Calcium hydrogen phosphonate

Toxicity to soil microorganisms

Administrative data

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

September 2004 - December 2005

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Published paper on a field study. Many details included.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2007

Materials and methods

Principles of method if other than guideline:

Field study measuring soil microbial enzyme activities and soil mesofauna feeding activity

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Potassium phosphite, aqueous KH2PO3 solution

IUPAC Name:

Potassium phosphite, aqueous KH2PO3 solution

Test material form:

other: aqueous solution

Details on test material:

KH2PO3 solution delivered by KEMIRA GrowHow GmbH Hanover

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

Monthly samples were taken in September and October 2994 and from April 2005 to November 2005.
Measurement of microbial enzyme activities and faunal feeding activity was performed in samples taken from the soil upper layer (3-15 cm).

Test substrate

Details on preparation and application of test substrate:

In September 2004, an aqueous solution of KH2PO3 (7.5 g P per m2) with mud flat soil (42% DM, 2.5 kg per m2) were mixed to a volume of 4 L per m2. The finished dispersion was spread evenly on the soil by a watering can an afterwards superficially rake in.
Control plots received only 4 L tap water per m2.
In April 2005, the application of 7.5 g P per m2 was repeated.

Test organisms

Test organisms (inoculum):

other: Mud flat soil from the North Sea shoreline near Husum, Germany

Study design

Total exposure duration:

60 wk

Remarks:

from Sept 2004 to Nov 2005

Test conditions

Test temperature:

ambient temperature throughout the year

Details on test conditions:

The existing grass sward was removed before the first soil treatment. Afterwards a new grass cover (Lolium perenne) was established.

Nominal and measured concentrations:

Dosing at 7.5 g phosphite per m2 resulted in an initial concentration of 841 mg/kg dw in the first soil samples. After the second application, measurements yielded maximum circa 60 mg phosphite per kg dw.

Results and discussion

Effect concentrations

Duration:

60 wk

Dose descriptor:

other: enzyme activities

Effect conc.:

75 kg/ha

Nominal / measured:

meas. (not specified)

Conc. based on:

test mat.

Basis for effect:

other: enzym activities and mesofauna feeding activity

Remarks on result:

other: Only mesofauna activity was significantly negatively correlated to soil phosphite content. Initial concentration peaked at 840 mg/kg, after repeated application the maximum reached 60 mg/kg dw.

Details on results:

Phosphite concentrations increased in the phosphiet treated plots and after the first phosphite application, the phosphate concentrations increased, after a lag phase. After the second phosphite treatment in April 2005 no delay was observed, oxidation of phosphite restarted immediately. This could be a sign of a well-adapted microbial community.

Any other information on results incl. tables

The microbial enzyme activity of dehydrogenase and alkaline phosphatase were significantly increased in the phosphite treated soils, by 21 and 28%, respectively.

The cellulase activity was decreased by 16% (not significant), while the protease activity remained contstant.

The combined phosphite/mud flat soil application significantly reduced the feeding activity of the soil mesofauna by 15%.

Applicant's summary and conclusion

Validity criteria fulfilled:

not applicable

Conclusions:

Phosphite applied in a mud flat soil suspension to soil was oxidised to phosphate after a lag phase. The combination of phospite and mud flat soil affected the faunal feeding activity. No significant correlations were found between microbial enzyme activitues and soil phosphite content. It was concluded that phosphite did not harm the biocoenosis of soil micor-organisms and soil mesofauna.

Executive summary:

The effect of phosphite on the biocoenosis of an arable soil was investigated in a field trial. The response of soil micro-organisms and mesofauna were studied. After application of phoshite in the form of KH2PO3, combined with nud-flat soil, to the upper layer of a grass grown plot, an adaptation of the metabolic activity of the active soil biocoenosis caused at least a partly oxidation of phosphite to phosphate.

Microbial enzyme activities demonstrated no significant correlation to soil contents of phosphite and phosphate with exception of dehydrogenase (correlated to phosphate). The mesofaunal feeding activity was significantly decreased after the application of the mixture of phosphite and mud flat soil.