Chloroform–methanol (2:1, v/v) extracts significantly more (P < 0.001) chlorophyll a from algal cultures and from freshwater and seawater microcosms than does dimethyl sulfoxide, methanol, absolute methanol with hydrogen sulfide, or 90% acetone. For chlorophyte cultures it yields 97% or more of the chlorophyll a within a 4-h steeping period without grinding. It can be used with both calibrated spectrophotometry and fluorometric instrumentation. Sample filtration onto MgCO3-coated filters is recommended to ensure buffering of the extraction mixture. Holding the filters in chloroform–methanol at 4 °C or room temperature in the dark prevents loss of chlorophyll a for at least 10 d. More refined analyses of phaeophytin and other chlorophylls require the use of chloroform–methanol–water (2:2:1.8, by volume) and placement in a separatory funnel. After 24 h the lower (chloroform) layer contains all of the chlorophyll. Strict pH control is required for pheophytin determinations.

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Cycling of glucose at the sediment–water interface was determined through coupling measurement of natural substrate concentrations with heterotrophic uptake by the natural microbial communities in the sediment and in the water column. The same general pattern was found for both polluted and less polluted parts of Toronto Harbour, so that other labile organic species possibly have similar cycles. Velocity of uptake of glucose (flux) and turnover time showed no relationship to either substrate concentration or total organic matter of the sediments. Activity in the water column could be supported to a major extent by sediment export of substrate by turbulent diffusion. Sediment activity must be supported by particulate sedimentation and hydrolysis of large organic molecules, which may be aided by the macrobenthic community. Pollution stress apparently alters the catabolism of the substrate. The observed substrate concentrations may reflect a minimum of residual concentration, below which the microbial community has difficulty in taking up the substrate.

Abstract-Larvae of the aquatic insect Chironomus tentans (Insecta: Diptera: Chironomidae) were exposed at the third or fourth instar stage to sediments collected near the outfalls of two aluminum foundries and an aluminum fabrication plant. Biota and sediment bioaccumulation factors (BFs), based on wet tissue weights and dry sediment weights, ranged from 0.07 to 0.27 for polycyclic aromatic hydrocarbons (PAHs) and from 0.22 to 1.42 for polychlorinated biphenyls (PCBs). A higher rate of metabolism of PAHs compared with PCBs could explain the differences in BF values for the two groups of chemicals. It was found, using community similarity procedures from the field of ecology, that the congener patterns for PAHs and PCBs bioaccumulated by the larvae differed from the pattern of the same compounds in the sediments to which they were exposed. Affinity analysis indicated that the larvae favored the higher molecular weight PAH and PCB congeners. Preferential ingestion of sediments with defined particle size ranges, metabolism, and octanol/water partition coefficients (log K ow ) are factors that may have influenced the bioaccumulation patterns. However, no single factor could adequately account for the differences between the larval and sediment patterns.

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