A test procedure has been designed to determine diffusion of organic contaminants from monolithic materials. The method is based on the use of a scavenger with a high sorption capacity which allows a near zero aqueous concentration and there by achieves a maximum diffusion gradient from the test object. Critical factors in the procedure have been tested using PAH as model compound. Long-term contact with storage vessel, transfer of organic contaminants to the scavenger and recovery from scavenger have been investigated.
The results showed that the glass storage vessel can sorb considerable amounts of PAH from solution in the initial phase of the test even at low aqueous concentrations. This is especially critical for the high molecular weight compounds, and can influence the outcome of the test.
Transfer of organic compounds from solution to the scavenger Tenax TA was strongly influenced by mechanical mixing of the aqueous phase. Tenax in granular form was highly effective in removing all PAH from solution provided sufficient mixing. Tenax as filter disc could not remove sufficient amounts from the solution even after extended contact times.
Different test materials have been assessed for testing the various procedures. Asphalt cores containing coal tar showed highly variable results which made them unsuited for this comparison. Clay pidgeons contained high amounts of PAH however the release rates were very low even when stirring was applied.
Since mechanical mixing will disturb the basic test requirement of a diffusion test a modified procedure was developed based on 1-D diffusion using an organic solvent (Cyclohexane) as scavenger. This procedure was tested with homogenised PAH contaminated sediments over a long time period. Stable and reproducible diffusion data were obtained for several PAH compounds.
The modified 1-D diffusion procedure has several advantages; short diffusion pathway from surface to scavenger, Completely closed system and Long-term stability (360 days). However mechanical modifications are required to be able to apply the methods on monolithic materials or construction waste.