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Environmental fate & pathways

Endpoint summary

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Environmental fate and pathways

 

Environmental Fate/Exposure Summary: 

Environmental exposure

 

S-allyl O-pentyl dithiocarbonate is used in the mining industry as flotation agents as a fine collector for metallic copper, molybdenite, and sulfidized base metal oxides. 
The amount of S-allyl O-pentyl dithiocarbonate used is very small relative to the quantity of ore treated, being approximately 2 to 50 g/tonne of ore.

 

The flotation process is fully automated. The process takes place in open tanks. However, the concentration of S-allyl O-pentyl dithiocarbonate in the flotation tank is low and, therefore, the release of Carbon monoxide; carbon dioxide; oxides of nitrogen; oxides of sulphur (includes sulphur di and tri oxides) would be expected to be low.

Air monitoring data, although limited and of poor quality, indicate that the atmospheric levels of carbon dioxide; oxides are below 10 ppm in the flotation areas. The risk to workers during the flotation process is considered to be low.

                                                                                                    

 

Environmental fate

 

S-allyl O-pentyl dithiocarbonate was hydrolytically stable (half life > 1 year) specified by the OECD Guidelines. This substance has a limited potential to bioaccumulate (based on log Kow used by BCF estimates: 73.06 and predicted bioconcentration factors, log BCF = 1.864 (EPIWIN/BCF Program).

 

S-allyl O-pentyl dithiocarbonate is not expected to contaminate the environment where ore tailings are confined to well constructed 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.

 

Critical Health Effects

The critical health effects for risk characterisation include, a systemic acute effect (acute toxicity from oral exposure) and a local effect (skin irritation and eye irritation).

Public Risk Characterisation

Given that there are no consumer uses identified for the chemical, it is unlikely that the public will be exposed. Hence, the public risk from this chemical is not considered to be unreasonable.

Occupational Risk Characterisation

During product formulation, oral and dermal exposure might occur, particularly where manual or open processes are used. These could include transfer and blending activities, quality control analysis, and cleaning and maintaining equipment. Worker exposure to the chemical at lower concentrations could also occur while using formulated products containing the chemical. The level and route of exposure will vary depending on the method of application and work practices employed.

Given the critical systemic long-term, systemic acute and local health effects, the chemical could pose an unreasonable risk to workers unless adequate control measures to minimise oral and dermal exposure are implemented. The chemical should be appropriately classified and labelled to ensure that a person conducting a business or undertaking (PCBU) at a workplace (such as an employer) has adequate information to determine the appropriate controls.

 

 

 Stability

 

Phototransformation in air

 

If released to air, a vapor pressure of  0.00316mm Hg at 25 deg C (0.00316mm Hg is equivalent to vapour pressure of 0.421Pa ) indicates S-allyl O-pentyl dithiocarbonate will exist solely as a vapor in the atmosphere. Vapor-phase S-allyl O-pentyl dithiocarbonate 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 0.218 days, calculated from its rate constant of 49.0430 E-12 cm3/molecule-sec at 25 deg. S-allyl O-pentyl dithiocarbonate do not contain chromophores that absorb at wavelengths >290 nm and therefore S-allyl O-pentyl dithiocarbonate is not expected to be susceptible to direct photolysis by sunlight.

 Using the AOPWIN QSAR model, the photochemical degradation rate of S-allyl O-pentyl dithiocarbonate in the atmosphere is 49.0430E-12cm3/molecule-sec, with a resultant predicted half live of 2.617Hrs(0.218 Days (12-hr day; 1.5E6 OH/cm3))

 OVERALL OH Rate Constant = 49.0430 E-12 cm3/molecule-sec

  HALF-LIFE =    0.218 Days (12-hr day; 1.5E6 OH/cm3)

  HALF-LIFE =    2.617 Hrs

 

Phototransformation in water

It is not applicable for a compound wich is  slightly soluble or almost insoluble

 Phototransformation in soil

If released to soil, S-allyl O-pentyl dithiocarbonate  is expected to have  high mobility based upon an estimated Koc of 153.4 . 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).

 The hydrolysis of the substance was less than 10% over the 5 days, so a definitive test was not performed. Based on these results, S-allyl O-pentyl dithiocarbonate  was hydrolytically stable (half life > 1 year) specified by the OECD Guidelines .

 

  

    Biodegradation

Biodegradation in water: screening tests

 

Based on the results, S-allyl O-pentyl dithiocarbonate is readily biodegradable: 73.74 % was degraded in 8 days (at initial pH 7.4 and 25 oC). The calculated half-life (t1/2) was 4.6 d. Xanthates with branched alkyl chains can be expected to have slightly lower rate of biodegradation. The results show the rapid biodegradability of the initial substance, but suggest that the main degradation products which cannot be further mineralised by microbes are carbon disulfide, monothiocarbonate and dixanthogen, which accumulated in the test solution. Despite of that, no significant toxic or inhibitory effects on micro-organisms were observed at an initial test concentration of 30 mg/L.

 

  

Biodegradation in water and sediment: simulation tests

 

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. Pentan-1-ol/Amyl alcohol, Carbon disulphide and Allyl Chloride are both reagents used in the manufacture of S-allyl O-pentyl dithiocarbonate.Therefore, the Biodegradation in water of Pentan-1-ol/Amyl alcohol, Carbon disulphide and Allyl Chloride need to be considered in the assessment of S-allyl O-pentyl dithiocarbonate. The results suggest that Pentan-1-ol/Amyl alcohol, Carbon disulphide and Allyl Chloride are readily biodegradable and S-allyl O-pentyl dithiocarbonate will be readily biodegradable and it is not expected to persist in the environment. As S-allyl O-pentyl dithiocarbonate 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, S-allyl O-pentyl dithiocarbonate is expected to have very high mobility based upon an estimated Koc of 153.4. 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

 

QSAR estimation using the BCFBAF v3.01 of the EPISUITE 4.1 indicate that the BCF of S-allyl O-pentyl dithiocarbonate  is 73.06  L/kgwwt. This is well below the threshold for Bioaccumulation (B) for the PBT determination.

 

 

  

Bioaccumulation: terrestrial

 This substance has a limited potential to bioaccumulate (based on log Kow used by BCF estimates: 3.33,The estimated Log BCF of S-allyl O-pentyl dithiocarbonate is 1.864 (BCF = 73.06 L/kg wet-wt) 

 

   

Transport and distribution

Adsorption / desorption

 

The log of the adsorption coefficient (KOC) of S-allyl O-pentyl dithiocarbonate was estimated to be log KOC = 2.1858 which is equal to a KOC value of 153.4 using the KOCWIN v2.00 QSARmethod. This value indicates that S-allyl O-pentyl dithiocarbonate will be adsorbed by organic carbon in soil.

S-allyl O-pentyl dithiocarbonate 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. S-allyl O-pentyl dithiocarbonate adsorbs strongly to sulphide minerals but has less affinity for surfaces in general. The KOC value of 153.4 also suggest this conclusion.

 

 

 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 1.425E-005 atm-m3/mole  (1.444E+000 Pa-m3/mole).

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

 

Distribution modelling.

 

S-allyl O-pentyl dithiocarbonate has no affinity to be in air and sediment. The direct emissions to soil and surface water are significant, therefore S-allyl O-pentyl dithiocarbonate  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  1.98e-010 (atm), in air (atm)   7.66e-012 and soil   1.54e-009 (atm) and sediment to be   1.66e-010 (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 S-allyl O-pentyl dithiocarbonate 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: Carbonic acid, dithio-, S-allyl O-pentyl ester

 

Molecular Weight   : 204.35 g/mole

Water Solubility   : -----

Vapor Pressure     : -----

Henry's Law Constant: 2.4E-005 atm-m3/mole (estimated by Bond SAR Method)

 

                            RIVER            LAKE

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

Water Depth    (meters):  1                1         

Wind Velocity   (m/sec):  5                0.5       

Current Velocity (m/sec):  1                0.05      

 

     HALF-LIFE (hours) :  36.33            516.2     

     HALF-LIFE (days ) :  1.514            21.51     

 

 

STP Fugacity Model: Predicted Fate in a Wastewater Treatment Facility

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

  (using 10000 hr Bio P,A,S)

PROPERTIES OF: Carbonic acid, dithio-, S-allyl O-pentyl ester

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

Molecular weight (g/mol)                              204.35

Aqueous solubility (mg/l)                             0

Vapour pressure (Pa)                                  0

               (atm)                                 0

               (mm Hg)                               0

Henry 's law constant (Atm-m3/mol)                    2.4E-005

Air-water partition coefficient                       0.000981529

Octanol-water partition coefficient (Kow)             2137.96

Log Kow                                               3.33

Biomass to water partition coefficient                428.392

Temperature [deg C]                                   25

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

         -Primary tank       0.00     4614.35      10000.00

         -Aeration tank      0.00     4614.35      10000.00

         -Settling tank      0.00     4614.35      10000.00

 

 STP Overall Chemical Mass Balance:

 ---------------------------------

                            g/h              mol/h         percent

 

Influent                   1.00E+001        4.9E-002       100.00

 

Primary sludge             4.95E-001        2.4E-003        4.95

Waste sludge               4.54E-001        2.2E-003        4.54

Primary volatilization     1.10E-002        5.4E-005        0.11

Settling volatilization    2.93E-002        1.4E-004        0.29

Aeration off gas           7.94E-002        3.9E-004        0.79

 

Primary biodegradation     3.00E-003        1.5E-005        0.03

Settling biodegradation    8.81E-004        4.3E-006        0.01

Aeration biodegradation    1.16E-002        5.7E-005        0.12

 

Final water effluent       8.92E+000        4.4E-002       89.16

 

Total removal              1.08E+000        5.3E-003       10.84

Total biodegradation       1.55E-002        7.6E-005        0.15

 

 

 

 

 

 

 

 

 

 

 

 

 

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