Potential Effects of Dissolved Organic Carbon DOC on SPMD Calibration Data

POTENTIAL EFFECTS OF DISSOLVED ORGANIC CARBON (DOC) ON SPMD CALIBRATION DATA 

SPE sampling of 6 C-associated residues cannot be ruled out. Also, no data are available on the potential of the surficial retention of colloids or DOC by the SPE sorbent. These factors would lead to an overestimation of dissolved concentrations. Other sampling equipment may also yield inaccurate measurements of dissolved concentrations. Pre-equilibration of laboratory exposure systems is a separate issue related to attainment of steady-state water concentrations in the exposure system prior to initiation of the test. Clearly, the issue of DOC or colloidally sorbed contaminants deserves additional discussion. 

Recently, Burkhard (2000) reviewed contaminant sorption by dissolved organic matter. Using several hundreds of UCC-water partition coefficients (A doc) reported in these studies, he found that UCC-water partition coefficients for naturally occurring DOC (humic and fulvic acids, sediment pore water, soil pore water, groundwater, and surface water) was best described by 

The 95% confidence interval amounted to 1.3 log units, which corresponds to a scatter in the ATdoc values by a factor of 20. Burkhard (2000) argues that the uncertainty in Eq. 3.25 originates partly from inter-laboratory variation, and partly from differences in DOC quality. In view of the wide range of DOC sources included in Eq. 3.25, it does not seem likely that the uncertainties in any ATdoc encountered would be more than 1.3 log units. Hence, the worst-case estimate (maximum sorption of dissolved phase residues by DOC) can be described by 

When DOC-bound residues are extracted along with the dissolved phase (i.e., the total concentrations are measured), then the ratio of the truly dissolved concentrations (Cw) to the total concentration (Q) of an HOC can be estimated by 

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