Recent declines in PAH, PCB, and toxaphene levels in the northern Great Lakes as determined from high resolution sediment cores.

Sediment cores were collected from two sites in Grand Traverse Bay, Lake Michigan in May 1998, dated using 210Pb geochronology, and analyzed for polychlorinated biphenyl (PCB) congeners, polycyclic aromatic hydrocarbons (PAHs), and toxaphene. The extraordinarily high sediment focusing and accumulation rates in these cores relative to other Great Lakes sediments allowed quantification of high-resolution temporal trends in the burial of hydrophobic organic contaminants. The focus-corrected accumulation rate of total PCBs (sum of 105 congeners) in 1998 was 0.50 ng/cm2-year at both sites. Toxaphene and total PAH (t-PAH; sum of 33 compounds) surficial accumulations varied at each site and ranged from 0.08 to 0.41 ng/cm2-year for toxaphene and 25 to 52 ng/cm2-yr for t-PAHs at the two sites. The maximum t-PAH accumulation rate was in sediment dated from 1942, and PAH accumulation decreased from 1942 to 1980 with a first-order rate of decline 0.017 yr(-1). Both toxaphene and t-PCB accumulations peaked in sediment deposited in 1972, afterwhich their accumulations decreased with nearly identical rates of decline (0.027 yr(-1) and 0.028 yr(-1), respectively).