PCBS IN THE DETROIT RIVER WATER COLUMN

Water samples (60 to 190 L) were taken from the Trenton Channel portio n of the Detroit River during eight sampling events from March to Octo ber 1995, and in May 1996. Samples were filtered on-site or at the fie ld-lab to retain the suspended particulates. Some of the samples were passed through XAD-2 columns to extract dissolved PCBs, depending on t otal samples volume and logistical consideration. Concentrations of po lychlorinated biphenyls (PCBs) were measured in both the particulate a nd dissolved fractions. Concentrations ranged from < 5 to 22 ng/L (ave rage = 10 ng/L) in the particulate, and from < 5 to 13 ng/L in the dis solved fractions. The average ratio of dissolved PCB concentration to particle-bound PCB concentration was 0.6; the calculated average total PCB concentration was 17 ng/L. Annual mass transport of PCBs through the Trenton Channel in 1995 was estimated to be 600 kg, with potential point sources along the west shore of the channel contributing less t han 1.5% of the total mass of PCBs. A general seasonal trend was obser ved, with lowest PCB concentrations in March and greatest in July. Con centrations following a significant rainfall increased within the firs t 24 hr and decreased to approximate ambient levels after 96 hr. In ge neral, PCB concentrations appear to be greater downstream than upstrea m, however, this trend was reversed for Day-1 of the rainfall events, perhaps due to greater particulate loading from upstream of the channe l. Potential point-sources from industrial or municipal waste-water tr eatment outfalls showed PCB concentrations up to a factor of 4 greater than those from the transects in the channel. However, the annual loa ding of PCBs to the channel. Dissolved concentrations of PCBs determin ed by C-18 Empore disks were 4.7-fold greater than those determined by XAD-2 (s.d. = 1.5, n = 4). Further investigations validating this fin ding are necessary. For this reason, comparisons among different studi es must be done with caution.