Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 1/5)
Character Range: 1611399–1614367

6                   DDT

6.1              Compounds considered
DDT is the abbreviation used for dichloro-diphenyl-trichloroethane (C14H9Cl5). Technical grade DDT (the form used in pesticide formulations) consists of 14 compounds (ATSDR 2002). The active ingredient and the main constituent of DDT is p,p'-DDT (approx 87% of DDT). Other compounds present include o,p'-DDT (15% of DDT), dichloro-diphenyl-dichloroethylene (DDE) and dichloro-diphenyl-dichloroethane (DDD), which are also metabolites and breakdown products of DDT. When DDT is referred to, usually people are referring to p,p'-DDT and this was the form that was used for the derivation of the EIL. The CAS registration number for p,p'-DDT is 50-29-3.

6.2              Pathway risk assessment
Selected physicochemical properties of DDT include:
Molecular weight  354.49 (Howard & Meylan 1997)
Log Kow   6.91 (Howard & Meylan 1997; Hansch et al. 1995)
Log Koc   5.18 (Swann et al. 1981)
Vapour pressure   1.60 x 10-7 at 20°C (Bidleman & Foreman 1987)
Aqueous solubility   0.025 mg/L at 25°C (Howard & Meylan 1997),
                   5.5 x 10-3 mg/L at 25°C (Yalkowsky & Dannenfelser 1992)
Henry's law constant  8.3 x 10-6 atm-m3/mol (Howard & Meylan 1997)
                  Half-life (in aerobic soil)  range from 2 years (Lichenstein & Schulz 1959) to greater than 15 years (Keller 1970; Stewart & Chisholm 1971)
Half-life (in anaerobic soil) 16100 days (Castro & Yoshida 1971)
Half-life of DDT  190 years (OMEE 1993)
Bioconcentration factor 2.516 (CCME 1999d)
Bioaccumulation factor 0.929 (CCME 1999d)
DDT is a well known biomagnifying contaminant and, as the log Kow is higher than 4, both the direct toxicity and biomagnification routes of exposure needed to be accounted for in deriving the SQGs. Therefore, the level of protection (that is, percentage of species to be protected) was increased for urban residential/public open space soils from 80% to 85% as recommended in Schedule B5b. The log Koc value for DDT is >5 and therefore there is a very low potential for DDT to be leached to groundwater or surface water.

6.3              Toxicity data
The raw toxicity data available for DDT is presented in Appendix F. The geometric means of toxicity data for each species and soil process are presented in Table 42. There was toxicity data for a total of 15 species or soil processes that belong to 5 different taxonomic groups or nutrient groups. Thus, there was sufficient toxicity data to use the SSD method to derive SQGs for DDT.

6.4              Normalisation relationships
As with naphthalene, it is well known that the organic carbon or organic matter content of soils affects the toxicity and bioavailabiity of organic contaminants such as DDT. However, there were no normalisation relationships available for DDT. Therefore, the toxicity data could not be normalised to the Australian reference soil (Table 6), nor could soil-specific SQGs be derived.

6.5              Sensitivity of