value of test chemical 2-Hydroxy-4-methylbenzoic acid, it is concluded that the chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

On the basis of available information, the test substance 2-Hydroxy-4-methylbenzoic acid can be considered to be readily biodegradable in nature.