Ozone

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.008 µg/L

Assessment factor:

1 000

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.08 µg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.001 µg/L

Assessment factor:

10 000

Extrapolation method:

assessment factor

PNEC marine water (intermittent releases):

0.008 µg/L

STP

Hazard assessment conclusion:

no emission to STP expected

Sediment (freshwater)

Hazard assessment conclusion:

no exposure of sediment expected

Sediment (marine water)

Hazard assessment conclusion:

no exposure of sediment expected

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no exposure of soil expected

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Ozone, being a strong oxidiser, is toxic to most living organisms, in varying degrees, as shown in the toxicity section of this dossier. Demonstrated by the efficacy studies, ozone is generally much more reactive and hence toxic in aqueous solution than in dry air.

Various existing studies on aquatic organisms clearly demonstrate that ozone dissolved in water is highly toxic to aquatic organisms such as fish and invertebrates. These studies result in the classifications "Aquatic Acute 1" and "Aquatic Chronic 1".

A PNECwater of 0.008 µg/L was derived for ozone (applying an AF of 1000).

Significant exposure of sediment or soil is considered unlikely, and tests on sediment dwelling organisms and soil microorganisms are considered not necessary, since ozone has a very short half-life under real world conditions, often less than a minute, and since the emission of ozone to water is very low. As Ozone is a gas and will move to the atmosphere after being released in the environment an exposure of soil and/or sediment organisms is considered to be negligible. Moreover, ozone is a reactive substance which will, as soon as it comes into contact with soil, react immediately with soil components such as organic material and metal ions.

In seawater, typically containing high bromide ion concentrations, ozone will react very quickly with e.g. bromide, resulting in formation of "active bromine" which is measured in marine studies as TRO (total residual oxidants) or OPO (ozone produced oxidants). These oxidants are toxic to fish and invertebrates. In applications of ozone in e.g. water treatment of marine aquaria, continuous measurement of the oxidation reduction potential (ORP) is therefore a good measure of the relative oxidizing power of the water, and it has to be low enough before aquatic organisms come into contact with the treated water.

The studies on birds showed toxic effects on poultry but did not allow deduction of a no-effect level. For birds and arthropods, however, no exposure to ozone is expected, because the amounts of ozone released to the atmosphere are negligible when compared to the level of ozone already present in ambient air. During normal use of ozone in the envisaged applications, no additional exposure of birds to ozone is therefore expected.

Since ozone is highly reactive, bioconcentration or bioaccumulation is neither expected in aquatic nor in terrestrial organisms.

Conclusion on classification

Aquatic Acute 1: All LC50 values for fish and invertebrates were substantially lower than 1 mg/l, the upper limit for classification of a substance for acute aquatic toxicity in category 1.

Aquatic Chronic 1: Based on the data of Wedemeyer et al (1979) it is concluded that it is likely that the NOEC_chronic for ozone in fish is ca. 2 µg/L. Consequently ozone, being a substance which is rapidly degraded, should be classified for chronic aquatic toxicity category 1.