Dizinc pyrophosphate

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Data waiving:

other justification

Justification for data waiving:

other:

Key value for chemical safety assessment

Koc at 20 °C:

1 100 000

Other adsorption coefficients

Type:

log Kp (solids-water in suspended matter)

Value in L/kg:

5

Other adsorption coefficients

Type:

log Kp (solids-water in soil)

Value in L/kg:

2.2

Additional information

Dizinc pyrophosphate is a slightly soluble zinc salt (WS: 12.871 mg test item/L at loading rate of 251 mg/L, 20 °C and pH 6.5 -6.7 ).  

The mobility of zinc in soil depends on soil properties like organic matter content, clay content, hydroxides and also factors like on soil pH and redox potential. The soil pH is an important factor influencing the adsorption and thus the mobility of zinc. The amount of zinc in solution increases with decreasing pH (WHO 2001). Data on the adsorption behaviour of zinc has been comprehensively reviewed EU Risk Assessment Report for zinc metal (ECB, 2008). In the report Kp values of 110,000 (logKpsusp=5.04) and 73,000 (logKpsed=4.86) L/kg were identified for zinc. The Kp values were adopted for the risk assessment for dizinc pyrophosphate.

Phosphate adsorption is affected by numerous factors, e.g. pH, type and concentration of electrolytes, clay content, Al and Fe oxides, and organic matter content (Razaq, 1989). At normal soil pH values of 4.5 - 6.2 the dominant species are H2PO4 - and HPO4 -2. These ions can be present in soil water and also absorb onto the surface (or adsorb into) solid matter in soil. Two types of inorganic reactions control the concentration of phosphate ions in solution; these are precipitation-dissolution and sorption-desorption processes. Precipitation-dissolution reactions involve the formation and dissolving of precipitates, which is significantly pH depended. Sorption-desorption reactions involve sorption and desorption of ions and molecules from the surfaces of mineral particles, such as Al/Fe oxides/hydroxides, clay minerals and carbonates (Parker et al., 1998). Sato et al. (2009) observed that phosphorus released from calciumphosphate was adsorbed to aluminium and iron-oxyhydroxides. Basically, phosphate adsorption dominates in mineral soil with a low pH.

 

Reference

European Chemicals Bureau (ECB), Risk assessment Zinc metal CAS-No.: 7440-66-6, EINECS-No.: 231-175-3, Final report, May 2008, EUR 24587 EN – 2010

Parker J.E., Robertson J., Wansbrough H. (1998) Chemical Processes in New Zealand, Bd 2. New Zealand Institute of Chemistry, 01.01.1998.

Razaq, Ibrahim Bakry Abdul (1989) Effect of pH and exchangeable metals on phosphate adsorption by soils. Retrospective Theses and Dissertations, Paper 9170.

Sato et al. (2009) Biogenic calcium phosphate transformation in soils over millennial time scales. Journal of Soils Sediments (2009) 9:194–205

WHO. 2001. Environmental Health Criteria Series 221: Zinc, International Programme on Chemical Safety, World Health Organization, Geneva