Barium sulfate

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

115 µg/L

Marine water

Hazard assessment conclusion:

no hazard identified

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

62.2 mg/L

Assessment factor:

10

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

600.4 mg/kg sediment dw

Assessment factor:

1

Sediment (marine water)

Hazard assessment conclusion:

insufficient hazard data available (further information necessary)

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

207.7 mg/kg soil dw

Assessment factor:

2

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Read across approach:

In the assessment of the environmental fate and behaviour of barium substances, a read-across approach is applied based on all information available for inorganic barium compounds. This is based on the common assumption that after emission of metal compounds into the environment, the moiety of toxicological concern is the potentially bioavailable metal ion (i.e., Ba2+). The dissolution of barium substances in the environment and corresponding dissolved Ba levels are controlled by the solubility of barite (BaSO₄) and witherite (BaCO₃), two naturally occurring barium minerals (Ball and Nordstrom 1991; Menzie et al, 2008), and the concentration of dissolved Ba cations in freshwater is rather low. However, in the dissolved state, the divalent barium cation, is the predominant form in soil, sediments and water. The solubility of barium compounds increases as solution pH decreases (US EPA, 1985a). Nevertheless, the speciation of barium in the environment is considered to be rather simple (USEPA 2005):

-         Barium cations are not readily oxidized or reduced

-         Barium cations do not bind strongly to most inorganic ligands or organic matter

 

Barium  in soils  is not  expected  to  be  very mobile  because of the formation  of water-insoluble salts (sulphate and carbonate) and its inability to form soluble complexes with humic and fulvic materials.  Under acid conditions, however, some of the  water-insoluble  barium compounds  may become soluble and move into ground water (US EPA, 1984).

 

In sum, transport, fate, and toxicity of barium in the environment are largely controlled by the solubility of barium minerals. The barium cation is the moiety of toxicological concern, and thus the hazard assessment is based on Ba2+.

 

US EPA (1985a) Health advisory — barium. Washington, DC, US Environmental Protection Agency, Office of Drinking Water.

 

US EPA (1984) Health effects assessment for barium,Cincinnati, Ohio, US Environmental Protection Agency, Office of Health and Environmental

Assessment, Environmental Criteria and Assessment Office (Prepared for the Office of Emergency and Remedial Responsible, Washington, DC) (EPA 540/1-86-021).

PNEC marine water:

A relevant PNEC for the marine environment cannot be determined, for the following reasons:

(i) Barium levels in sea water range from 2 to 63 μg/L with a mean concentration of about 13 μg/L (Bowen 1979).

(ii) Applying ECHA-guidance, the derived marine PNEC of 11.5μg/L for barium (PNEC freshwater = 1.15 mg Ba/L and an AF of 100) would thus be within the range of typical barium seawater levels.

(iii) Seawater contains about 2700 mg/L sulfate (Hitchcock, 1975 cited in WHO, 2004).

(iv) Barium transported into marine systems combines with sulfate ions present in salt water to form barium sulfate.

(v) Barium in marine environments is in a steady state; the amount entering is balanced by the amount falling to the bottom as barium sulfate (barite) particles to form a permanent part of the marine sediment (Wolgemuth & Brocker, 1970). Thus, dissolved barium concentrations are controlled by the solubility of barium sulfate. The solubility product (K_sp) of barium sulfate is 1.08E^-10(CRC Handbook, 2008), resulting in maximum dissolved Ba levels of approximately 1.4 mg/L.

(vi) In sum, due to high sulfate levels in the marine environment and a low solubility of barium sulfate, dissolved barium levels will remain constant in marine waters, regardless of the amount of barium introduced to the system.

 

References:

Bowen HMJ (1979) Environmental Chemistry of the Elements. Academic Press, London, 333 pp.

Lide, D.R. (2008) CRC Handbook of chemistry and physics. 88^thedition.

Hitchcock DR (1975) Biogenic contributions to atmospheric sulphate levels. In: Proceedings of the 2nd National Conference on Complete Water Re-use. Chicago, IL, American Institute of Chemical Engineers.

WHO (1990) Barium. Environmental Health Criteria 107. International Programme on Chemical Safety.

WHO (2004) Sulfate in Drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality. WHO/SDE/WSH/03.04/114.

Wolgemuth K & Broecker WS (1970) Barium in sea water. Earth planet. Sci. Lett., 8: 372-378.

PNEC sediment:

The PNEC_sedimentcan be derived from the PNEC_aquaticusing the equilibrium partitioning method (EPM).

A distribution/partition coefficient (K_D) between water and suspended matter for barium has been determined (see chapter 4). This resulted in a typical K_D,suspof 5,217 L/kg (logK_D: 3.72). In a first step the units have to be converted from L/kg to m³/m³using the formula below.

K_D,susp(m³/m³) = 0.9 + [0.1 x (K_D,susp(L/kg) x 2,500) / 1,000 ]

This results in a K_D,suspof 1,305..2 m³/m³. This value can be entered in the equation below to calculate the PNEC_sediment:

PNEC_sediment= (K_D,susp/ RHO_susp) x PNEC_aquaticx 1,000

with the PNEC_aquaticexpressed as mg/L, RHO_susprepresenting the bulk density of wet sediment (1,150 kg/m3) anda K_D,suspof 1,305.2 m³/m³, a PNEC_sedimentthat is expressed as mg/kg wet weight can be derived. This value can be converted to a dry weight-based PNEC, using a conversion factor of 4.6 kg wet weight/ kg dry weight.

This results in aPNEC_sedimentof 600.4 mg Ba/kg dry sediment

 

PNEC soil:

 

Derivation of a PNEC for the terrestrial compartment according to the assessment factor method resulted in a PNEC well below typical background levels for the majority of EU-countries. Therefore a more relevant PNEC was derived based on reported baseline levels of Ba in EU top soil samples. The outlier cut-off level for Ba baseline levels (i.e., 415.7 µg/L) was used as a starting point and an additional AF of 2 was applied on this value. The value of 207.7 mg Ba/kg dry wt is considered as a reliable, PNEC for the terrestrial compartment. For more information please refer to the CSR.

 

 

PNEC for sewage treatment plant:

In general, an AF of 10 is to be applied to the NOEC/EC₁₀of a sludge respiration test, reflecting the lower sensitivity of this endpoint as compared to nitrification, as well as the short duration of the test. The corresponding AF is 100 when based on the EC₅₀. The PNEC_{micro-organism}is set equal to a NOEC (AF = 1) for a test performed with specific bacterial populations such as nitrifying bacteria,P. putida, ciliated protozoa, the Shk1 Assay. An EC₅₀from this test is divided by an AF of 10 to derive the_{PNECmicro-organism}. No AF is needed to derive a PNEC_{micro-organism}based on good quality field data.

The lowest reliable observed NOEC/EC₁₀-value for respiration (inhibition of respiration after a 3h incubation period) using activated sludge was ≥943.1 mg BaCl2/L (corresponding to 622 mg Ba/L). Based on the guidance given in the RIP3.2 (ECHA, 2008) and the TGD (2003), an assessment factor of 10 should be used on this value, as respiration is the endpoint.

Application of an assessment factor of 10 on this value of 622 mg Ba/L, results in a PNEC_{micro-organism}of 62.2 mg Ba/L.

Conclusion on classification

Using the currently available acute and chronic toxicity reference values, the environmental classification of barium sulfate is presented here.

In a first step, the acute and chronic reference value (based on total Ba in the solution) is transformed to a value expressed as Ba-sulfate. Transformation is achieved by dividing the acute and chronic reference values by the fraction of Ba (molecular weight-based) in this substance, i.e., 58.8%.

Short-term toxicity EC/LC50 values of barium available for 3 trophic levels are situated between > 1.15 mg Ba/L and 14.5 mg Ba/L, corresponding to > 1.96 mg/L and 24.7 mg/L barium sulfate. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (a), classification for acute aquatic hazard is not required for barium sulfate as all EC50/LC50 values are above the classification criteria of 1 mg/L.

Long-term toxicity data are available for three trophic levels and range from ≥ 1.15 mg Ba/L to 2.9 mg Ba/L, corresponding to ≥ 1.96 mg/L and 4.93 mg/L barium sulfate. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (b) (i), classification for chronic aquatic hazard is not required for barium sulfate as all chronic EC10/NOEC values are above the classification criteria of 1 mg/L.