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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Conclusion: DTDP has the potential to sorb to organic matter to a great extent.

Key value for chemical safety assessment

Additional information

Sediment partition coefficients were measured for DTDP using an experimental procedure based on the U. S. Environmental Protection Agency (EPA) Test Guideline 796.2750, "Sediment and Soil Adsorption Isotherm." Three sediments were used: EPA 8 (0.15% organic carbon), EPA 18 (0.66% organic carbon), and EPA 21 (1.88% organic carbon). The Freundlich equation was used to calculate the organic carbon-normalized sediment/water partition coefficient (Koc), which averaged 1.20 E6 for DTDP. In general, these Kocvalues did not correlate well to either sediment or chemical properties. This lack of correlation suggested that the measured Kocvalues are suppressed, potentially as a function of experimental conditions. On the basis of these data, it was decided to investigate the dependence of Kocon sediment solids concentration and dissolved organic carbon. Analysis of these and earlier reported partition coefficient data indicated that measured Kocvalues for phthalate esters obtained in shake-flask experiments exhibited an inverse dependence on solids concentration. These results were consistent with partitioning models that are discussed. Depending on compound hydrophobicity, the particle-corrected Kocvalues were from one to three orders of magnitude higher than the measured Kocvalues. Therefore, if partition coefficient values obtained by using Test Guideline 796.2750 or similar shake-flask procedures are not corrected for solids effect, the estimates of the sediment pore-water concentration of the chemical is likely to be overestimated.

A mean Kocvalue for DTDP of 1,200,000 l/kg (log Koc= 6.08) was determined with a radiolabeled 14C-DTDP in experiments using the three different sediments with organic content ranging from 0.15 to 1.88% (Williams et al., 1995). The OECD guideline used to measure this endpoint suggests the use of soil with an organic carbon content range of 0.6 to 3.5%.

Sediment characteristics and Kocvalues from Williamset al. (1995)

Sediment Type

OC (a)








CEC (b)

(meq/100 g)




EPA 8 (c)







7.38 x 105

EPA 18







2.84 x 106

EPA 21







1.89 x 106

a  Organic carbon

b  Cation exchange capacity

c  U.S. Environmental Protection Agency soil type

In this test, the coefficient of variation for Kocwas similar to that observed for Kd despite a tenfold difference in organic carbon content between the three sediments investigated. This suggests that factors in addition to sediment organic carbon are influencing partitioning behavior.