APPENDIX 4
Fact sheets on chemical compounds

Crocidolite (asbestos)

Common formulation

Na₂₀Fe₂O₃. 3FeO. *SiO₂. H₂O

CAS registry number

12001-28-4

Use

Crocidolite — together with anthophyllite and actinolite — belongs to the group of asbestos. It is used as an inert filler medium, a reinforcing material in vinyl and asphalt flooring products (former use), fire- and rot-resistant material in felts, raw material for asbestos-based paper, a component of industrial talcs, etc.

CROCIDOLITE IN THE ENVIRONMENT

• Mobility

It appears that asbestos does not have an adsorptive affinity for solids.

• Degradation

Asbestos is considered to be non-biodegradable by aquatic organisms. As a mineral it is not affected by photolytic processes.

• Degradation products

No data available.

• Volatilization/evaporation

Not volatile.

• Bioaccumulation

No evidence has been found regarding the bioaccumulation of asbestos in aquatic organisms.

• Phytotoxicity

Not applicable.

PROPERTIES

Asbestos forms a blue fibre. It does not burn or rot and possesses extremely high tensile strength as well as resistance to acids, alkalis and heat.

TABLE A

Parameters

1,2-dibromoethane

Common formulation

C₂H₄Br₂

CAS registry number

106-93-4

Use

Formerly used as an insecticide, fumigant and nematicide.

1,2-DIBROMOETHANE IN THE ENVIRONMENT

• Mobility

1,2-dibromoethane exhibits moderate adsorption to soil.

• Degradation

1,2-dibromoethane biodegrades fairly readily in the environment. Its half-life can be as short as several days in surface soils and as long as many months in aquifer materials. Persistence can vary greatly from soil to soil. An experimental half-life ranging from 1.5 to 18 weeks has been determined. The long persistence was observed in one field where dibromoethane was detected 19 years after the last known application. This long persistence was a result of its entrapment in intraparticle micropores of the soil. In groundwaters 1,2-dibromoethane can be degraded by biodegradation and hydrolysis. Uncatalysed hydrolysis is slow (half-life six years) but hydrolysis catalysed by the presence of various natural substances may be competitive with biodegradation (half-life one to two months). 1,2-dibromoethane is removed from water primarily by evaporation.

• Degradation products

The major degradation product of 1,2-dibromoethane is 2-bromoethanol.

• Volatilization/evaporation

Based on its vapour pressure, 1,2-dibromoethane is thought to volatilize. The volatilization half-life in rivers and lakes is about 1 day and 5 days, respectively. In the atmosphere, 1,2-dibromoethane degrades photochemically (half-life 32 days).

• Bioaccumulation

Based on the low log K_ow (of 1.96) 1,2-dibromoethane is thought not to accumulate in aquatic organisms.

• Phytotoxicity

Not applicable.

PROPERTIES

1,2-dibromoethane is a colourless liquid or solid.

TABLE B

Parameters

Polybrominated biphenyls (PBBs)

Common formulation

C₁₂H₄Br₆

CAS registry number

67774-32-7

Use

Polybrominated biphenyls are manufactured substances used as a pesticide to control a variety of harmful pests that attack many field crops and vegetables.

POLYBROMINATED BIPHENYLS IN THE ENVIRONMENT

• Mobility

PBBs bind moderately to soil and do not leach out easily.

• Degradation

Natural chemical reactions and bacteria may remove PBBs from soil and water. PBBs take about seven days to break down in water. In soil, they take about 3.5 to 290 days for half of them to break down, depending on soil type, moisture, and temperature.

• Degradation products

No data currently available.

• Volatilization/evaporation

No data currently available.

• Bioaccumulation

PBBs will accumulate in aquatic organisms.

• Phytotoxicity

No data currently available.

PROPERTIES

Polybrominated biphenyl is a colourless oil.

TABLE C

Parameters

Polychlorinated biphenyls (PCBs)

CAS registry number

1336-36-3

Use

Formerly as hydraulic fluids, plasticiser in synthetic resins, adhesives, heat transfer systems, wax extenders, pesticide extenders, inks, etc.

PCBS IN THE ENVIRONMENT

• Mobility

If released into soil, PCBs experience tight adsorption with adsorption generally increasing with the degree of chlorination of the PCB. They generally do not leach significantly in aqueous soil systems; the higher chlorinated congeners have a lower tendency to leach than the lower chlorinated congeners. In the presence of organic solvents, PCBs may leach quite rapidly through soil.

• Degradation

PCBs are mixtures of different congeners of chlorobiphenyl, and the relative importance of the environmental fate mechanisms generally depends on the degree of chlorination. In general, the persistence of PCBs increases with an increase in the degree of chlorination. Mono-, di- and trichlorinated biphenyls biodegrade relatively rapidly, tetrachlorinated biphenyls biodegrade slowly, and higher chlorinated biphenyls are resistant to biodegradation. Although the biodegradation of higher chlorinated congeners may occur very slowly on an environmental basis, no other degradation mechanisms have been shown to be important in natural water and soil systems; therefore, biodegradation may be the ultimate degradation process in water and soil. When released into water, adsorption to sediment and suspended matter is an important fate process; PCB concentrations in sediment and suspended matter have been shown to be greater than in the associated water column. Although adsorption can immobilize PCBs (especially the higher chlorinated congeners) for relatively long periods of time, eventual re-solution into the water column has been shown to occur. The PCB composition in the water is enriched by the lower chlorinated PCBs because of their greater water solubility, and the least water soluble PCBs (highest chlorine content) remain adsorbed. In the absence of adsorption, PCBs volatilize from water relatively rapidly. However, strong PCB adsorption to sediment significantly competes with volatilization, with the higher chlorinated PCBs having a longer half-life than the lower chlorinated PCBs. Although the resulting volatilization rate may be low, the total loss by volatilization over time may be significant because of the persistence and stability of the PCBs.

• Degradation products

Polychlorinated biphenyls degrade into less-chlorinated PCBs.

• Volatilization/evaporation

Vapour loss of PCBs from soil surfaces appears to be an important fate mechanism, with the rate of volatilization decreasing with increasing chlorination. Although the volatilization rate may be low, the total loss by volatilization over time may be significant because of the persistence and stability of PCBs. Enrichment of the low-chlorine PCBs occurs in the vapour phase relative to the original Aroclor; the residue is enriched in the PCBs containing high chlorine content. The dominant atmospheric transformation process is probably the vapourphase reaction with hydroxyl radicals, which have estimated half-lives ranging from 12.9 days for monochlorobiphenyl to 1.31 years for heptachlorobiphenyl.

• Bioaccumulation

PCBs have been shown to bioconcentrate significantly in aquatic organisms. Average log BCFs of 3.26 to 5.27, reported for various congeners in aquatic organisms, show increasing accumulation with the more highly chlorinated congeners.

• Phytotoxicity

Not applicable.

TABLE D

Parameters

Tris (2, 3-dibromo-1-propyl) phosphate

Common formulation

C₉H₁₅Br₆O₄P

CAS registry number

126-72-7

Use

Recommended for use in phenolic resins, paints, paper coatings and rubber (former uses). Rigid foams containing tris (2,3-dibromopropyl) phosphate are used in insulation, water flotation devices and furniture.

TRIS (2, 3-DIBROMO-1-PROPYL) PHOSPHATE IN THE ENVIRONMENT

• Mobility

A log K_oc value of 3.2 indicates that tris (2,3-dibromo-1-propyl) phosphate is immobilized in soil due to strong adsorption.

• Degradation

The biodegradation of tris occurs in activated sludge. A biodegradation half-life of 19.7 hours was obtained for tris in a laboratory-activated sludge system. No data are available regarding biodegradation in natural soils or waters. The hydrolysis and photolysis of tris is thought to be not important.

• Degradation products

No data available.

• Volatilization/evaporation

No data concerning the volatilization from water or soil are available.

• Bioaccumulation

Based on octanol-water partition coefficient, tris is thought to accumulate moderately in aquatic organisms.

• Phytotoxicity

Not applicable.

PROPERTIES

Tris (2,3-dibromopropyl) phosphate is a yellow liquid. It does not hydrolyse and is stable up to about 200°C.

TABLE E

Parameters