Calcium hydrogen phosphonate

Toxicity to terrestrial plants

Administrative data

Endpoint:

toxicity to terrestrial plants: long-term

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Published paper with extensive description of methods and results.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2006

Materials and methods

Principles of method if other than guideline:

Studies on effect of fertiliser combinations

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Potassium dihydrogen phosphite KH2PO3

IUPAC Name:

Potassium dihydrogen phosphite KH2PO3

Test material form:

other: solution

Details on test material:

0.2% w/v solution

Sampling and analysis

Analytical monitoring:

yes

Details on sampling:

sampling of plant material

Study design

Test type:

other: biomass production

Study type:

extended laboratory study

Substrate type:

other: cleaned gravel sand amended with fertiliser

Total exposure duration:

90 d

Test conditions

Details on test conditions:

Pot experiments carried out in Mitscherlich pots (columetric capacity 8 kg).
Cleaned gravel sand as substrate.
Three groups: 1: KH2PO4 added (1008 mg P per pot);
2. KH2PO3 added (1008 mgP per pot)
3. No P added
Alle other nutrients were adjusted for optimum supply.
12 replicates per treatment.

28 days after seeding, plant density was reduced to 4 plants per pot and group of 12 replicates was split into three soil/foliar fertilization treatments. KH2PO3 was applied in a 0.2% w/v solution. The solution was applied on the 3 youngest fully developed leaves by means of a paint brush. This was repeated 4 weeks later on the healthy growing plants. Plants were harvested after 90 days. Production of plant material was determined.

Results and discussion

Effect concentrations

Species:

Zea mays

Duration:

90 d

Dose descriptor:

other: significant inhibition

Effect conc.:

700 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: Phosphonic acid

Basis for effect:

other: growth and habitus

Remarks on result:

other: 1008 mg P added per pot of 8 kg wet weight. Assuming a water content of 20% (EUSES), this converts to 158 mg P per kg dry soil. MW Ratio H3PO3/P is 4.4. Thus the concentration in soil is estimated at circa 700 mg Phosphonic acid H3PO3 per kg dry soil.

Any other information on results incl. tables

Plants supplied with phosphite were smaller than control plants which did not receive any P-fertilisation.

Phosphite fertilised plants showed an abnormal habitus. They developed lateral tillers with brightened, malformed leaves.

When the nutritional status of the plant wast optimal, additional phosphite foliar fertilisation yield no effect.

However, in P-starved maize, foliar application of phosphite resulted in a lower yield (DM) as compared the control. Additional foliar application of K-phosphite (0.2% w/v solution) caused irreversible foliar injuries

Effect of different P-fertilisation treatments on the dry matter yield of maize (g DM)

Substrate P fertilisation	Foliar P fertilisation
	Without	Phosphate KH2PO4, 15 mg P in 0.2 w/v solution	Phosphite KH2PO3, 15 mg P in 0.2 w/v solution
	Dry Plant Material [g/pot]
Without	9 b	25 c	4 a
optimum P supply by KH2PO4	54 a	59 b	54 a
optimum P supply by KH2PO3	4 b	5 b	1 a

All values are means of 4 replicates. Means followed by dissimilar letters in rows are significantly different (Duncan's test, P = 0.05)

Phosphite was shown to be well absorbed by plant roots as well as through foliar absorption. Phosphite is obviously stable within the plant metabolism process as only small amounts appeared to be oxidised to phosphate.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Remarks:

Test with sufficient controls

Conclusions:

The reduced growth observed in phosphite treated plants was especially evident under conditions of P-deficiency. This could result from a suppression of the natural mechanisms of plants to respond to P-deficiency.

Executive summary:

The efficiency of Potassium phosphite as P-source for maize plants has been studied in (among others) a pot experiment.

An inhibited growth was observed when phosphite was applied as the sole P-source (as compared to the control). The negatice effects ranged from a stunted growth of the plants to the complete die off. This effect was not observed or lower when phosphite was applied to maize under sufficient P-nutrition.

The detection of phosphite in the harvested maize plants also indicated that an oxidation to phosphate did not occur. Hence, Phosphite was not available to the plants as a P-source.

The concentration of phosphite in the soil was estimated at 700 mg (H3PO3) per kg soil dw.