HISTORY OF TOXIC METAL DISCHARGE TO SURFACE WATERS OF THE ABERJONA WATERSHED

A history of waterborne export of toxic metals from the industrial/res idential Aberjona Watershed, north of Boston, MA, has been reconstruct ed from an analysis of sediment cores from the Upper Mystic Lake, toge ther with historical records of industrial activity on the watershed. The lake sediments exhibit complex profiles of arsenic, cadmium, chrom ium, copper, lead, and zinc. These profiles are interpretable in terms of historical industrial activities on the watershed and transport vi a the Aberjona River to the Upper Mystic Lake. High concentrations (in excess of 1000 mg/kg arsenic and chromium) occur in two zones, at dep ths between 25 and 35 cm and between 50 and 70 cm in the sediments of this lake. The deeper zone corresponds to the early 1900s, a period of intense industrial activity during which chemical and leather industr ies are known to have made direct discharges of metals to surface wate rs. Sharp decreases in metals concentrations subsequently occurred as industry declined, and concurrently, much of the watershed was sewered in the mid-1930's. The more recent period of metals transport to the lake, which occurred ca. 1960, evidently was the result of remobilizat ion of wastes deposited on the watershed decades earlier.