Ammonium perchlorate

Biodegradation in water and sediment: simulation tests

Description of key information

Biodegradation in sediment and water and identification of degradation products are not required according to Annex IX because of a combination of three aspects: for sediment, no adsorption to sediment is expected + degradation is unlikely and highly dependent on media, bacterial and nitrate contents, so that as a worst-case it seems more relevant to consider an absence of degradation; + investigation of degradation is not useful for PBT/vPvB assessment as there is no relevant bioaccumulation in fish.

Additional information

Water:

Degradation in surface water and identification of degradation products were considered not to be useful for risk assessment because the substance is inorganic and does not bioaccumulate so that it is neither PBT nor vPvB. Furthermore, perchlorate is known for being stable in various media, and its degradation could be dependent on various media characteristics (see sediment, below).

Sediment:

A literature study investigated the intrinsic perchlorate degradation kinetics of sediments and soils from multiple sites in microcosm studies, including the influence of varying nitrate concentration (from 1 to 22.8 ppm) and up to 300 ppm sulfate. The first-order degradation rates and lag times of both perchlorate and nitrate degradation were site-specific and dependent on environmental conditions such as organic substrate availability, nitrate, initial perchlorate concentration, and prior perchlorate exposure. At an initial perchlorate concentration of 5 ppm, perchlorate degradation rates ranged from 0.13 to 0.46 day^-', and lag times of perchlorate degradation ranged from 0 to 60.0 days: while nitrate degradation occurred at rates ranging from 0.03 to 1.42 day- 1, with tag times ranging from 0 to 29.7 days. Under the same treatment conditions, nitrate degradation rates were relatively higher than that of perchlorate. Perchlorate degradation rates remained constant at both lower (0.5 ppm) and higher (5 ppm) perchlorate concentrations. Generally, perchlorate rates were affected by the availability of organic substrate, which was represented here by total volatile solids of sediments and soils, and not by nitrates. Nitrate did increase the lag time of perchlorate degradation, which may account for the persistence of perchlorate in the environment, especially when perchlorate is typically ppb levels in the environment compared to ppm levels of nitrates. This study showed rapid intrinsic perchloratedegradation in sediments and soils of contaminated sites, and highlighted the potential for natural attenuation of perchlorate in the environment.

In another study, the transformation of perchlorate was investigated in river sediment during laboratory batch and column studies to determine if reduction of perchlorate is a viable pathway in natural sediment without previous exposure to perchlorate. Perchlorate at an initial concentration of 10 µM was reduced quantitatively to chloride in 3 days after a lag phase of 2 days in sediment slurries amended with lactate. Raising the initial concentration of perchlorate to 1,000 increased the tag phase to 20 d before reduction occurred. At perchlorate concentrations greater than 1,000 µM, the reduction of perchlorate was not observed within 40d. The authors speculate that the high concentration of perchlorate specifically was problematic to the microbes mediating the reduction of perchlorate. High levels of nitrate inhibited the reduction of perchlorate as well. In sediment slurries amended with 870 µM sodium nitrate, the reduction of perchlorate at an initial concentration of 100 µM did flot occur before day 15 of the experiment, but complete removal of nitrate had occurred by day four. Sediment column studies further demonstrated the dependence of perchlorate reduction on endogenous nitrate levels.

The following information is taken into account for any hazard / risk / persistency assessment:

Biodegradation in sediment and identification of degradation products are not required according to Annex IX because of a combination of three aspects: no adsorption to sediment is expected + degradation is unlikely and highly dependent on media, bacterial and nitrate contents, so that as a worst-case it seems more relevant to consider an absence of degradation; + investigation of degradation is not useful for PBT/vPvB assessment as there is no relevant bioaccumulation in fish.