Elemental mercury, Hg(0), is ubiquitous in water and involved in key Hg biogeochemical processes. It is extensively studied as a purgeable dissolved species, termed dissolved gaseous mercury (DGM). Little information is available regarding nonpurgeable particulate Hg(0) in water, Hg(0) bound to suspended particulate matter (SPM), which is presumably present due to high affinity of Hg(0) adsorption on solids. By employing stable isotope tracer and isotope dilution (ID) techniques, we investigated the occurrence and quantification of particulate Hg(0) after Hg(0) being spiked into natural waters, aiming to provide firsthand information on particulate Hg(0) in water. A considerable fraction of (201)Hg(0) spiked in water (about 70% after 4 h equilibration) was bound to SPM and nonpurgeable, suggesting the occurrence of particulate Hg(0) in natural waters. A scheme, involving isotope dilution, purge and trap, and inductively coupled plasma mass spectrometry detection, was proposed to quantify particulate Hg(0) by the difference between DGM and total Hg(0), determined immediately and at equilibration after spiking ID Hg isotope, respectively. The application of this newly established method revealed the presence of particulate Hg(0) in Florida Everglades water, as the determined DGM levels (0.14 to 0.22 ng L(-1)) were remarkably lower than total Hg(0) (0.41 to 0.75 ng L(-1)).