Dichlobenil

Endpoint summary

Additional information

Fate and behaviour in soil

In laboratory studies the half-life of the test material under aerobic circumstances has been investigated. The DegT₅₀ values, excluding volatilisation, from these studies have been normalised to 20 °C and common moisture content resulting in a normalised geometrical mean DegT₅₀ of 24.15 days (range 21.98 - 26.26 days). Under anaerobic conditions the test material was not metabolised (half-life was 1040 days or 2.85 years) and therefore other factors such as volatilisation will dominate in the loss of test material in an anaerobic environment. The degradation rate of the test material in soil under laboratory conditions is moderate. Accumulation of the test material residues in soil over successive years is, however, considered not to be significant. In particular, because the field dissipation rates (taking into account also other routes of dissipation, like volatilisation of the test material from the soil surface) are considerably lower. The dissipation of the test material was studied after application at a rate of 120 kg/ha in Germany on four different soils. The mean DT₅₀ for the test material was calculated to be 35 days and the mean DT₉₀ was 202 days. In laboratory studies it was determined that degradation of the test material in soil under aerobic conditions leads to the formation of one major metabolite ≥10% of applied): 2,6-dichlorobenzamide.

Fate and behaviour in water

Groundwater: On the basis of the Koc values (average = 237) it can be concluded that the test material has a low mobility in soil. In the aged leaching study it was shown that the test material does not penetrate further than 15 cm in a sandy loam soil, whereas only 3 % of the aged residue had leached through the column.

Surface water: Based on the application method and the nature of the granular formulation, spray drift is not a relevant route of entry of the test material to surface water. Surface water may be exposed via run-off or drainage. In the water/sediment study it was shown that the test material in the water phase is removed through volatilisation (major process) and degradation. The dissipation half-life of the test material in the aqueous phase ranges from 10.1-10.9 days, based on first order kinetics and 3.5- 6.3 days, based on the hockystick model.

Fate and behaviour in air The test material has a moderate vapour pressure (1.4 x 10^-1 Pa at 25 °C). The gas-phase oxidation rate of the test material in the troposphere was predicted to be 0.1704 x 10 ^-12 cubic cm/molecule-sec. Based on a hydroxyl radical concentration of 1.56 x 10⁶ molecules/cm³ (12-hour day), a half live of 62.78 days was calculated. The test material will, however, not persist in the atmosphere. It has been demonstrated that it can degrade rapidly in air under the influence of light to form a number of volatile photo-degradation products. The calculated half-time of [¹⁴C]-dichlobenil in air is 2.8 days in the SUNTEST, which equals 1.4 days of natural sunlight at 50° Northern latitude as specified by the US-EPA. The quantum yield was 0.06 mole/Einstein. Overall, the test material is unlikely to be subject to long range transport, and with a logK_ow of 2.7 will not bioaccumulate either.