An interlaboratory comparison study for the determination of dialkyl phthalate esters in environmental and biological samples.

A series of interlaboratory comparison exercises were conducted to assess the accuracy of dialkyl phthalate ester (DPE) concentration measurements in environmental and biological samples. Five laboratories participated in analyses to determine DPE concentrations in standard test solutions; marine sediments; three certified reference materials, including CARP-2 (fish muscle) and BCR-07 (fortified milk powder); and several livestock samples (sheep's milk, liver, and muscle). In addition, one laboratory determined DPE residue concentrations in 20 municipal sewage sludge samples, previously analyzed as part of the 2006/2007 U.S. Environmental Protection Agency's Targeted National Sewage Sludge Survey (TNSSS). The results showed relatively good interlaboratory agreement for analyses of di-ethylhexyl phthalate (DEHP). Three independent laboratories (Labs A, B, and C) reported concentrations of DEHP (ng/g wet wt) in fish muscle (CARP-2) of 1,550 ± 148, 1,410 ± 193, and 1,380 ± 187, respectively. Similarly, DEHP concentration measurements in sewage sludge samples showed good agreement with those reported in the 2006/2007 TNSSS report. Measured concentrations of individual DPEs and C6-C10 isomeric mixtures in these samples of municipal sewage sludge, which have not been previously reported, ranged between 1 and 200,000 ng/g dry weight. The results demonstrate that environmental monitoring of DPEs is often hampered by high method detection limits (MDLs), due to contamination of procedural blanks. It is important to note, however, that when background contamination is minimized (<10 ng/sample), relatively low MDLs (<0.1 ng/g) can be achieved, allowing for low-level quantification of DPEs in environmental and biological samples. Future efforts to develop better protocols to lower MDLs, as well to develop reference materials, would greatly benefit future DPE monitoring initiatives.