Search

Both suspended and streambed sediments from two pairs of streams (intervention outlet and control outlet, and Branch 14 and Branch 15) in livestock intensive catchments were analyzed for total phosphorus (TP), algal available P (AAP), P fractions and P saturation index (PSI). The variations in sediment P characteristics associated with sediment type and study sites were investigated; and the key variables controlling the variations were explored. Relative to streambed sediments, suspended sediments had significantly higher storage of TP and AAP and greater potential to continue adsorbing P from the water column. The differences between the two groups of sediments mainly resulted from differences in sediment particle size. For both suspended and streambed sediments, concentrations of TP, AAP, organic P (Po) and inorganic P (Pi) were not significantly different between the two catchment outlets, but were significantly higher in Branch 15 than in Branch 14; PSI values were considerably higher in the control outlet than at any of the study sites within the intervention micro-catchment. Sediment properties (e.g., calcium (Ca), aluminum (Al) and organic matter (OM)) and catchment characteristics (e.g., soil M3P status and drainage area) explained 62–87% of the variations in log-transformed TP, AAP, Po, Pi and PSI in suspended sediments, with sediment properties being the main contributor. For streambed sediments, variations in P concentrations and PSI were less well explained (13–56%), and sediment OM was the most importance predictor. Forest area percentage in landscape explained limited (3%) proportion of the variations in streambed sediment P concentrations and PSI.

The adsorption of phosphorus on natural diagenetic iron (Feox) and manganese (Mnox) oxyhydroxides was studied in deep and littoral zone sediments of mesotrophic Lac Saint-Charles (46°56 N, 71°23 W), using a Teflon sheet technique for collecting diagenetically produced metal oxyhydroxides. Collected metal oxide amounts were greater at the deep-water station, relative to littoral zone stations reflecting sediment and local diagenetic differences. Two-layer surface complexation modeling on iron oxyhydroxide was consistent with the measured total P/Fe molar ratios except for the upper mixed Mn–Fe oxide layer from the littoral stations, where measured phosphorus exceeded the modeled phosphorus by more than fivefold. Soluble reactive phosphorus (SRP) exchange between oxyhydroxide samples and natural lake water in the laboratory revealed a labile phosphorus pool. Phosphorus determined on the Teflon sheets from the littoral zone stations appears to be related to a distinct non-humic organic carbon pool that readily exchanges SRP, while little exchange was observed from material collected from the deep-water station. We suggest that the enhanced SRP release from littoral zone sediments is due to an organic carbon and/or metal oxide-impoverished sediment matrix, limiting microbial oxide reduction and allowing phosphorus to be rapidly recycled at the sediment–water interface, instead of being slowly incorporated into humic material. The SRP fluxes revealed in our study, which originate from the solid phase at the sediment–water interface, would be difficult to resolve using interstitial pore-water samplers and might be a quantitatively important source of inorganic phosphorus in Shield lakes.

Swine wastewaters contain varied and high amounts of organic matter (proteins, antibiotic compounds, organic acids) which are difficult to oxidize biologically or chemically. The discharge of such effluents is undesirable and can cause excessive oxygen demand in the receiving water. In order to produce an effluent suitable for stream discharge, electrochemical techniques have been explored at the laboratory pilot scale, for refractory residual organic compound removal in liquid swine manure (LSM) following a biofiltration process. Two types of electrolytic cells (monopolar and bipolar electrode cells) using aluminum and mild steel electrodes were studied. Effectiveness was measured in terms of chemical oxygen demand (COD) and biological oxygen demand (BOD) reduction. The amount of residue sludge produced and energy consumed have been also considered. Results showed that the best performances of COD and BOD removal from LSM were obtained using either aluminum bipolar (Al-BP) electrodes or mild steel monopo...

The oxidation of volatile aqueous Hg0 in aquatic systems may be important in decreasing the fluxes of Hg out of the water column. Using incubations of natural samples from the St. Lawrence River, we examined some of the parameters that control this oxidation. Hg0 was found to be chiefly mediated by UV radiation since (i) "dark" oxidation was not found to be statistically significant; (ii) visible light induced a significant but slow photooxidation (k = 0.09 h(-1)); and (iii) visible + UV radiation led to a faster photooxidation (k = 0.6-0.7 h(-1)), mainly because of UV-A induced reactions. Doubling UV irradiation did not increase the reaction rate of Hg0 photooxidation in natural water samples, indicating that some factor other than photon flux was rate limiting and suggesting that the reaction involves intermediate photoproduced oxidant(s). The addition of methanol, a *OH scavenger, decreased Hg photooxidation rates by 25% in brackish waters and by 19% in artificial saline water containing semiquinones, indicating that *OH may be partly responsible for Hg0 oxidation. Photooxidation rates were not affected by oxygen concentrations and did not decrease when samples were heat-sterilized, treated with chloroform, or filtered prior to exposure to light.

Volatilization of elemental Hg represents an important Hg flux for many aquatic systems. In order to model this flux accurately, it is necessary to measure elemental Hg concentrations in air and water, as well as meteorological variables. Up to now, temporal resolution of elemental Hg analysis has been low (0.5–1 h between data points) compared to other variables used in models (5 min between data points). Here we present an analytical system that allows for the near-real time measurement (every 5 min) of dissolved gaseous mercury (DGM). This system is automated and has a detection limit of 8.5 pg l−1. By using solar radiation as a predictor of DGM concentrations in aquatic systems, we demonstrate the fast response time of the analytical system to fluctuations in ambient DGM in the St. Lawrence river, at sunrise. Complete covering of the purge apparatus and tubing resulted in a 2.6-fold decrease in the slope of the DGM versus light relationship, revealing the importance of light shielding the instrumentation to obtain realistic values.

We tested the hypothesis that phytoplankton productivity in pelagic Lake Erie is limited by low Fe bioavailability during the period of thermal stratification. Iron enrichment (20 and 200 nM Fe) of water sampled from the eastern basin surface water (5 m depth) in July 1996 revealed a dramatic 180 and 30% increase in the standing crop of the picoplankton (0.2-2 µm) and nanoplankton (2-20 µm) size fractions, respectively. Light-saturated rates of photosynthesis for picoplankton increased 2.8 times that of the controls within 24 h. In contrast, simultaneous P and Fe enrichment experiments carried out in July 1997 and August 1998 with water samples from three pelagic stations revealed that P enrichment alone stimulated phytoplankton growth, although at several stations, phytoplankton yield was greater in combined P- and Fe-amended experiments relative to P-enriched treatments. Periodogram analysis of meteorological buoy wave height data and heat budgets calculated from thermal profiles in the eastern basin revealed important interyear differences in precruise conditioning of the epilimnion. Low-frequency, turbulent mixing events that characterized the 30-day precruise period in the years 1997 and 1998 relative to 1996 may have prevented Fe-stressed conditions in the phytoplankton community studied in 1997 and 1998.

Alum sludge derived from a municipal wastewater plant was used as a soil amendment in a greenhouse study with barley (Hordeum vulgare) as the test crop. Treatment variables included the soil pH (4.5, 5.1 and 6.5), the amount of Al in the sludge (control = 30 mg AlT/g; alum sludges = 38 and 52 mg AlT/g), and the sludge application rate (100 and 270 kg NT/ha). Soil amendment with the two alum sludges reduced soil pH, increased Al3+ activity in the soil solution, and reduced barley growth over the 6-week experiment. Barley growth decreased as the Al3+ activity in the sludged soil solution increased, but for a given Al3+ the phytotoxicity of Al was markedly pH dependent. For example, at a pH of 5.0 ± 0.1 an Al3+ activity of 0.5 μM was sufficient to inhibit plant growth by about 50% this IC50 value increased five-fold to about 2.5 μM when the soil pH was 4.5 ± 0.1. This decrease in the toxicity of Al50 with acidification was explained in terms of a competitive interaction between the H+-ion and Al3+ at the root surface. Stepwise multiple regression allowed the prediction of aerial leaf biomass from soil pH and sludge application rate.

Phosphorus (P) release and flux at sediment-water interface was hypothesized to vary with studied catchment branches due to differences in water chemistry of recharging groundwater. Stream water, seepage water, groundwater, and resurgence groundwater were collected, and their dissolved reactive P (DRP) concentrations and related water chemistry variables (pH, dissolved oxygen, cations, and anions) were measured to identify P sources in seepage water and resurgence groundwater and to look into their impacts on stream water DRP. Results showed that the groundwater-carried P concentrations were negligible, and, thus, not a direct source of DRP to stream water. However, the upwelling groundwater could contribute to stream water DRP by dissolving calcite-bound P in top sediments of branch 15. The seepage experiment indicated that in branch14, sediment release of reducible P was minimal. Furthermore, the presence of impermeable clay layer over the streambed of branch 14 prevented the transport of water and nutrients from beneath sediments to stream water, further reducing the P flux across the sediment-water interface. This study revealed that in branch 14, the recharge of anoxic groundwater did not significantly influence stream water P, due directly to its low P concentration, or indirectly to the lack of reducible P and the poor hydrological connectivity in bottom sediments. These results showed that differences between P soluble concentrations in small catchment streams can be explained by physicochemical processes at the sediment-water interface. More investigation is needed to assess whole catchment P dynamics.

Rapid regeneration of ‘OgCd and 65Zn from their picoplankton prey into the dissolved phase by microzooplankton was observed in water sampled from the pelagic surface waters of Lake Erie (summer 1994 and 1995). Trace metals were added to grazing (lake water < 2’10 brn) and control (lake water CO.2 pm) treatments in the form of radiolabeled Synechococcus, Picoplankton (0.2-3 pm) were grazed heavily by consumers in the nanoplankton (3-20 pm) and microplankton (20-2 10 pm) size classes (collectively referred to as microzooplankton) as confirmed by dilution assays used to independently measure grazing activity. Most consumed trace metals were regenerated into the dissolved phase (x0.2 pm), but some trophic transfer of ‘OgCd and 65Zn from radiolabeled prey into the nanoplankton and microplankton did occur: 65Zn was transferred 2.5 times more efficiently into the microplankton and 2.9 times more efficiently into the nanoplankton than was logCd. Recycling of regenerated logCd back into plankton biomass was greater than that for 65Zn. Grazing by microzooplankton influenced the molecular size distribution of regenerated trace metal in the dissolved phase (77 + 6% log Cd

To test the response of the freshwater bivalve Pyganodon grandis (formerly Anodonta grandis) to increased metal exposure in the field, we transferred specimens (8 cm length; 4–6 years old) from a less to a more contaminated lake in the mining area of Rouyn-Noranda, in northwestern Québec. The transplanted bivalves were maintained in open enclosures placed in the bottom sediments of the contaminated lake. Up to 16 individuals were removed from pairs of enclosures at times t = 0 (June 1990), 5, 14, 30, 60, 90, and 400 d; tissue concentrations of metallothionein (MT) and metals were monitored over time. Measurements on control molluscs enclosed in their lake of origin showed that enclosure per se had no apparent effect on tissue [MT] or tissue metal levels, but did decrease shell growth. Metallothionein levels in specimens transplanted to the more contaminated lake showed a slow but steady increase with time; in contrast, MT levels in the control populations showed only modest seasonal fluctuations. The increase in MT over time in the transplanted bivalves was closely correlated with a similar slow increase in soft tissue [Cd]. We conclude that MT in the freshwater bivalve P. grandis is a promising biochemical indicator of metal exposure.

Metolachlor and atrazine are herbicides used in corn agriculture and detected in surface- and groundwater. Vegetated filters reduce masses of herbicides in runoff, but less attention has been given to their impact on degradation products and subsurface infiltrated water. The objective was to study the temporal evolution of dissolved metolachlor, atrazine and deethylatrazine concentrations in runoff and subsurface infiltrated water with two types of vegetated filters over 2 years for the first three rains following herbicide application. Runoff and subsurface infiltrated at 90-cm water samples from 12 plots of 30 × 5 m in a completely randomized block design of four replicates of three treatments-control without filter, 5-m-long grass filter, 5-m-long grass and tree filter were analysed using gas chromatography/mass spectrometry. Controls in runoff generally had the highest average atrazine, as high as 739 μg L−1, and metolachlor average concentrations, as high as 1,725 μg L−1. The first rain after application was mainly responsible for atrazine and metolachlor exports. Vegetated filters reduced concentrations of atrazine and metolachlor in runoff below their respective Canadian criterion of 1.8 μg L−1 for atrazine and 7.8 μg L−1 for metolachlor (provisory) (CCME 2002) for the protection of aquatic life when rain did not occur shortly after application. With the need to increase food production and agricultural yields to sustain the increasing world population came the need to develop efficient mitigation tools such as vegetated filter strips to reduce the ecotoxicologial impacts of pesticides. The present study is among the few that examined herbicide degradation products and subsurface infiltrated water under filter strips in order to provide new knowledge on the relationship between herbicide loss pathways and the environmental benefits of these strips. Such knowledge will provide much needed information to modellers, decision makers, ecotoxicologists and agronomists involved in the regulation, design and implementation of vegetated filter strips for the protection of water quality.

The microbial colonization of elemental sulphur in sewage sludge was studied by scanning electron microscopy (SEM). The indigenous sulphur-oxidizing microflora grown at the sulphur surface produces a filamentous matrix between the cells and the substrate. This material, similar to bacterial glycocalyx, confers to this biomass an ecological advantage allowing dense colonization. These adhesion structures were also observed with Thiobacillus thiooxidans ATCC 55128 growing in sewage sludge and in a synthetic mineral medium with Thiobacillus thiooxidans ATCC 19377 and Thiobacillus intermedius ATCC 15466 in synthetic medium. The production of this filamentous material was not observed with Thiobacillus thioparus ATCC 55127 cultured in sludge or in synthetic medium. The observation of these connections between cells and sulphur and among cells with the three acidophilic strains tested and with sulphur-oxidizing microflora indicate that this adhesion mechanism could play a significant role in sulphur colonization and oxidation in the natural environment.

Chemical and biological leaching of aluminum (Al) from redmud, the major waste product of the saline extraction of Al from bauxite, was examined. Sulfuric, citric, and oxalic acids were employed individually or as mixtures in chemical leaching experiments. The highest concentration extracted was 13 530 mg of Al/L (96% solubilization) using a 2:1 ratio of citric and oxalic acids and subsequent H 2 SO 4 addition to lower the pH to 1.5. Despite a lower concentration of extracted Al obtained with H 2 SO 4 alone at pH 1.0 (12 140 mg/L), it may be more economical due to the high price of organic acids

The presence of high concentrations of heavy metals in wastewater sludge is one of the most important factors that limit the application of sludge on agricultural land. In the last few years, the microbiological process of heavy metals removal from wastewater sludge has been studied in a batch mode. In the present study, the effects of metals, solids concentration, and initial pH on indigenous sulfur-oxidizing thiobacilli growth and metal solubilization were examined. The results obtained indicate that metals removal is possible even in high sludge solids concentration (70 g/L). The rate of sulfuric acid production through the oxidation of added elemental sulfur is increased by the increased sludge solids concentration.

Indigenous sewage sludge iron‐oxidizing bacteria was acclimated in twenty‐three different sludges to remove toxic metals from sewage sludge. The acclimation was carried out at pH 4.0 and 21 ± 1 °C. The required microflora was adapted in two to three successive transfers. The results showed that the oxidation of added Fe2+ in the form of FeSO4.7H2O decreased the sludge pH to 2.5 and increased oxido‐reduction potential (ORP) to 500 mV This pH reduction solubilized toxic metals to a level compatible with the recommended norms for agricultural use of the sludge. The adaptation of the microflora reduced the metal leaching period from 11–28 days to 2–10 days depending upon the sludge used. The metal leaching capacity of the adapted iron‐oxidizing bacteria was not significantly influenced by the sludge type (non‐digested sludge or aerobically or anaerobically digested sludge). Two strains of T. fenooxidans were isolated from sewage sludge, and their activity was compared with the standard strains of T. ...

Microbial leaching is one of the advantageous methods of removing heavy metals from sewage sludge, however, the microbiological aspects of this technology have not been studied. This study presents the characterization of the naturally occurring microorganisms, responsible for the metal leaching activity, in 21 different sewage sludges. The results obtained indicate that the bioleaching of metals is carried out by successive growth of less-acidophilic and acidophilic thiobacilli. Several species of less-acidophilic thiobacilli participate in the sludge acidification, but Thiobacillus thioparus is the most important species. In contrast, Thiobacillus thiooxidans seems to be the only species involved in the acidophilic group of thiobacilli. The growth kinetics of the two groups of thiobaciili was followed in five different sewage sludges. After 5 days of incubation in shake flasks, the pH of the sludge was decreased to about 2.0 and this pH decrease solubilized the toxic metals (Cd: 83–90%; Cr: 19–41%; Cu: 69–92%; Mn: 88–99%; Ni: 77–88%; Pb: 10–54%; Zn: 88–97%). The maximum specific growth rate (μmax) for the less-acidophilic thiobacilli varied between 0.079 and 0.104 h−1 and that for the acidophilic thiobacilli varied between 0.067 and 0.079 h−1.

Cadmium concentrations were measured at 49 littoral sites in 38 lakes distributed over 350,000 km2 in the provinces of Quebec and Ontario, both in the abiotic environment (oxic sediments and overlying water, diagenetic iron oxyhydroxide deposits on Teflon collectors) and in the soft tissues of the freshwater bivalve Anodonta grandis collected along a Cd contamination gradient. Concentrations of dissolved Cd above the water-sediment interface were highly undersaturated with respect to CdCO,(s). The partitioning of Cd between water and surficial oxic sediments is interpreted in terms of sorption of this metal to sedimentary organic matter and Fe oxyhydroxides, by means of surface complexation concepts. Binding intensity values for the sorption of Cd to Fe oxyhydroxides (&-& and organic matter (J&& are estimated from field data (i.e. Cd concentrations in diagenetic Fe deposits, in the sediments, and in the water). The following empirical relationships between binding intensities and lake pH are found: log K Fe-Cd = 0.82 pH - 1.30 (r2 = 0.89) and log Kc,M-Cd = 0.97 pH - 2.45 (r2 = 0.78). Calculated Cd partitioning with these binding intensities indicates that Cd is bound mainly to organic matter in these sediments. Linear regression analysis indicates that Cd concentrations in the soft tissues of the bivalves, [Cd(Org)] (pg g-l dry wt), are related to dissolved Cd concentrations: [Cd(Org)] = 44[Cd2+] + 10 (r2 = 0.81) for [Cd2 + ] expressed in nmol liter- I. In these lakes, simple normalization of sedimentary extractable Cd with respect to sedimentary Fe oxyhydroxide or organic C concentrations proved inadequate for predicting Cd concentrations in A. grandis. Combining surface complexation concepts with the free-metal ion model of trace metal-organism interactions, we show that Cd concentrations in the soft tissues of A. grandis can be predicted with similar success as with the dissolved Cd concentration from water pH and sediment chemistry (total sedimentary Cd, Fe oxyhydroxides, and organic C concentrations).

Bioleaching of metals can be achieved in sewage sludge using Thiobacillus ferrooxidans, which obtains its energy requirements from the oxidation of added ferrous iron. The purpose of this study was to verify the presence of indigenous T. ferroxidans and to evaluate their adaptive capacity and leaching potential. Nineteen sludges (primary, secondary, aerobically and anaerobically digested, oxidation pond) were tested and all of them contained indigenous iron-oxidizing bacteria. The acclimation of these organisms by successive transfers allowed a rise of sludge redox potential over 450 mV and a decrease of sludge pH between 3.8 and 2.2 over a 10-day incubation period. The metal solubilization efficiencies were Cd: 55-98%, Cr: 0-32%, Cu: 39-94%, Mn: 71-98%, Ni: 37-98%, Pb: 0-31% and Zn: 66-98%, were reached with these indigenous strains. The results obtained show that the metal bioleaching may be easily realized by direct acclimation of sludge microflora.

In many areas of intensive corn production, atrazine and metolachlor are among the most commonly found herbicides in surface and ground water. This 2-yr study compared the impact of grass and grass+tree buffer strips on the exported masses of atrazine, metolachlor, and a degradation product of atrazine, desethylatrazine (DEA). The experimental system consisted of four replicate plots in a three-way completely randomized design (no buffer zone, grass buffer zone, and grass+tree buffer strips). The field plots were 5 m wide and 30 m long and grown in corn. The grass and grass+tree buffer strips were 5 m and had the same grass vegetation except for eight young hybrid poplars. Over the 2-yr study, surface runoff and subsurface infiltration water (under the buffer strip) were collected after the initial three rainfall events after herbicide application. Dissolved atrazine, metolachlor, and DEA were analyzed by gas chromatography/mass spectrometry. The presence of buffer strips decreased the exported masses of atrazine and metolachlor in surface runoff. A three-way ANOVA with treatment (type of buffer strip), water (surface runoff or subsurface infiltration), and time between herbicide application and rainfall event as factors showed a significant reduction (40-60% in 2004 and 75-95% in 2005) in the total (surface runoff+infiltrated water) exported masses of atrazine and metolachlor in the presence of buffer strips. Rainfall events after herbicide application were different between the 2 yr and greatly affected the flow distribution (e.g., subsurface infiltration) and the leached herbicide concentrations. No significant difference in the capacity to reduce herbicide exports was observed between grass and grass+tree buffer strip treatments; the poorly developed young poplar biomass at the time of the study may partly explain this observation.

Twentythree different sewage sludges were studied to adapt indigenous sulfuroxidizing microflora to solubilize a substantial part of trace metals from the sludges. The results showed that the oxida...

The metal removal from municipal sewage sludge was studied by acid treatment and two microbial leaching processes in laboratory reactors. The leaching potential of the three processes tested were compared from results obtained on twenty-three sludges, and the influence of solids content and types of sludges was also investigated. The use of a microbial leaching process with elemental sulfur and or ferrous sulfate as substrate permits to reduce considerably the quantity of acid required for metal extraction with a reduction of 100 and 83% respectively. Bioleaching process with sulfur as substrate and sulfur-oxidizing bacteria (bioreaction time of 5 days) was revealed to be better than the acid treatment process and microbial leaching with ferrous sulfate and iron-oxidizing bacteria (bioreaction time of 10 days) for solubilization of all metals tested. Microbial leaching process with ferrous sulfate as substrate permits a better solubilization of cadmium, copper, manganese and zinc than the acid tratment with sulfuric acid (1 day, at pH 1.5). However, the solubilization of aluminium, chromium, nickel and lead was less than acid leaching.

A mixed culture of two fast-growing bacterial strains for heavy-metal solubilization of municipal sewage sludge has been developed. Strain VA-7 decreases the initial sludge pH (7–8.5) to a value between 4.0 and 4.5. Then, strain VA-4 begins growing and further reduces the pH to values below 2.0. The rapid decrease of sludge pH by a mixed culture through sulfur oxidation into sulfuric acid solubilizes the toxic metals (Cd 83–96%, Cr 16–54%, Cu 85–87%, Mn 91–94%, Ni 78–79%, Pb 28–46%, Zn 82–96%) to levels recommended for intensive use of residual sludge in agriculture. A study of the physiological and metabolic characteristics of these strains revealed that isolate VA-7 is a strain of Thiobacillus thioparus (ATCC 55127), while isolate VA-4 corresponds to a Thiobacillus thiooxidans (ATCC 55128). These bacterial strains possess distinctive physiological characteristics that allow them to easily grow and solubilize heavy metals in municipal sludge. Key words: heavy metals, sewage sludge, thiobacilli, bioleaching, elemental sulfur.

[1] This paper reports a net snow-to-air Hg transfer from the remote and temperate Experimental Lakes area (Ontario, Canada). More than 40% loss of total Hg concentration was observed in surface snow within 24 hours of its deposition on the ground. Stratigraphic profiles of total Hg in various snowpacks demonstrated a systematic decrease in total Hg concentration with snow depth pointing to snow-to-air Hg transfer and not snow-to-ground transfer. These results confirm observations made in a suburban area (Sainte-Foy, Quebec, Canada) receiving higher atmospheric deposition of Hg perhaps differently associated chemically. The occurrence of this phenomenon is therefore extended geographically to include snow from pristine regions. It is hypothesized that the loss of Hg is caused by a sunlight-initiated Hg(II) reduction in snow and subsequent gas transfer of Hg0 to the atmosphere. Polychromatic action spectra demonstrated that Hg(II) reduction in snow was mostly mediated by UV-B irradiation and not visible, or UV-A wavelengths. In addition to Hg(II) reduction in snow, we observed Hg0 oxidation in snow samples spiked with Cl−. Hg0 oxidation could limit the potential for Hg loss from snowpacks from coastal polar or subpolar regions (where snow often contains high chloride levels) by competing with Hg(II) reduction and slowing the snow-to-air Hg transfer. However, in regions under minimal marine influences, watershed budgets of Hg should consider the possibility of Hg loss from snow with time of deposition on the ground. Also, snow core studies should consider historic sunlight irradiation if extrapolation from snow cores is desired to estimate past ambient Hg levels.

As the isozymes of pyruvate kinase (PK) are best known in rats, the characteristics of the rat isozymes are generally used to classify the PK isozymes in other species. Given the discrepancies generated by this classification by analogy, we evaluated a classification using a phylogeny congruence analysis of the compositional relatedness of vertebrate PK's. While our phylogenetic analysis confirmed the well established separation of the L and R isozymes from the K and M isozymes, its power became most evident in the identification of non-orthologous (or variant) forms of PK. Our analysis emphasized the uniqueness of chicken liver PK which cannot be classified either as a K or an L isozyme, confirmed that tumors express a variety of forms of PK, and indicated that lungs systematically express PK's which are not orthologous with PK's from other tissues. The determination of orthology by the phylogeny congruence analysis assumes that the structural data from different sources are subject to similar methodological error. However, we cannot reject the possibility that an apparent lack of orthology be due to artifacts during purification and analysis.

Although 32P-uptake kinetics enable the closed mathematical treatment of the phosphorus cycle, several P pools, other than PO4, do not achieve isotopic equilibrium. This means that the P system could be open to P sources not labelled by the tracer. We tested whether such sources supporting an open system could produce significant changes in phytoplankton biomass in two lakewater communities. Two fractions were concentrated from natural lakewaters ranging from 2 × 103 to 104 daltons (fraction I) and 104–105 daltons (fraction II). These were then reintroduced to the natural communities at three concentration levels. During the incubation that followed, we assessed the capacity of the added organic matter to deliver phosphorus to the P cycle by monitoring known keypoints: phosphatase activity, 32PO4-uptake rate constant, and chlorophyll a. These measurements allowed us to estimate respectively the potential for hydrolysis, the actual product of hydrolysis PO4 (which disrupts 32PO4-uptake rates) and the long-term net uptake of P (growth). Although the fractions did cause decreases in growth, and also increased both phosphatase activity and PO4 uptake rate constants, none of these could be attributed to an additional delivery of P to the community. Under all conditions tested, the P system remained closed to organic P additions. However, the observed effects could be explained by non P organic matter such as dissolved humic materials acting either directly upon the community, or on phosphorus kinetics. The effects appeared to be pH dependent. We suggest that outside Spring P loading or other sporadic P inputs, the natural community tends to operate within a closed P system, where community dynamics are more strongly affected by non P organic matter than by organic phosphate inputs.

Recovery responses to toxicants are neglected in screening and hazard assessment studies which use primary producers as test microorganisms. In this study both structural and functional biotic variables of Selenastrum capricornutum populations are proposed to diagnose cellular stress and to predict recovery responses. The industrial effluent had greater short-term effects on both photosynthetic efficiency (P/B ratio) and adenylate energy charge (EC A ) than did cadmium. With both toxicants high P/B ratios and EC A are observed at the end of the experiment when cell densities are still low, suggesting that these functional parameters can be useful in the detection of recovery responses to toxicants. EC A appears to remain low only under conditions of acute stress. The variation of ATP/cell during the 96 h of the exposure experiment is proposed as an indicator tool for predicting short-term recovery in hazard assessment studies.

Surficial sediment samples and specimens of a benthic freshwater pelecypod, Elliptio complanata, were collected at eight sites located along a metal contamination gradient downstream from the mining and smelting complex in Rouyn–Noranda, Quebec. The molluscs were dissected, digested, and analysed for Cu, Pb, Zn, Fe, and Mn by flame atomic absorption spectrophotometry. Each sediment sample was wet sieved and the

Microbial and phytoplanktonic processes of a perturbed river system were evaluated as an ecotoxicological alternative to bioassays in hazard assessment of industrial wastewater discharge. Although phytoplankton species composition was invariable throughout the river gradient, both P/B and ATP/AMP ratios revealed that the community did not acclimate over the spatial scale studied. The adenylate energy charge (ECA) of the microbial community decreased at the station where the wastewater is discharged; however, no significant differences in (ECA) values were observed downstream. Enclosure experiments allowed us to conclude that the microbial community was predominantly affected by the effluent rather than by the lotic physical gradient. In the river gradient, ECAappears to be an insensitive metabolic indicator; however, small changes in ECAare accompanied by much larger changes in the ATP/AMP ratios to which enzymatic activities are responding. The fact that some functional metabolic processes of the microbial community were affected while phytoplankton species composition was invariable suggests that P/B and ATP/AMP ratios would prove useful in the detection of insidiuous effects of industrial effluents at the microbial community level. This approach could also give more insight into the ecological significance of wastewater discharge for monitoring purposes.

The separation of the various phosphorus compounds present in lakewaters is needed to assess their availability and role in algal assemblages. Separating these compounds by gel chromatography can take several hours, and denaturation can occur during that time. It is possible to accelerate the procedure by using several batch extractions in sequence. The method described allows the simultaneous analysis of 4 samples in about 20 min. This gain in time is obtained at the expense of resolution since the whole elution profile is spread over 10 samples. This method was found simple and efficient in applications where the speed of separation is more important than resolution.