4-hydroxy-6-(methylamino)naphthalene-2-sulphonic acid

Endpoint summary

Description of key information

Biodegradation in water

Biodegradability of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS no. 6259 -53 -6) is predicted using QSAR toolbox version 3.4 (2017) with logKow as the primary descriptor. Test substance undergoes 1.48% degradation by BOD in 28 days. Thus, based on percentage degradation, the test chemical 4 -hydroxy-6 -(methylamino)naphthalene-2 -sulfonic acid was estimated to be not readily biodegradable in water.

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  4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6). If released in to the environment, 13.8% of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of 4 -hydroxy-6 -(methylamino)naphthalene-2 -sulfonic acid in water is estimated to be 37.5 days (900 hrs). The half-life (37.5 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 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid in sediment is estimated to be 337.5 days (8100 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.205%), indicates that 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid is not persistent in sediment.

 

Biodegradation in soil

The half-life period of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6) 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, 86% of the chemical will partition into soil according to the Mackay fugacity model level III. The half-life period of 4 -hydroxy-6 -(methylamino) naphthalene-2 -sulfonic acid in soil is estimated to be 75 days (1800 hrs). Based on this half-life value of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic 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.

Bioaccumulation: aquatic / sediment

BCFBAF model (v3.01) of Estimation Programs Interface (EPI Suite, 2017) was used to predict the bioconcentration factor (BCF) of test chemical 4 -hydroxy-6 -(methylamino) naphthalene-2 -sulfonic acid (CAS No. 6259 -53 -6). The bioconcentration factor (BCF) of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 3.162 L/kg whole body w.w (at 25 deg C) which does not exceed the bio concentration threshold of 2000, indicating that the chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid is not expected to bioaccumulate in the food chain.

Adsorption / desorption

KOCWIN model (v2.00) of Estimation Programs Interface (EPI Suite, 2017) was used to predict the soil adsorption coefficient i.e Koc value of test chemical 4 -hydroxy-6 -(methylamino)naphtha lene-2 -sulfonic acid (CAS No. 6259 -53 -6). The soil adsorption coefficient i.e Koc value of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 260.6 L/kg (log Koc=2.4160)  by means of MCI method (at 25 deg C). This Koc value indicates that the substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid has a low sorption to soil and sediment and therefore have moderate migration potential to ground water.

Additional information

Biodegradation in water

Various predicted data for the target compound 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259-53-6) and supporting weight of evidence studies for its structurally similar read across substance were reviewed for the biodegradation end point which are summarized as below:

 

In a prediction done by SSS (2017) using OECD QSAR toolbox version 3.4 with logKow as the primary descriptor, percentage biodegradability of test chemical4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid(CAS No. 6259-53-6) was estimated.Test substance undergoes 1.48% degradation by BOD in 28 days. Thus, based on percentage degradation, the test chemical4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acidwas estimated to be not readily biodegradable in water.

 

In another prediction using the Estimation Programs Interface Suite (EPI suite, 2017), the biodegradation potential of the test compound4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid(CAS No. 6259-53-6) in the presence of mixed populations of environmental microorganisms was estimated.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 chemical4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acidis expected to be not readily biodegradable.

 

For the read across chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt (CAS no. 2611-82-7) from peer reviewed journal (U. Pagga and O. Brown, 1986), biodegradation study was carried out for 48 days for evaluating the percentage biodegradation of the read across chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt using modified OECD Guideline 302B. Activated sludge was used as a test inoculum. The sources of the activated sludge were treatment plants conveniently located to the laboratories carrying out the test. These treatment plants received communal and/or industrial wastewater. Concentration of inoculum i.e, activated sludge used was 0.5 g/l and initial test substance conc. used in the study was 100 mg/l. Analytical methods involve the measurement of extinction at absorption maximum 412 nm and DOC (dissolved organic carbon).The percentage degradation of substance 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt was determined to be 5% by DOC removal. Based on the limit values for classification of Static Test – the test chemical was classified in CATEGORY ‘D’. Thus, the substance 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt is considered to be not readily biodegradable in nature.

 

Another biodegradation study was conducted for evaluating the percentage biodegradability of read across substance 1,3 -Naphthalenedisulfonic acid, 7 -hydroxy-8 -((4 -sulfo-1 -naphthalenyl)azo)-, trisodium salt (CAS no. 2611 -82 -7) (Toshihide Saito et. al, 1984). Activated sludge was used as a test inoculum obtained from municipal sewage. Test substance of conc. 500 mg/l was prepared and diluted as needed. The COD measurement was performed by the potassium dichromate reflux method based on Japanese Industrial Standards. In the BOD measurement, a sample solution was taken into a container. Then JIS-BOD testing solutions, i.e. 3 ml of A solution and 1 ml of B, C, D solutions were added to the sample solution, respectively. Then 5 ml of the supernatant of the municipal sewage activated sludge was added to the sample solution and diluted to 300 ml with water. Immediately, the BOD-time curve was recorded at 20~ using an Ohkura OM-200I type coulometer. The TOC measurement was carried out by a Yanagimoto TOC-ILW.BOD5, COD, ThOD and TOC value of the test chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt was determined to be 0.021, 0.65, 1.23 and 0.20 g/g, respectively. The BOD5/TOC ratio of chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt was determined to be 0.11 (i.e. ranges in between 0.08-0.89), indicating that the chemical is highly resistant to aerobic biodegradation. Thus, based on this value BOD5/TOC value, it can be concluded that the chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt is not readily biodegradable in nature.

 

In a supporting weight of evidence study from authoritative database (J-CHECK, 2017) and secondary source (HPVIS and OECD SIDS) for the read across chemical calcium 3-hydroxy-4-[(4-methyl-2-sulfonatophenyl)diazenyl]-2-naphthoate (CAS no. 5281-04-9), biodegradation experiment was conducted for 28 days for evaluating the percentage biodegradability of read across substance calcium 3 -hydroxy-4 -[(4 -methyl-2 -sulfonatophenyl)diazenyl]-2 -naphthoate (CAS no. 5281 -04 -9). The study was performed according to OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I) under aerobic conditions. Activated sludge (non-adapted) 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 substance calcium 3 -hydroxy-4 -[(4 -methyl-2 -sulfonatophenyl)diazenyl]-2 -naphthoate was determined to be 10 and 0% by BOD and HPLC parameter in 28 days. Thus, based on percentage degradation, calcium 3-hydroxy-4-[(4-methyl-2-sulfonato phenyl)diazenyl]-2-naphthoate is considered to be not readily biodegradable in nature.

 

On the basis of above results for target chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (from OECD QSAR toolbox version 3.4 and EPI suite, 2017) and for its read across substance (from peer reviewed journals, authoritative database J-CHECK and secondary source HPVIS & OECD SIDS), it can be concluded that the test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid can be expected to be not 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  4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6). If released in to the environment, 13.8% of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of 4 -hydroxy-6 -(methylamino)naphthalene-2 -sulfonic acid in water is estimated to be 37.5 days (900 hrs). The half-life (37.5 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 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid in sediment is estimated to be 337.5 days (8100 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.205%), indicates that 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid is not persistent in sediment.

 

Biodegradation in soil

The half-life period of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6) 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, 86% of the chemical will partition into soil according to the Mackay fugacity model level III. The half-life period of 4 -hydroxy-6 -(methylamino) naphthalene-2 -sulfonic acid in soil is estimated to be 75 days (1800 hrs). Based on this half-life value of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic 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 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid can be considered to be not readily biodegradable in nature.

Bioaccumulation: aquatic / sediment

Various predicted data for the target compound 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259-53-6) and supporting weight of evidence study for its structurally similar read across substance were reviewed for the bioaccumulation end point which are summarized as below:

 

In aprediction done using theBCFBAF Program(v3.01) of Estimation Programs Interface (EPI Suite, 2017) was used to predict the bioconcentration factor (BCF) of test chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6). The bioconcentration factor (BCF) of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 3.162 L/kg whole body w.w (at 25 deg C).

 

In an another prediction done by using Bio-concentration Factor (v12.1.0.50374) moduleACD (Advanced Chemistry Development)/I-Lab predictive module, 2017), theBio-concentration Factor (BCF) over the entire pH scale (pH 1 -14) of the test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS no. 6259 -53 -6) was estimated to be 1.

 

Bioconcentration Factor (BCF) of test chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated using Chemspider database(ChemSpider, 2017). The bioconcentration factor of test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 1 at both pH 5.5 and 7.4, respectively.

 

Another predicted data was estimated usingSciFinder database (American Chemical Society (ACS), 2017) was used for predicting the bioconcentration factor (BCF) of test chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6).The bioconcentration factor (BCF) of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 1 (at 25 deg C).

 

From CompTox Chemistry Dashboard using OPERA (OPEn (quantitative) structure-activity Relationship Application)  V1.02 model in which calculation based on PaDEL descriptors (calculate molecular descriptors and fingerprints of chemical), the bioaccumulation i.e BCF for test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 4.89 dimensionless . The predicted BCF result based on the 5 OECD principles. Thus based on the result it is concluded that the test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid is non-bioaccumulative in nature.

 

In a supporting weight of evidence study from authoritative database (J-CHECK, 2017) for the read across chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt (CAS no. 2611-82-7),bioaccumulation experiment was conducted on test organism Cyprinus carpio for 28 days for evaluating the bioconcentration factor (BCF value) of read across chemical 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt. The study was performed according to other guideline "Bioaccumulation test of a chemical substance in fish or shellfish" provided in "the Notice on the Test Method Concerning New Chemical Substances". Cyprinus carpio was used as a test organism for the study. Details on analytical methods involve the recovery ratio: Test water: 100% (The test solution were input analytical equipment directly), Fish: 82.4%, - Limit of quantitation: Test water: 1st concentration area : 21µg/l, 2nd concentration area : 2.1µg/l, Fish: 260 ng/g. Test chemical nominal conc. used for the study were 0.474mg/land 0.0474 mg/l, respectively. Range finding study involve the LC50 (96 hr) > 200 mg/l onRice fish (Oryzias latipes).The bioconcentration factor (BCF value) of substance 1,3-Naphthalenedisulfonic acid, 7-hydroxy-8-((4-sulfo-1-naphthalenyl)azo)-, trisodium salt on Cyprinus carpio was determined to be ≤ 0.55 L/Kg at a conc. of 0.474 mg/l and ≤ 5.6 L/Kg at a conc. of 0.0474 mg/l, respectively.

 

Another bioaccumulation study was conducted for estimating the BCF (bioaccumulation factor) value of read across chemical 1,3 -Naphthalenedisulfonic acid, 7 -hydroxy-8 -((4 -sulfo-1 -naphthalenyl)azo)-, trisodium salt (CAS no. 2611 -82 -7) (HSDB, 2017). The bioaccumulation factor (BCF) value was calculated using a measured water solubility of 80,000 mg/l and a recommended regression-derived equation. The estimated BCF (bioaccumulation factor) value of 1,3 -Naphthalenedisulfonic acid, 7 -hydroxy-8 -((4 -sulfo-1 -naphthalenyl)azo)-, trisodium salt was determined to be 1.0 dimensionless.

 

For the read across chemical calcium 3-hydroxy-4-[(4-methyl-2-sulfonatophenyl)diazenyl]-2-naphthoate (CAS no. 5281-04-9) from authoritative database (J-CHECK, 2017) and secondary source (OECD SIDS, 1994),bioaccumulation experiment was conducted on test organism Cyprinus carpiofor 6 weeks for evaluating the bioconcentration factor (BCF value) of read across chemical calcium 3 -hydroxy-4 -[(4 -methyl-2 -sulfonatophenyl)diazenyl]-2 -naphthoate. The study was performed according to OECD Guideline 305 (Bioconcentration: Flow-through Fish Test) and other guideline "Bioaccumulation test of a chemical substance in fish or shellfish" provided in "the Notice on the Test Method Concerning New Chemical Substances", respectively at a temperature of 25°C. Cyprinus carpio was used as a test organism for the study. Test chemical nominal conc. used for the study were 0.3mg/land 0.03 mg/l, respectively. Test chemical solution was prepared in HCO-40 and Crystal sugar. Analytical method involve therecovery ratio: Fish : 79.6 %, - Limit of quantitation : Test water : 1st concentration area : 0.017 microg/mL, 2nd concentration area : 0.00 microg/mL, Fish : 0.18 microg/g.Range finding study involve theLC50(48h) >= 50.0 mg/LonRice fish (Oryzias latipes).The bioconcentration factor (BCF value) of substance calcium 3-hydroxy-4-[(4-methyl-2-sulfonatophenyl)diazenyl]-2-naphthoateonCyprinus carpio was determined to be in the range of ≤ 0.7-1.8 L/Kg at a conc. of 0.3 mg/l and ≤ 6.9 L/Kg at a conc. of 0.03 mg/l, respectively.

 

On the basis of above results for target chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (from EPI suite, ACD labs,ChemSpider, Scifinder and CompTox Chemistry Dashboard,  2017) and for its read across substance from authoritative database (HSDB & J-CHECK) and (secondary source OECD SIDS), it can be concluded that the BCF value of test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid ranges from 1 – 4.89 which does not exceed the bioconcentration threshold of 2000, indicating that the chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid is not expected to bioaccumulate in the food chain.

Adsorption / desorption

Various predicted data for the target compound 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259-53-6) and supporting weight of evidence study for its structurally similar read across substance were reviewed for the adsorption end point which are summarized as below:

 

In aprediction done using theKOCWIN Program(v2.00) of Estimation Programs Interface (EPI Suite, 2017) was used to predict the soil adsorption coefficient i.e Koc value of test chemical 4 -hydroxy-6 -(methylamino)naphtha lene-2 -sulfonic acid (CAS No. 6259 -53 -6). The soil adsorption coefficient i.e Koc value of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 260.6 L/kg (log Koc=2.4160)  by means of MCI method (at 25 deg C). This Koc value indicates that the substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid has a low sorption to soil and sediment and therefore have moderate migration potential to ground water.

 

The Soil Adsorption Coefficient i.e Koc value of test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS no. 6259 -53 -6) was estimated using Adsorption Coefficient module (v12.1.0.50374) program as Koc 1 (log Koc = 0) at pH range 1-14 respectively(ACD (Advanced Chemistry Development)/I-Lab predictive module, 2017). This Koc value indicates that the test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid has a negligible sorption to soil and therefore have rapid migration potential to groundwater.

 

In an another prediction done by using ChemSpider Database (2017),the Soil Adsorption Coefficient i.e Koc value of test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS no. 6259 -53 -6) was estimated. The adsorption coefficient (Koc) value of test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 1 (Log Koc = 0 at both pH 5.5 and 7.4, respectively. This Koc value indicates that the test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid has a negligible sorption to soil and therefore have rapid migration potential to groundwater.

 

Additional soil adsorption coefficient i.e Koc value of test chemical4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (CAS No. 6259 -53 -6)was estimated using the SciFinder database (American Chemical Society (ACS), 2017).The soil adsorption coefficient i.e Koc value of 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid was estimated to be 1 (log Koc = 0) (at 25 deg C). This Koc value indicates that the substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid has a negligible sorption to soil and sediment and therefore have rapid migration potential to ground water.

 

In a supporting weight of evidence study from experimental study report (Sustainability Support Services (Europe) AB, Report no. UERL/PC/010-03, 2017) for the read across chemical aluminium, 6-hydroxy-5-[(4-sulfophenyl)azo]-2-naphthalenesulfonic acid complex (CAS No. 15790 -07 -5), the adsorption coefficient Koc in soil and in sewage sludge of read across chemical aluminium, 6-hydroxy-5-[(4-sulfophenyl)azo]-2-naphthalenesulfonic acid complex was determined by the Reverse Phase High Performance Liquid Chromatographic method according to OECD Guideline No. 121 for testing of Chemicals. The solutions of the test substance and reference substances were prepared in appropriate solvents. A test item solution was prepared by accurately weighing 3 mg of test item and diluted with methanol: water (2:3) phase up to 25ml. Thus, the test solution concentration was 120 mg/l. The pH of test substance was 5.44. Each of the reference substance and test substance were analysed by HPLC at 210 nm. After equilibration of the HPLC system, Urea was injected first, the reference substances were injected in duplicate, followed by the test chemical solution in duplicate. Reference substances were injected again after test sample, no change in retention time of reference substances was observed. Retention time tR were measured, averaged and the decimal logarithms of the capacity factors k were calculated. The graph was plotted between log Koc versus log k(Annex - 2).The linear regression parameter of the relationship log Koc vs log k were also calculated from the data obtained with calibration samples and therewith, log Koc of the test substance was determined from its measured capacity factor. The reference substances were chosen according to functional similarity with the test substance and calibration graph prepared. The reference substances were 2-nitrophenol, nitrobenzene, 4-nitrobenzamide, N, N-dimethylbenzamide and Nmethylbenzamide having Koc value ranging from 1.3 to 2.47. The Log Koc value of chemical aluminium, 6-hydroxy-5-[(4-sulfophenyl)azo]-2-naphthalenesulfonic acid complex was determined to be 2.1368 ± 0.0018 at 25°C. This log Koc value indicates that the substance aluminium, 6-hydroxy-5-[(4-sulfophenyl)azo]-2-naphthalenesulfonic acid complex has a low sorption to soil and sediment and therefore have moderate migration potential to ground water.

 

On the basis of above overall results for target chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid (from EPI suite, ACD labs,ChemSpider and Scifinder,2017) and for its read across substance from experimental UERL study report, it can be concluded that the Koc value of test substance 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid ranges from 1–260.6, indicating that the test chemical 4-hydroxy-6-(methylamino)naphthalene-2-sulfonic acid has a negligible to low sorption to soil and sediment and therefore have rapid to moderate migration potential to ground water.