Sodium O-ethyl dithiocarbonate

Endpoint summary

Additional information

Environmental fate and pathways

 

Environmental Fate/Exposure Summary: 

Environmental exposure

SEX is used as a collector during the processing of sulphide ores by flotation, a process that involves addition of the reagent to aqueous slurries ofcrushed and finely ground ore contained in flotation tanks. Air is blown through the slurry. In general, a series of such tanks is used. During the use of SEX in the flotation process the mineral particles become separated as a froth from the tailings, which settle at the bottom of the flotation tank.

The froth (float) is collected and dried, either in air under ambient conditions or atelevatedtemperatures in an oven,while the tailings are conveyed as a slurry to atailings dam where they settle, dry and consolidate. Spills and washings wouldalso be directed to tailings dams. Tailings typically have a solids content of about 30%. In some operations, tailings may be intercepted in settling tanks so thatwastewater containing low concentrations of xanthates can be recovered for reuse inflotation. Xanthates in the tailings are not monitored, but most would be expected to beretained in the froth. Xanthate residues in the ore concentrate are expected to decomposeduring drying or smelting.

 

Environmental fate

Hydrolysis will be a significant factor in determining the environmental fate of Reaction mass of SEX. In neutral or mildly alkaline solutions, SEX decomposes to the alcohol, carbon disulphide,sodium carbonate and sodium trithiocarbonate, the two salts arising from neutralisation of carbon disulphide with the sodiumhydroxide liberated. In more strongly alkaline media,hydrogen sulphide is liberated. However, strongly alkaline conditions are unlikely to be encountered under the conditions of use in the mining industry. The half-life at pH 7 at 25°C is reportedly about 260 hours, increasing to over 500 hours in the pH range 8 to 11.

 

Reaction mass of SEX is hydrolytically unstable when exposed to acidic conditions, reverting rapidly toethyl, carbon disulphide and sodium hydroxide, and therefore will not persist in the acidic environment of tailings dams. If discharged to waterways, the chemical would be likely to persist for at least some days, hydrolysing only slowly in this more neutral environment. However, it is not expected to bioaccumulate in view of its ionic character. SEX is not expected to contaminate the environment where oretailings are confined to wellconstructed tailings dams. Most will be retained on sulphide minerals and destroyed when they are dried after flotation. Minor residues that remain associated with tailings will be destroyed by hydrolysis intailings dams.

 

 

Stability

 

Phototransformation in air

 If released to air, a vapor pressure of 0.00000000395mm Hg at 25 deg C (0.00000000395 mm Hg is equivalent to vapour pressure of 5.26E-007 Pa ) indicates that SEX will exist solely as a vapor in the atmosphere. Vapor-phase Reaction mass of SEX will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 1.733 days, calculated from its rate constant of 6.1734 E-12 cm3/molecule-sec at 25 deg.

Xanthates do not contain chromophores that absorb at wavelengths >290 nm and therefore SEX is not expected to be susceptible to direct photolysis by sunlight.

 

Using the AOPWIN QSAR model, the photochemical degradation rate of SEX in the atmosphere is 6.1734 E-12 cm3/molecule-sec, with a resultant predicted half live of 20.791 Hrs ( 1.733 Days (12-hr day; 1.5E6 OH/cm3)

 OVERALL OH Rate Constant = 6.1734 E-12 cm3/molecule-sec

HALF-LIFE = 1.733 Days (12-hr day; 1.5E6 OH/cm3)

HALF-LIFE = 20.791 Hrs

 

Phototransformation in water

It is not applicable for a compound wich dissociates.

When water is added to SEX it reacts with water to form the others substances: alcohol, Sodium carbonate, trithiocarbonate and carbon disulphide because of its high water solubility.

Phototransformation in soil

If released to soil, SEX is expected to have very high mobility based upon an estimated Koc of 4. Volatilization from moist soil surfaces is not expected to be an important fate process.

Therefore testing for Phototransformation in soils does not need to be performed.

 

Hydrolysis

 

Hydrolysis is a chemical reaction during which molecules of water (H2O) are split into hydrogen cations (H+, conventionally referred to as protons) and hydroxide anions (OH−) in the process of a chemical mechanism).

 

When water is added to SEX it reacts with water to form the others substances: alcohol, Sodium carbonate, trithiocarbonate and carbon disulphide.

 

On this basis, SEXdoes not have a potential for Hydrolysis and Sodium ion will not hydrolise.

 

On the other basis hydrolysis may proceed with the others active substances:

 Further hydrolysis of Sodium trithiocarbonate to Sodium carbonate and hydrogen sulphide and carbon disulphide to carbon dioxide and hydrogen sulphide may occur. The reaction is catalysed by the alcohol formed from the xanthic acid and is self accelerating.

 

On this basis hydrolysis proceedwith the others active substances: Sodium trithiocarbonate, carbon disulphide, hydrogen sulphide.

 

Xanthates decompose in aqueous solution by dissociation, oxidation and hydrolysis. Hydrolytic decomposition is the main reaction in alkaline solutions while the other two reactions occur in acidic solutions.

 

Aqueous solution

There are three decomposition pathways of xanthates in aqueous solution:

A. Xanthates dissociate forming alkali metal cations and xanthate anions. The solution undergoes further hydrolysis to xanthic acid which decomposes into carbon disulphide and alcohol.

ROCS2Na + H2O → ROCS2H + NaOH

 

ROCS2H → CS2 + ROH

 

B. Xanthate is oxidised to dixanthogen. The extent of this reaction is very small and dependent on the pH. Equilibrium is reached after about 5–10% of the xanthate is oxidised, and the reaction increases with a fall in the pH.

 

2ROCS–2 + H2O + _O2 →(ROCS2)2 + 2OH–

 

C. In neutral and alkaline media, xanthates decompose by hydrolytic decomposition.

6ROCS–2 + 3H2O →6ROH + CO3 2 – + 3CS2 + 2CS3 2 –

Further hydrolysis of Sodium trithiocarbonate to sodium carbonate and hydrogen sulphide and carbon disulphide to carbon dioxide and hydrogen sulphide may occur. The reaction is catalysed by the alcohol formed from the xanthic acid and is self accelerating.

 

Reaction C is the main reaction in alkaline solution while A and B occur in acidic solutions. During use in mining processes, reaction C is the principal decomposition pathway and carbon disulphide the principal decomposition product.

Part of the carbon disulphide formed may decompose further to carbonate and thiocarbonate salts, some of it may evaporate and some may build up in the xanthate solution. Once the solubility of carbon disulphide is exceeded it forms a separate layer below the Reaction mass of SEX solution.

Reactions A and B are minor and require acidic conditions. Reaction C proceeds in neutral or alkaline pH and is self-accelerating, as it is catalysed by the alcohol formed as a product. Its rate increases with concentration of the reagents and with temperature, from 1.1%/day at 20 °C to 4.6%/day at 40 °C for a 10% solution at pH=10. A decrease in pH from 10 to 6.5 increases the decomposition rate from 1.1%/day to 16%/day. Decomposition is also accelerated by the presence of metals, such as copper, iron, lead or zinc, which act as a catalyst.

 

 

Biodegradation

Biodegradation in water: screening tests

 

When water is added to SEX it reacts with water to form the others substances: alcohol, sodiumcarbonate, trithiocarbonate and carbon disulphide.

Carbon disulphide (CAS number 75–15–0) it is the major decomposition product, which is liquid and have to be considered.

The biodegradation of CS2 was >80 % after 28 days of exposure, therefore CS2 is readily biodegradable. SEX readily decomposes to carbon disulphide, especially in the presence of moisture/water.

Therefore, the Biodegradation in water of carbon disulphide (CS2) need to be considered in the assessment of Reaction mass of SEX.

The biodegradation of Ethyl Alcohol was >60 % after 10 days of exposure, therefore Ethyl Alcohol is readily biodegradable. Reaction mass of SEX readily decomposes to ethyl Alcohol, especially in the presence of moisture/water. Ethyl Alcohol is both reagents used in the manufacture, as well as decomposition products.

Therefore, the Biodegradation in water of Ethyl Alcohol need to be considered in the assessment of Reaction mass of SEX. These results suggest that Reaction mass of SEX will be readily biodegradable and it is not expected to persist in the environment.

These results suggest that SEX will be readily biodegradable and it is not expected to persist in the environment.

 

  

Biodegradation in water and sediment: simulation tests

 

SEX readily decomposes to carbon disulphide, especially in the presence of moisture/water. Therefore, the Biodegradation in water of carbon disulphide (CS2) need to be considered in the assessment of SEX.

Due to their structural similarity, it is expected that all xanthates would have similar Biodegradation effects either due to the xanthate or carbon disulphide.

On this basis, testing for Biodegradation in water for SEX is not applicable

Carbon disulphide (CAS number 75–15–0) it is the major decomposition product, which is liquid and have to be considered.

According to “ANNEX IX- STANDARD INFORMATION REQUIREMENTS FOR SUBSTANCES MANUFACTURED OR IMPORTED IN QUANTITIES OF 100 TONNES OR MORE”, a simulation testing on ultimate degradation in surface water, the study does not need to be performed if the substance is ready biodegradable. As Sodium ethyl xanthate is ready biodegradable a ready biodegradability study does not need to be conducted.

Therefore testing for Biodegradation in water does not need to be performed.

 

 Biodegradation in soil

 

If released to soil, SEX is expected to have very high mobility based upon an estimated Koc of 4. Volatilization from moist soil surfaces is not expected to be an important fate process.

Therefore testing for biodegradation in soil does not need to be performed.

 Bioaccumulation

  

This substance has a limited potential to bioaccumulate (based on log Kow used :, Log Kow estimated : 0.87 , and predicted bioconcentration factors, log BCF = 0.5 (EPIWIN/BCF Program).

The estimated BCF of 3.162 L/kg wet-wt was measured by calculation from EPI SuiteTM v4.1 Program.

These values would suggest very low bioaccumulation potential. This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency).

SMILES : S=C(S([Na]))OCC

CHEM : Carbonodithioic acid, O-ethyl ester, sodium salt

MOL FOR: C3 H5 O1 S2 Na1

MOL WT : 144.18

--------------------------------- BCFBAF v3.01 --------------------------------

                                       Summary Results:

Log BCF (regression-based estimate): 0.50 (BCF = 3.16 L/kg wet-wt)

Biotransformation Half-Life (days) : 0.0426 (normalized to 10 g fish)

Log BAF (Arnot-Gobas upper trophic): 0.14 (BAF = 1.38 L/kg wet-wt)

Log Kow (experimental): not available from database

Log Kow used by BCF estimates: 0.87

Equation Used to Make BCF estimate: Log BCF = 0.50

Correction(s): Value

Correction Factors Not Used for Log Kow < 1

Estimated Log BCF = 0.500 (BCF = 3.162 L/kg wet-wt)

   

Bioaccumulation: terrestrial

 According to “ANNEX IX- STANDARD INFORMATION REQUIREMENTS FOR SUBSTANCES MANUFACTURED OR IMPORTED IN QUANTITIES OF 100 TONNES OR MORE , a bioaccumulation study need not be conducted if:

— the substance has a low potential for bioaccumulation (for instance a log Kow ≤ 3) and/or a low potential to cross biological membranes, or

— direct and indirect exposure of the aquatic compartment is unlikely.

The estimated Log BCF of Sodium ethyl xanthate is 0.5 (BCF = 3.162 L/kg wet-wt)

 

This substance has a limited potential to bioaccumulate (based on log Kow used :, Log Kow estimated : 0.87 , and predicted bioconcentration factors, log BCF = 0.5  (EPIWIN/BCF Program).

The estimated BCF of 3.162 L/kg wet-wt was measured by calculation from EPI SuiteTM v4.1 Program.

These values would suggest very low bioaccumulation potential.

This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency).

 

SMILES : S=C(S([Na]))OCC

CHEM  : Carbonodithioic acid, O-ethyl ester, sodium salt

MOL FOR: C3 H5 O1 S2 Na1

MOL WT : 144.18

--------------------------------- BCFBAF v3.01 --------------------------------

Summary Results:

 Log BCF (regression-based estimate): 0.50 (BCF = 3.16 L/kg wet-wt)

 Biotransformation Half-Life (days) : 0.0426 (normalized to 10 g fish)

 Log BAF (Arnot-Gobas upper trophic): 0.14 (BAF = 1.38 L/kg wet-wt)

 

Log Kow (experimental): not available from database

Log Kow used by BCF estimates: 0.87

 

Equation Used to Make BCF estimate: Log BCF = 0.50

 

     Correction(s):                   Value

      Correction Factors Not Used for Log Kow < 1

 

  Estimated Log BCF = 0.500 (BCF = 3.162 L/kg wet-wt)

 

===========================================================

Whole Body Primary Biotransformation Rate Estimate for Fish:

===========================================================

------+-----+--------------------------------------------+---------+---------

 TYPE | NUM | LOG BIOTRANSFORMATION FRAGMENT DESCRIPTION | COEFF | VALUE 

------+-----+--------------------------------------------+---------+---------

 Frag | 1 | Methyl [-CH3]                           | 0.2451 | 0.2451

 Frag | 1 | -CH2- [linear]                          | 0.0242 | 0.0242

 L Kow| * | Log Kow =  0.87 (KowWin estimate)       | 0.3073 | 0.2666

 MolWt| * | Molecular Weight Parameter               |        | -0.3697

 Const| * | Equation Constant                        |        | -1.5058

============+============================================+=========+=========

  RESULT  |       LOG Bio Half-Life (days)           |        | -1.3710

  RESULT  |           Bio Half-Life (days)           |        | 0.04256

  NOTE    | Bio Half-Life Normalized to 10 g fish at 15 deg C  |

============+============================================+=========

 

Biotransformation Rate Constant:

 kM (Rate Constant): 16.28 /day (10 gram fish)

 kM (Rate Constant): 9.157 /day (100 gram fish)

 kM (Rate Constant): 5.15 /day (1 kg fish)

 kM (Rate Constant): 2.896 /day (10 kg fish)

 

Arnot-Gobas BCF & BAF Methods (including biotransformation rate estimates):

  Estimated Log BCF (upper trophic) = 0.139 (BCF = 1.376 L/kg wet-wt)

  Estimated Log BAF (upper trophic) = 0.139 (BAF = 1.376 L/kg wet-wt)

  Estimated Log BCF (mid trophic)  = 0.121 (BCF = 1.322 L/kg wet-wt)

  Estimated Log BAF (mid trophic)  = 0.121 (BAF = 1.322 L/kg wet-wt)

  Estimated Log BCF (lower trophic) = 0.113 (BCF = 1.298 L/kg wet-wt)

  Estimated Log BAF (lower trophic) = 0.113 (BAF = 1.298 L/kg wet-wt)

 

Arnot-Gobas BCF & BAF Methods (assuming a biotransformation rate of zero):

  Estimated Log BCF (upper trophic) = 0.226 (BCF = 1.681 L/kg wet-wt)

  Estimated Log BAF (upper trophic) = 0.228 (BAF = 1.692 L/kg wet-wt)

 

 

Transport and distribution

Adsorption / desorption

 

 According to “ANNEX IX- STANDARD INFORMATION REQUIREMENTS FOR SUBSTANCES MANUFACTURED OR IMPORTED IN QUANTITIES OF 100 TONNES OR MORE , an adsorption study need not be conducted if:

— based on the physicochemical properties the substance can be expected to have a low potential for adsorption (e.g. the substance has a low octanol water partition coefficient), or

— the substance and its degradation products decompose rapidly.

 

The log of the adsorption coefficient (KOC) ofSodiumethyl xanthate was estimated to be log KOC = 0.602 which is equal to a KOC value of 4 using the KOCWIN v2.00 QSAR method. This value indicates that Reaction mass of SEX will be adsorbed by organic carbon in soil. Reaction mass of SEX can be classified to be of very high mobility in soil according these results and does not have a high potential for adsorption to soil

 

SEX and xanthates in generaladsorbs strongly to sulphide mineralsbut has less affinity for surfaces in general.

The KOC value of 4 also suggest this conclusion.

 

The estimated Soil Adsorption Coefficient was 4L/kg measured by calculation from EPI SuiteTM v4.1 Program. This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency

 

SMILES : S=C(S([Na]))OCC

CHEM  : Carbonodithioic acid, O-ethyl ester, sodium salt

MOL FOR: C3 H5 O1 S2 Na1

MOL WT : 144.18

 Koc Estimate from MCI:

        First Order Molecular Connectivity Index ........... : 2.770

        Non-Corrected Log Koc (0.5213 MCI + 0.60) .......... : 2.0438

        Fragment Correction(s):

                 1  Thiocarbonyl (C=S) .................. : -0.5701

                 1  Ether, aliphatic (-C-O-C-) .......... : -0.8716

        Corrected Log Koc .................................. : 0.6021

 

                        Estimated Koc: 4 L/kg  <===========

 

 Koc Estimate from Log Kow:

 -------------------------

        Log Kow (Kowwin estimate) ......................... : -2.24

        Non-Corrected Log Koc (0.55313 logKow + 0.9251) .... : -0.3139

        Fragment Correction(s):

                 1  Thiocarbonyl (C=S) .................. : 0.3004

                 1  Ether, aliphatic (-C-O-C-) .......... : -0.0906

        Corrected Log Koc .................................. : -0.1041

 

                        Estimated Koc: 0.7869 L/kg  <===========

 

 

 

Henry's Law constant

 

The estimated Henrys Law Constant (25 deg C) measured by calculation from EPI SuiteTM v4.1, HENRYWIN v3.20 Program was  7.494E-016 atm-m3/mole (7.593E-011 Pa-m3/mole) , which is almost zero.

This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency).

 

Distribution modelling.

 

 SEX has no affinity to be in air and sediment. The direct emissions to soil and surface water are significant, therefore SEX will be almost exclusively be found in soil and surface water.

 

Mackay fugacity modelling (level 3) indicates that, taking into account degradation and using inflow parameters which are consistent with the known production tonnage of this substance in, fugacity coefficient indicates that environmental concentrations in water are predicted to be 5.2e-019   (atm), in air (atm)   1.65e-020   and soil   8.69e-019    (atm) and sediment to be  1.5e-020  (atm).

These are negligible low levels. This can be considered a worse case prediction as it assumes all product is emitted with no emission control systems used.

 

 

Other distribution data

 

 These results suggest for SEX that direct and indirect exposure from distribution in media is unlikely.

Based on low vapor pressure and low estimated log Pow, expected to partition to water and soil. Not expected to partition to air, sediments or biota.

 

Therefore testing for distribution in media does not need to be performed.

 

The estimated STP Fugacity Model and Volatilization From Water were measured by calculation from EPI SuiteTM v4.1 Program. This is Exposure Assessment Tools and Models made from EPA (Environmental Protection Agency) .

 

                                                    Volatilization From Water

                                              =========================

 

 

Chemical Name: Carbonodithioic acid, O-ethyl ester, sodium salt

 

Molecular Weight   :     144.18 g/mole

Water Solubility   :       1E+006 ppm

Vapor Pressure     :      3.95E-009 mm Hg

Henry's Law Constant: 7.49E-016 atm-m3/mole (calculated from VP/WS)

 

                                            RIVER            

                                             ---------        ---------

Water Depth    (meters):      1                1         

Wind Velocity   (m/sec):      5                0.5       

Current Velocity (m/sec):     1                0.05      

 

     HALF-LIFE (hours) :  9.382E+011       1.023E+013

     HALF-LIFE (days ) :   3.909E+010       4.264E+011

     HALF-LIFE (years) :   1.07E+008        1.168E+009

 

 

STP Fugacity Model: Predicted Fate in a Wastewater Treatment Facility

===================================================================

  (using 10000 hr Bio P,A,S)

PROPERTIES OF: Carbonodithioic acid, O-ethyl ester, sodium salt

Molecular weight (g/mol)                              144.18

Aqueous solubility (mg/l)                             1E+006

Vapour pressure (Pa)                                   5.26623E-007

               (atm)                                             5.19737E-012

               (mm Hg)                                       3.95E-009

Henry 's law constant (Atm-m3/mol)             7.49354E-016

Air-water partition coefficient                       3.06464E-014

Octanol-water partition coefficient (Kow)    0.0057544

Log Kow                                               -2.24

Biomass to water partition coefficient                0.801151

Temperature [deg C]                                   25

Biodeg rate constants (h^-1),half life in biomass (h) and in 2000 mg/L MLSS (h):

         -Primary tank         0.04       16.00      10000.00

         -Aeration tank        0.04       16.00      10000.00

         -Settling tank          0.04       16.00      10000.00

 

                                     STP Overall Chemical Mass Balance:

                                 ---------------------------------

                                            g/h              mol/h         percent

 

Influent                            1.00E+001        6.9E-002       100.00

 

Primary sludge                2.50E-002        1.7E-004         0.25

Waste sludge                   1.50E-001        1.0E-003        1.50

Primary volatilization      4.08E-013        2.8E-015        0.00

Settling volatilization      1.11E-012        7.7E-015        0.00

Aeration off gas              2.74E-012        1.9E-014        0.00

 

Primary biodegradation    1.76E-003        1.2E-005       0.02

Settling biodegradation    5.27E-004        3.7E-006       0.01

Aeration biodegradation  6.93E-003        4.8E-005       0.07

 

Final water effluent            9.82E+000        6.8E-002       98.15

 

Total removal                    1.85E-001        1.3E-003        1.85

Total biodegradation          9.22E-003        6.4E-005        0.09