Calculations of trace-element fluxes to the ocean associated with a hypothetical 10-km-diameter Cl chondrite indicate that the mass of certain elements contained in the bolide, such as Fe, Co, Mn, Al, Zn, Ni, Ge, Cr, Sn, Cd, Pb, Ag, Cu, Hg, and Se, are comparable to or larger than the world ocean burden. Consequently, the introduction of meteoritic elements, in the form of atmospheric aerosol particles, to the surface ocean after a large meteor impact, concurrent with various element-specific solubilities, could rapidly alter the geochemical balance of some oceanic trace elements. We believe that this hypothetical pulse of trace elements would have been of sufficient magnitude to perturb the biogeochemical cycles operative at 66.4 Ma, a possible time of meteorite impact. Through direct exposure and bioaccumulation, many trophic levels of the marine food chain would have been adversely affected by these meteoritic elements. Those organisms residing in the surface ocean would be exposed to high prolonged concentrations of toxic trace elements. Preferential extinctions as driven by species-specific tolerance of elevated trace-element levels in the ocean would occur. The trace-element aerosol flux associated with K/T boundary volcanism may also have contributed to elevated trace-element concentrations in the world ocean. The trace-element toxification hypothesis postulates a mechanism that may have contributed to the selective extinction of marine organisms during the enigmatic terminal Mesozoic event.