From January t o July, 1972, six municipal sewage treatment plants were routinely monitored for the efficiency of heavy metals removal. municipalities served ranged from a small agricultural community to an industrial city. Four basic plant types were studied: 1 ) Primary w i t h sludge digestion; 2) Primary w i t h sludge f i l t r a t i o n ; 3) Trickling-filter secondary w i t h sludge digestion; and 4) Activated-sludge secondary with sludge digestion. Composite samples from the influent, effluent, and sludge were homogenized, acid-digested, and analyzed by atomic absorption spectrophotometry f o r Cd, Cr, Cu, Zn, and Pb. The efficiency of heavy metals removal and the relationship between heavy metals removal and suspended solids removal are discussed.

Selenium (Se) has long been known as an effective antagonist for counteracting mercury (Hg) and arsenic (As) toxicity in many animal and plant species. This study is the first to assess a low-dose Se additive as an in situ remediation tool for As-and Hgcontaminated gold mine tailing material. Mine tailing material from an 1860s gold mine stamp mill site was treated with different concentrations of sodium selenite (0, 0.5, 1, 3, 8, and 15 mg Se/kg). Reclamation grass seeds planted in each treatment showed significantly decreased plant toxicity with increasing [Se], as measured by increases in biomass, % emergence, and root lengths. Leachate was collected from each pot after the grass was harvested. The lowest Hg and As concentrations measured in the leachate were associated with the 1 mg Se/kg treatment (94 and 71 % lower than concentrations in leachate from untreated tailing material) and increased with lower and higher Se treatments. Finally, earthworms (Eisenia andrei) were introduced to the experimental treatments. Earthworm [Hg] decreased with increasing [Se], but this effect was confounded by differing [Hg] in the tailing material. Earthworm [As] decreased with [Se] up to 3 mg Se/kg, then earthworm [As] increased with tailing [Se]. This experiment confirms that low-dose selenium additions (up to 3 mg Se/ kg tailing material) can have beneficial effects by limiting toxicity and mobility of As and Hg from the tailing material for both grass and earthworms.