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Environmental fate & pathways

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STABILITY

Sodium phosphite is considered a very stable substance. It is not subject to biodegradation, even if some literature demonstrates that some microorganisms are able to transform phosphite ion in phosphate: Foster and Winans (1977) and Foster et al. (1978) isolated from Cape Canaveral soil microorganisms (identified as Bacillus spp., a ubiquitous spore former) that are capable of utilizing phosphite as their phosphorus source, under anaerobic conditions. Quantitative essays of labelled phosphorous demonstrated the incorporation of phosphorus from phosphite into the cell as organic phosphate. It was assumed that more microorganisms with such ability exist. Foster et al. (1978) further investigated the anaerobic phosphite utilisation by Bacillus spp., and found that it is a facultative anaerobe, which uses phosphite in preference to hypophosphite. It should be noted that when phosphate was present in the medium, no metabolism of phosphite occurred.

Nevertheless other sources related to PPP reports a DT50 soil of 157 days.

The substance could be considered persistent (DT50>120) but not very persistent (DT50>180). Further tests are in course for verification.

Reference:

T L Foster, L Winans, Jr, andS J Helms, Anaerobic utilization of phosphite and hypophosphite by Bacillus sp.,Appl Environ Microbiol.1978 May;35(5): 937–944.

- Hydrolysis:In water the substance is completely dissociated to phophite ions and sodium. The phosphite ion and the sodium cation are considered to be stable in water solution. The product is in fact produced in water solution and stability of the samples is declared of some years.

- Phototransformation in water an soil: no data, but phosphorous acid is not expecting to absorb light at more than 290nm, therefore photodegradation is not expected.

Due to its physico-chemical properties, potassium phosphite is not distributed or transported to the atmosphere. Thus, the environmental risk assessment will not focus on this compartment. The substance is an inorganic salt, very soluble and the main interested compartment is water