Copper Release, Speciation, and Toxicity Following Multiple Floodings of Copper Enriched Agriculture Soils: Implications in Everglades Restoration

This study characterizes the effects of water–soil flooding volume ratio and flooding time on copper (Cu) desorption and toxicity following multiple floodings of field-collected soils from agricultural sites acquired under the Comprehensive Everglades Restoration Plan (CERP) in south Florida. Soils from four field sites were flooded with three water–soil ratios (2, 4, and 6 [water] to 1 [soil]) and held for 14 days to characterize the effects of volume ratio and flooding duration on Cu desorption (volume ratio and flooding duration study). Desorption of Cu was also characterized by flooding soils four times from seven field sites with a volume ratio of 2 (water) to 1 (soil) (multiple flooding study). Acute toxicity tests were also conducted using overlying waters from the first flooding event to characterize the effects of Cu on the survival of fathead minnows (Pimephales promelas), cladocerans (Daphnia magna), amphipods (Hyalella azteca), midges (Chironomus tentans), duckweed (Lemna minor), and Florida apple snails (Pomacea paludosa). Acute tests were also conducted with D. magna exposed to overlying water from the second and third flooding events. Results indicate that dissolved Cu concentrations in overlying water increased with flooding duration and decreased with volume ratio. In the multiple flooding study, initial Cu concentrations in soils ranged from 5 to 223 mg/kg (dw) and were similar to Cu concentration after four flooding events, indicating retention of Cu in soils. Copper desorption was dependent on soil Cu content and soil characteristics. Total Cu concentration in overlying water (Cu_w) was a function of dissolved organic carbon (DOC), alkalinity, and soil Cu concentration (Cu_s): log(Cu_w)?=?1.2909?+?0.0279 (DOC)?+?0.0026 (Cu_s)???0.0038 (alkalinity). The model was validated and highly predictive. Most of the desorbed Cu in the water column complexed with organic matter in the soils and accounted for 99% of the total dissolved Cu. Although total dissolved Cu concentrations in overlying water did not significantly decrease with number of flooding events, concentrations of free Cu²⁺ increased with the number of flooding events, due to a decrease in DOC concentrations. The fraction of bioavailable Cu species (Cu²⁺, CuOH⁺, CuCO₃) was also less than 1% of the total Cu. Overlying water from the first flooding event was only acutely toxic to the Florida apple snail from one site. However, overlying water from the third flooding of six out of seven soils was acutely toxic to D. magna. The decrease in DOC concentrations and increase in bioavailable Cu²⁺ species may explain the changes in acute toxicity to D. magna. Results of this study reveal potential for high Cu bioavailability (Cu²⁺) and toxicity to aquatic biota overtime in inundated agricultural lands acquired under the CERP.     

Comparison ofDaphnia magna,rainbow trout and bacterial-based toxicity tests of Ontario Hydro aquatic effluents

Over a one year program of intensive monitoring of effluents from Ontario Hydro's nuclear, fossil and hydroelectric generating facilities, theDaphnia magna and rainbow trout,Oncorhynchus mykiss, acute toxicity tests correlated well, with 61 % of the toxic effluents toxic to both species. If the effluent was toxic to only one of the test species it was generally toxic toD. magna, with from 23 to 57% of the toxic effluents toxic toD. magna only. The greater sensitivity ofD. magna to boiler blowdown effluent likely resulted from a combination of the low conductivity of boiler blowdown effluent and the smaller size and greater surface to volume ratio ofD. magna relative to rainbow trout.D. magna were also particularly susceptible to oil/water separator samples, with the daphnids frequently observed to be caught at the surface/water interface. These observations suggest that an accumulation of organic material at the air/water interface was responsible for the mortality ofD. magna. In subsequent tests, we also examined the relationship between theD. magna acute toxicity test and a bacterial-based assay (Toxi-Chromotest®) for several toxic effluents from Ontario Hydro stations to determine if bacterial-based tests could provide similar information in less time with smaller sample volumes. TheD. magma acute toxicity test did not correlate well with the bacterial-based Toxi-chromotest®. In particular, many of the samples which were toxic toD. magna were not toxic to the Toxi-chromotest® assay. The poor correlation between theD. magna and Toxi-chromotese® likely relates to both the relatively low toxicity of many of the effluent samples, and the fact that in many cases toxicity likely resulted from relatively simple combinations of inorganic toxicants. Accordingly, the Toxi-Chromotest® assay would not seem suitable as a surrogate for theD. magna acute toxicity test for our effluents.     

Characterization of Swine Wastewater by Toxicity Identification Evaluation Methodology (TIE)

Since swine wastewater is used by farmers for soil fertilization, evaluation of toxic compounds or micro-contaminants of separate streams is required. This paper uses the toxicity identification evaluation (TIE) procedure for the physicochemical and ecotoxicological characterization of swine wastewater. To distinguish the most important toxic compounds, a physicochemical characterization and phase I-TIE procedure were performed. The acute toxic effect of swine wastewater and treated fractions (phase II-TIE) were evaluated using Daphnia magna determining 48-h LC₅₀. Results show a high level of conductivity (23.5 μS cm⁻¹), which is explained as due to the concentration of ions, such as ammonium (NH₄⁺–N 1.6 g L⁻¹), sulfate (SO₄²⁻ 397.3 mg L⁻¹), and chlorine (Cl⁻ 1,230.0 mg L⁻¹). The acute toxicity of the swine wastewater was evaluated on D. magna (48-h LC₅₀ = 3.4%). Results of the different water treatments indicate that anionic exchange treatments could reduce 22.5% of swine wastewater’s acute toxicity by reducing chlorine (to around 51%) and conductivity (8.5%). On the other hand, cationic exchange treatment increased acute toxicity on D. magna (% RT = −624.4%), by reducing NH₄⁺–N (around 100%) and total nitrogen (95.5%). This finding suggests that part of the toxicity comes from anionic compounds, such as chlorine.     

Physiological Response of Daphnia magna to Linear Anionic Polyacrylamide: Ecological Implications for Receiving Waters

Linear anionic polyacrylamide (LA-PAM) is being considered as a soil amendment to reduce seepage and infiltration in unlined earthen canals. While polyacrylamides have been extensively used for potable water treatment, dewatering sewage sludge, coal and mine processing, paper manufacturing, and agriculture, little is known about its ecological impact to aquatic ecosystems. Acute toxicity (LC₅₀, 24 and 48 h) and chronic exposure tests (limited and continuous exposures) were conducted on Daphnia magna. In the chronic limited exposure experiments, Daphnia were exposed to LA-PAM for only 24 h whereas for the chronic continuous exposure the concentrations of 0, 0.5, 1, 5, 10, and 100 mg/L were tested and the endpoints of growth, onset to reproduction, fecundity, and mortality were measured for the duration of 32 days. There was no significant difference among the chronic, limitedly exposed organisms. The acute toxicity for LA-PAM was measured at 100, 150, 200, 250, and 300 mg/L. The acute test showed that the LC₅₀ for LA-PAM was at 152 mg/L. Overall in the chronic, continuous exposure test, D. magna was negatively impacted by LA-PAM at levels as low as 1 mg/L. Growth was reduced by 37% and 89% at 1 and 100 mg/L, respectively. Fecundity and onset to reproduction was impaired at 10 and 100 mg/L. Kinematic viscosity ranged from 0.98 cSt at 1 mg/L to 2.9 at 100 mg/L. At these levels, mechanical and physiological impairments due to the viscous properties of LA-PAM are the proposed mechanisms of reduction in the life history traits of D. magna.     

Acute toxicity of water soluble fractions derived from a coal liquid (SCR-II) to three aquatic organisms

Acute toxicity screening tests were conducted with water soluble fractions (WSFs) of a solvent refined coal (SRC-II) liquid from a pilot plant and three reference organisms: the cladoceran Daphnia magna, the fathead (FH) minnow Pimephales promelas, and larvae of the midge fly Chironomus tentans. Stock WSFs typically contained 900 to 1100 mg l^?1 total carbon (TC) and 700 to 800 mg l^?1 total dye complexable phenolics, with lower concentrations of aromatic and saturate hydrocarbons and N compounds. Under standard test conditions (temperature 20 °C, pH 7.3 to 8.2 and hardness 65 to 80 mg l^?1 CaCO₃), mean LC50 values in mg l^? TC were 3.3 for daphnia, 11.l for FH minnow, and 13.7 for midge larvae. Acute toxicity was also examined under other water quality conditions (temperature 10 or 25 °C, pH 6.0 or 6.5, and hardness ? 180 to 220 mg 1^?1 CaCO₃). The coal liquid was less toxic to daphnids at 10 °C than at 20 or 25 °C, but response of other organisms at different temperatures varied. The pH of the liquid had little effect on toxicity values. All organisms were less susceptible in hard water. Chemical compositions of stock WSFs were similar, suggesting that temperature, pH, and hardness had little effect on solubility of major synfucl components. Dilution indexes for stock WSFs were higher than for petroleum oils, and reflect the greater solubility of chemicals from the liquified coal in freshwater.     

Toxicity of Lead to Freshwater Invertebrates (Water fleas; Daphnia magna and Cyclop sp) in Fish Ponds in a Tropical Floodplain

Acute toxicity of Pb to the water flea; (Daphnia sp) and Copepod, (Cyclop sp) both important component of zooplankton diet of fish was determined by static assay. A positive relationship between percentage mortality and exposure concentration was found in all tests. Mean 24-h LC50, 48-h LC50 and 96-h LC50 values were 2.51?±?0.0.04 mg l^?1, 1.88?±?0.06 mg l^?1 and 1.65?±?0.19 mg l^?1 for Daphnia spp and 3.11?±?0.03 mg l^?1, 2.97?±?0.05 mg l^?1 and 2.61?±?0.09 mg l^?1 for Cyclop spp, respectively. For all tested species did the LC50 values decrease with time; the decrease was more marked for Daphnia spp. Observed symptoms include spiral movement followed by change of body colour to white and rapid disintegration of the skin. The Daphnia spp. appear to be more sensitive to Pb poison than Cyclop spp. The results showed that concentrations of Lead (Pb) in excess of 0.19 mg l^?1 and 0.30 mg l^?1 can be potentially harmful to Daphnia magna and Cyclop spp respectively.     

Toxicity of uranium to Daphnia magna

The toxicity of U to Daphnia magna was determined in acute and chronic tests. The 48-hr LC₅₀ of U (VI) in Columbia River water was 6 mg L^?1. Acute toxicity diminished by a factor of 7.5 as mean water hardness and alkalinity values increased from 70 mg L^?1. and 57 mg L^?1. to 195 mg L^?1. and 130 mg L^?1. respectively. This effect was most likely the result of complexation of uranyl ion with carbonate ions. D. magna reproduction was suppressed in Columbia River water at U concentrations between 0.5 and 3.5 mg L^?1. Potential hazards of U to aquatic life are discussed as they relate to mining practices.     

Preventive effects of amino acids on the toxicity of copper to Daphnia magna

The protective role of 18 amino acids on the acute toxicity of Cu in a fresh water cladoceran, Daphnia magna is reported. One hundred percent mortality in 48 hr of exposure occured at 0.56 mg L^?1 of Cu or higher. A dose of each tested amino acid (10 mg L^?1 was found to significantly neutralize the toxic effect of Cu as evidenced by a decrease in mortality and a significant increase in the median survival time (LT50) value). The 48 hr LC50 value was 0.093 mg L^?1 for Cu alone, while the LC50s with Cu plus amino acids ranged from 0.438 to 2.516 mg L^?1 of Cu, suggesting a 4.7 to 27 fold decrease in acute toxicity of Cu. A significant difference between LC50 of Cu alone and Cu with amino acids was observed. The role of amino acids for protection against heavy metal pollution stress in aquatic animals is discussed.     

Effect of Metals on Decolorization of Reactive Blue HERD by <Emphasis Type="Italic">Comamonas</Emphasis> sp. UVS

Comamonas sp. UVS was able to decolorize Reactive Blue HERD (RBHERD) dye (50 mg L^?1) within 6 h under static condition. The maximum dye concentration degraded was 1,200 mg L^?1 within 210 h. A numerical simulation with the model gives an optimal value of 35.71?±?0.696 mg dye g^?1 cell h^?1 for maximum rate (V_max) and 112.35?±?0.34 mg L^?1 for the Michaelis constant (K_m). Comamonas sp. UVS has capability of decolorization of RBHERD in the presence of Mg²⁺, Ca²⁺, Cd²⁺, and Zn²⁺, whereas decolorization was completely inhibited by Cu²⁺. Metal ions also affected the levels of biotransformation enzymes during decolorization of RBHERD. Comamonas sp. UVS was also able to decolorize textile effluent with significant reduction in COD. The biodegradation of RBHERD dye was monitored by UV–vis spectroscopy, FTIR spectroscopy, and HPLC.     

Toxicity of Sb and Cu in Sewage Sludge to Terrestrial Plants (Lettuce,Oat, Radish), and of Sludge Elutriate to Aquatic Organisms (Daphnia and Lemna) and its Interaction

Antimony (Sb) and Copper (Cu) are two metals of major concern in sewage sludge. Antimony because its use in society is increasing and this might lead to increased Sb concentrations in sludge. Copper because its total volume in use in society is large and because of corrosion from water pipes it is most difficult to reduce the Cu concentrations in sludge. Fresh digested sewage sludge was spiked with Cu or Sb and the sludge was cultivated with oat (Avena sativa), lettuce (Lactuca sativa) or radish (Raphanus sativus). Elutriates from the cultivated sludge were tested for toxicity with Lemna minor (7-d growth) and Daphnia magna (48 h immobility). Before cultivation the elutriates were toxic to Lemna and Daphnia due to high concentrations of ammonia (NH₃) and nitrite (NO₂ ^-). Cultivation decreased the concentrations of both NH₃ and NO₂ ^-, thereby reducing the impact of these compounds in the toxicity tests. Cultivation also decreased the metal concentrations and pH. Daphnia magna was the most sensitive test organism in this study with a 48 h EC₅₀ of 1130 mg Cu kg^-1 dry wt and 5 mg Sb kg^-1 dry wt in elutriates from sludge cultivated with oat. In sludge cultivated with radish the 48 h EC₅₀ was 1700 mg Cu kg^-1 dry wt and 22 mg Sb kg^-1 dry wt. The effect of Cu could be predicted by pH and Cu concentrationin the elutriate, but the effect of Sb could not solely be explained by its concentration in the elutriate.     

Evaluation of the Sub-lethal Toxicity of Bleached Kraft Pulp Mill Effluent to Carassius auratus and Dicentrarchus labrax

The effluents from bleached Kraft pulp mill (BKME) and paper industry are toxic to different aquatic organisms being an important source of contamination to aquatic environments due to the presence of several chemicals produced during the production of Kraft pulp. The main objective of the present study was to evaluate the exposure effects of a secondary-treated BKME in two different species of fish: Carassius auratus and Dicentrarchus labrax. Both species were exposed to different concentrations of secondary-treated effluent (1%, 10%, 25%, 50%, 100%) in semi-static tests under controlled laboratory conditions. At the end of the experimental period (21 days), samples of livers were collected for CYP1A determination and histopathological evaluation. The results show significant changes (p?<?0.05) of CYP1A induction in carp exposed to 50% and in sea bass exposed to 25% of the effluent. Histopathological alterations were also observed according to the different concentrations of the tested effluent suggesting that tested BKME cause damage to exposed organisms.     

Partial Nitritation-Anammox Granules: Short-Term Inhibitory Effects of Seven Metals on Anammox Activity

The inhibitory effect of seven different metals on the specific anammox activity of granular biomass, collected from a single stage partial nitritation/anammox reactor, was evaluated. The concentration of each metal that led to a 50% inhibition concentration (IC₅₀) was 19.3 mg Cu⁺²/L, 26.9 mg Cr⁺²/L, 45.6 mg Pb⁺²/L, 59.1 mg Zn⁺²/L, 69.2 mg Ni⁺²/L, 174.6 mg Cd⁺²/L, and 175.8 mg Mn⁺²/L. In experiments performed with granules mechanically disintegrated (flocculent-like sludge), the IC₅₀ for Cd⁺² corresponded to a concentration of 93.1 mg Cd⁺²/L. These results indicate that the granular structure might act as a physical barrier to protect anammox bacteria from toxics. Furthermore, the presence of an external layer of ammonia oxidizing bacteria seems to mitigate the inhibitory effect of the metals, as the values of IC₅₀ obtained in this study for anammox activity were higher than those previously reported for anammox granules. Additionally, the results obtained confirmed that copper is one of the most inhibitory metals for anammox activity and revealed that chromium, scarcely studied yet, has a similar potential inhibitory effect.     

TREATED EFFLUENT AND SALINE WATER IRRIGATION INFLUENCES SOIL PROPERTIES,YIELD, WATER PRODUCTIVITY AND SODIUM CONTENT OF SNOW PEAS AND CELERY

To determine the effects of irrigation water quality, plants were irrigated with normal potable water [0.25 dS m^?1 electrical conductivity (EC), 25 mg L^?1 sodium (Na), 55 mg L^?1 chloride (Cl)], treated effluent (0.94 dS m^?1 EC, 122 mg L^?1 Na, 143 mg L^?1 Cl) and saline water with low salinity (1.24 dS m^?1 EC, 144 mg L^?1 Na and 358 mg L^?1 Cl) and high salinity (2.19 dS m^?1 EC, 264 mg L ^?1Na and 662 mg L^?1 Cl) for snow peas, and high salinity (3.07 dS m^?1 EC, 383 mg L^?1 Na and 965 mg L^?1 Cl) and very high salinity (5.83 dS m^?1 EC, 741 mg L^?1 Na and 1876 mg L^?1 Cl) for celery. The greater salts build up in the soil and ion toxicity (Cl and Na) with saline water irrigation contributed to significantly greater reduction in root and shoot biomass, water use, yield and water productivity (yield kg kL^?1 of water used) of snow peas and celery compared with treated effluent and potable water irrigation. There was 8%, 56% and 74% reduction in celery yield respectively with treated effluent, high salinity and very high salinity saline water irrigation compared with potable water irrigation. The Na concentration in snow peas shoots increased by 54%, 234% and 501% with treated effluent, low and high salinity saline water irrigation. Similarly, the increases in Na concentration in celery shoots were 19%, 35% and 82%. The treated effluent irrigation also resulted in a significant increase in soil EC, nitrogen (N) and phosphorus (P) content compared with potable water irrigation. The heavy metals besides salts build up appears to have contributed to yield reductions with treated effluent irrigation. The study reveals strong implications for the use of saline water and treated effluent for irrigation of snow peas and celery. The salt build up within the root zone and soil environment would be critical in the long-run with the use of saline water and treated effluent for irrigation of crops. To minimize the salinity level in rhizosphere, an alternate irrigation of potable water with treated effluent or low salinity level water may be better option.     

Sediment Quality Assessment of Road Runoff Detention Systems in Sweden and the Potential Contribution of Tire Wear

Sediments from 18 different road runoff detention systems, located on the Swedish West Coast, were assessed for their ecological hazard potential. Thirteen of the sites were detention ponds, three were manholes within the same sedimentation construction, and two were detention basins handling wash water from road tunnels. Sediments from all sites were analysed for a range of physico-chemical parameters and contaminants, and screened for acute toxicity using Hyalella azteca (sediment), Daphnia magna (elutriate), and Ceriodaphnia dubia (elutriate) as the test organisms, and for chronic toxicity using C. dubia as the test organism. The benthic fauna of the thirteen detention ponds was also studied. Sediment quality guidelines probable effect levels were exceeded for one or several contaminants at half of the sites, and one third revealed toxicity in some of the bioassays. Most of the detention ponds were dominated by tolerant taxa indicating low biological quality. Relationships between contaminant concentrations, toxicity in bioassays, and benthic fauna were, however, found to be weak. Extractable organic Zn, which was used as a tire wear marker, correlated with Zn, Cu, presumably from brake linings, and W, a common component of tire studs. The highest concentration, which was found in the manholes (14 mg kg^?1 ds), corresponds to a tire wear concentration of 11 g kg^?1 ds. The results of the present study have shown that traffic related contaminants accumulate in the studied runoff treatment systems, and, therefore, the maintenance of them is crucial in order to prevent contamination of surrounding waters.     

Microfauna Community as an Indicator of Effluent Quality and Operational Parameters in an Activated Sludge System for Treating Piggery Wastewater

In order to study the potential use of microfauna as an indicator of effluent quality and operational parameters in an activated sludge system for treating piggery wastewater, an experimental sequencing batch reactor was set up and evaluated by biological and physical–chemical analyses for 12 months. Results show that microfauna (and specifically ciliate protozoa) are a good parameter for assessing effluent quality in terms of both chemical oxygen demand (COD) and ammonia and for assessing the organic and nitrogen load of the system. Specifically, the abundance of ciliates decreases from 20,000 individuals·mL^?1 to ca. 2,500 individuals·mL^?1 and from ca. 10,000 individuals mL^?1 to ca. 200 individuals mL^?1 when effluent concentration is between 550 and 750 mg L^?1 and above 100 mg L^?1 to the COD and ammonia concentrations, respectively. Furthermore, microfauna abundance is reduced from ca. 18,000 individuals mL^?1 (organic load between 0.1 and 0.2 mg COD mg total suspended solids (TSS)^?1 day^?1) to ca. 500 individuals mL^?1 (organic load between 0.3 and 04 mg COD mg TSS^?1 day^?1). Microfauna abundance also decreases as nitrogen loading increases. Nitrogen loading in the range of 5–60 mg NH₄–N g TSS^?1 day^?1 does not have any significant effect on microfauna abundance. However, ammonia loading from 60 to 120 mg NH₄–N g TSS^?1 day^?1 reduces microfauna abundance ca. 6-fold. Ciliate protozoa were the largest microfauna group during the whole period of study, representing ca. 75% of the total microfauna abundance. The largest group in the ciliate community was that of the free-swimming ciliates. This was followed by the group of attached and crawling ciliates. Specifically, the dominant ciliate species during the whole study period were Uronema nigricans, Vorticella microstoma-complex, Epistylis coronata, and Acineria uncinata.     

Individual and additive effects of Na+ and Cl− ions on rice under salinity stress

This study was attempted to assess the extent of toxicity contributed by Na⁺ and/or Cl^? ions individually, besides their possible additive effects under NaCl using physiological and biochemical parameters. Despite the fact that most annual plants accumulate both Na⁺ and Cl^? under saline conditions and each ion deserves equal considerations, most research has been focused on Na⁺ toxicity. Consequently, Cl^? toxicity mechanisms including its accumulation/exclusion in plants are poorly understood. To address these issues, effects of equimolar (100 mM) concentrations of Na⁺, Cl^? and NaCl (EC ≈ 10 dS m^?1) were studied on 15-day-old seedlings of two rice cultivars, Panvel-3 (tolerant) and Sahyadri-3 (sensitive), using in vitro cultures. All three treatments induced substantial reductions in germination rate and plant growth with greater impacts under NaCl than Na⁺ and Cl^? separately. Apparently, salt tolerance of Panvel-3 was due to its ability to exclude Na⁺ and Cl^? from its shoots and maintaining low (<1.0) Na⁺/K⁺ ratios. Panvel-3 exhibited better vigour and membrane stability indices coupled with lower reactive oxygen species and lipid peroxidation levels, besides stimulated synthesis of proline, glycine betaine and ascorbic acid. Overall, the magnitude of toxicity was observed in NaCl > Na⁺ > Cl^? manner. Though Cl^? was relatively less toxic than its countercation, its effect cannot be totally diminished.     

The Efficacy of a Tropical Constructed Wetland for Treating Wastewater During the Dry Season: The Kenyan Experience

Constructed wetlands have recently received considerable attention as low cost and efficient means of cleaning up many different types of wastewaters at secondary and tertiary levels. This is an environmentally sound method of wastewater treatment that does not use hazardous chemicals, and is based on the high productivity and nutrient removal capability of the wetland that strongly relies on its intricate ecosystem structure and function. Research work was conducted on a tropical constructed wetland to establish its capability to treat wastewater during the dry season. A comparison of its efficacy with that of conventional wastewater treatment plants was made on the basis of the measured water quality parameters. Temperature, pH, dissolved oxygen, and conductivity were measured in situ. Total suspended solids (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), phosphorus, ammonia, and nitrites were analyzed in the laboratory. Fecal coliforms were enumerated and Escherichia coli counts were determined. The TSS values reduced from a mean of 102 mg/l at the influent point to 16 mg/l at the effluent point, depicting a reduction of 84.3%. Influent TDS averaged 847 mg/l, while the effluent averaged 783 mg/l. Dry season BOD₅ levels were reduced from an average of 286 at the inlet point to 11 mg/l at the outlet representing a reduction efficiency of 96.2%. COD levels were reduced from a mean of 2,002.5 to 47.5 mg/l depicting a removal efficiency of 97.6%. Phosphorus was reduced from a mean of 14 to 11 mg/l representing a percentage removal of 21.4%. Levels of ammonia reduced from a mean of 61 at the influent point to 36 mg/l at the effluent point representing a percent reduction of 41.0%. There was a 99.99% reduction for both the fecal coliforms and E. coli counts. Conductivity of wastewater increased from 1.08 to 1.98 mS, while the pH increased from 6.23 at the inlet point to 7.99 at the outlet of the system. Temperature and dissolved oxygen measurements showed a diurnal variation. The dry season wastewater heavy metal concentrations were in the following ranges: Pb (0.7?C6.9 ppm), Cr (0.2?C0.5 ppm), Zn (0.1?C2.3 ppm), Ni (0.1?C1.3 ppm) with Cd and Cu not being detected in the wastewater streams. Overall, tropical constructed wetlands are effective in treating wastewater streams and they perform a lot better than the popularly used waste stabilization ponds. This paper recommends that they can be widely used within the tropics.     

Toxicity reduction of Ontario hydro radioactive liquid waste

The radioactive liquid waste (RLW) system in Ontario Hydro's pressurised heavy water reactors collects drainage from a variety of sources ranging from floor drains to laundry waste. RLW effluent was intermittently toxic to rainbow trout andDaphnia magna during the first phase of Ontario's Municipal Industrial Strategy for Abatement (MISA) Program, apparently as a result of the interaction of a variety of known and unknown organic and inorganic compounds. Accordingly, we employed a tmatment-based approach to reducing its toxicity, supplemented by chemical analysis. Two series of toxicity reduction tests were conducted. The fast series explored the potential for sorption of the possible toxicants, while the accord series incorporated a wider variety of treatments. Of the 24 samples in the first test series, 17 were toxic (D. magna mortality ≥ 50%). Of the toxic samples, only 7 of 17 were still toxic after passage through an activated carbon column, but 5 of 6 samples tested remained toxic after passage through a metal chelating resin column. In the second series, at least one of the treatments was effective in reducing toxicity of all samples which were initially toxic (16 of 24 samples), but no one treatment was effective for all toxic samples. Three treatments (UV/H₂O₂ photo-oxidation with prior pH adjustment, or passage through a column of either a non-functioalized (N-F) resin or a mixture of N-F resin and a weak base (W-B) anion exchange rain), were effective in reducing the toxicity of more than 50% of the toxic samples; yet roughly 25% of these samples remained toxic after treatment O₂ sparging, UV/H₂O₂ photo-oxidation without prior pH adjustment, and passage through a column of the W-B Resin were less effective, as more than 50% of the samples remained toxic after treatment. Filtering was not effective, as all of the treated samples (9/9) retained their toxicity. There was no obvious correspondence between toxicity and the concentrations of metals (Cu, Zn, Fe, Al and Cd) nor were any simple relationships apparent between toxicity and Total Organic Carbon or NH₃ concentrations. At stations where radioactive liquid wastes are segregated, toxicity was also segregated, suggesting that we may be able to address the problem at source through a combination of Best Management Practices and smaller scale treatment facilities.     

Removal of Cyanide and Zinc–Cyanide Complex by an Ion-Exchange Process

Removal efficiencies of cyanide and a zinc–cyanide complex in solutions were studied by using an ion-exchange process at pH 10.0 and 12.0. An anion-exchange resin, AMBERLITE® IRA-402 Cl, was used to perform packed bed continuous experiments. For the initial 200 mg/l cyanide solution, the packed bed gave a cyanide effluent concentration of 0.2 mg/l at 80 bed volumes for both pH 10.0 and 12.0. Comparatively, in the mixture of 200 mg/l cyanide and 100 mg/l zinc, packed bed volumes were obtained as 80 and 90 at pH 10.0 and 12.0, respectively, to have 0.2 mg/l cyanide effluent concentrations. The packed beds were exhausted at 250 and 400 bed volumes for cyanide and zinc–cyanide complex solutions, respectively. Speciation calculations in Zn(II)/cyanide/OH^? were used to interpret the results. The exchange capacities of the resin were determined as ～1.2 and ～0.9 meq/ml resin for cyanide and zinc–cyanide complex solutions, respectively, and were independent of pH in the studied pH range.     

The Transport of Escherichia coli Through Freeze-Fractured Clay Soil

Little is known about the transport of microorganisms through freeze-fractured clay soils. Normally consolidated clay (NCC) and compacted clay (CC) columns (representing a natural clay barrier and a compacted barrier, respectively) were exposed to six consecutive freeze–thaw cycles and permeated for 21 days with an Escherichia coli cell suspension (approximately 1?×?10⁷ colony forming units (CFU)/mL) containing a 2.1-mM bromide tracer. An unfractured sand column was also examined for comparison with the clay columns. While no E. coli was detected in the effluent of both untreated NCC and CC control clay columns, a relatively low density of E. coli (between 228 and 270 CFU/mL compared to 1?×?10⁷ CFU/mL in the influent) was first detected in the effluent of the freeze-fractured NCC and CC columns at 0.29 and 0.31 pore volumes (or at 5.4 and 4.1 h), respectively. It took 11 min for a full breakthrough of E. coli through the sand column, but only about 0.1% of the influent E. coli density was detected in the effluents of the freeze-fractured NCC and CC columns at day 21. These observations show that despite the high bacterial retention capacity of the freeze-fractured clay columns, the fractures were large enough for the E. coli to flow through. Based on batch sorption tests and the permeation data, it is estimated that 18%, 7%, and 84% of the freeze-fractured NCC, CC, and sand columns would be exposed to the influent, respectively, under a full E. coli breakthrough condition. Our data show that the high bacterial retention capacity of clay barriers can be compromised by freeze–thaw conditions.