Over a century of metal processing activity has resulted in widespread metal contamination of soils in Sudbury, ON, Canada. To assess the potential for recovery from the large reductions in metal deposition, critical loads were estimated for metals at 415 sites in Sudbury using an ‘effects based’ approach that is based on exceedance of provincial soil guidelines using multiple independent estimates of metal partitioning (Kd) for each metal. Sudbury soils are heavily contaminated with copper (Cu) and nickel (Ni), with 74 % of samples currently exceeding the provincial soil guideline for Cu and 87 % of samples exceeding the guideline for Ni. Both metals are strongly correlated with other metals (zinc (Zn), cadmium (Cd), lead (Pb)), although they rarely exceed provincial guidelines Copper and Ni are also strongly correlated with organic matter but not soil pH. Based on the most recent Cu and Ni deposition estimates (mid-1990s), it is estimated that between 20 % and 51 % of the sites receive deposition in excess of the ‘effects based’ critical load for Cu and between 5 % and 97 % of sites receive atmospheric deposition in excess of the ‘effects based’ critical load for Ni. These results suggest that Cu and Ni concentrations in soil will generally decrease resulting in slightly fewer sites that exceed the provincial soil guideline, but that the timeframe of this response will be very slow, with relatively little change occurring over the next 100 years. Even assuming a best case deposition scenario whereby Cu and Ni deposition were to immediately fall to background levels, the percentage of sites with Cu and Ni levels in excess of the OMOE guideline would still be between 69 % and 72 %, and 56 % and 86 %, respectively, demonstrating that while recovery of the Sudbury soils is possible, greater reductions in metal deposition are needed and even so, it will be a process that takes several centuries.

Contact time, pH, fluoride concentration, and sorbent dose effects on the removal of fluoride ions by a carbonaceous material obtained from pyrolysis of sewage sludge (CM) were evaluated. Equilibrium was reached after 18 h of contact time and the maximum sorption was found at pHeq = 7.06 ± 0.08, which corresponds to the zero charge point of the CM. The highest efficiency in the sorption system for fluoride removal (2.84 ± 0.03 mg F− [Formula: see text]) was found with 0.4 gCM L−1 and with 20 gCM L−1, 82.2 ± 0.5% of fluoride was removed. The kinetic data of the process could be fitted to the pseudosecond order and the intraparticle mass transfer diffusion models, whereas isotherm to the Langmuir–Freundlich equation. These results indicate that the mechanism is chemisorption on a heterogeneous material. Fluoride ions were best partially desorbed using a bicarbonate ions solution and the material was partially regenerated by using a solution of HCl (pH = 1).

Low impact development (LID) is a land development strategy for managing stormwater at the source with decentralized micro-scale control measures. Since the emergence of LID practices, they have been successfully used to manage stormwater runoff, improve water quality, and protect the environment. However, discussions still surround the effectiveness of many of these practices, resulting in a reluctance to widely adopt them. This paper highlights evidence in the literature regarding the beneficial uses of LID practices. A discussion of how LID practices are represented in hydrologic/water quality models is also provided using illustrative examples of three computational models developed with algorithms and modules to support widespread adoption of LID practices. Finally, the paper suggests directions for future research opportunities.

Polybrominated diphenyl ethers (PBDEs) are highly persistent anthropogenic contaminants found in trace amounts in many environmental compartments far from their source areas, posing a risk to aquatic ecosystems. Our objective was to determine the relative toxicities of three BDEs, BDE-47, BDE-99 and BDE-154 on marine phytoplankton algae Isochrysis galbana. For a highly sensitive endpoint: the 72-h inhibition of autotrophic growth rate was calculated according to standards methods. Actual PBDE concentration was measured by GC-MS and toxicity parameters were calculated on the basis of time-weighted mean actual concentrations. No observable effect concentration (NOEC) values were 2.53 μg L⁻¹ for BDE-47, 3.48 μg L⁻¹ for BDE-99 and 12.3 μg L⁻¹ for BDE-154, and LOEC values were 5.06, 6.96 and 24.60 μg L⁻¹ for BDE-47, BDE-99 and BDE-154, respectively. The calculated IC₁₀ (the concentration inhibiting growth rate by 10 %) corresponded to 9.3, 12.78 and 54.6 μg L⁻¹ for BDE-47, BDE-99 and BDE-154, respectively. The 50 % inhibitions of growth rate (IC₅₀) values were: 25.7 μg L⁻¹ BDE-47, 30.0 μg L⁻¹ BDE-99 and 243.7 μg L⁻¹ BDE-154. Therefore, the acute toxicity of PBDEs decreases as the degree of bromination increases, the order of toxicity is BDE-47 > BDE-99 > BDE-154. Significant (p < 0.05) adverse effects were observed for all compounds at concentrations >15 μg L⁻¹. Our results indicated that under laboratory conditions PBDEs inhibited the growth of marine phytoplankton at concentrations near 10 μg L⁻¹. However, further work is required to investigate long-term effects in these and other aquatic organisms.

In domestic wastewater, bacterial physiology controls cell production (growth, replication) and cell maintenance, determining how energy is allocated between these two processes. The aim here was to develop a method to quantify these cellular processes so that the bacterial physiological state could be manipulated to lower this source of pollution. We simultaneously used the incorporation of radiolabelled thymidine into DNA (a measure of new cell synthesis) and leucine into protein in wastewater to quantitatively distinguish bacterial growth from maintenance processes. We found that DNA and protein syntheses were coupled in wastewater after substrate enrichment (with glucose or acetate)—balanced growth. Once the substrate was depleted, the two processes became uncoupled—unbalanced growth. In this physiological state, the bacteria were synthesising protein, but fewer bacteria were replicating. More energy was allocated to cell maintenance than replication. A mean Leu/TdR ratio of 7.4 was determined for wastewater and was similar to natural aquatic ecosystems. As the bacterial growth rate decreased, the Leu/TdR ratios increased. We show how the simultaneous measurement of [³H]Leu and [³H]TdR quantitatively distinguishes balanced from unbalanced growth. Low [³H]Leu/[³H]TdR ratios indicated bacteria were physiologically stressed, an ideal state for biological wastewater treatment processes (WWTP) as the bacteria divert more energy to maintenance activities instead of growth. Leu/TdR ratios of 70 have been recorded in natural aquatic ecosystems which suggests WWTP have potential to be manipulated to achieve much higher Leu/TdR ratios than we report here. Changes to plant operation to improve operation efficiency include finding the optimum rate of substrate (pollution supply) or alternating aerobic and anaerobic periods to maximise the Leu/TdR ratio to achieve less biomass production for land disposal and more cost-effective operation that generates less pollution in the effluent.

We examined the effects of an amended mixture of three pesticides, atrazine (72.7 g), S-metolachlor (54.5 g), and permethrin (both cis and trans isomers; 11.4 g), on 10-day sediment toxicity to Hyalella azteca in a managed natural backwater wetland after a simulated agricultural runoff event. Sediment samples were collected at 10, 40, 100, 300, and 500 m from inflow 13 days prior to amendment and 1, 5, 12, 22, and 36 days post-amendment. Background pesticide concentrations ranged from <1 to 977, <1 to 119, and <1 to 2 μg kg⁻¹, for atrazine, S-metolachlor, and permethrin, respectively. Average post-amendment atrazine and S-metolachlor were 2,915–3,927 and 3–20 μg kg⁻¹, respectively at 10–40 m and 538–872 and <1 μg kg⁻¹, respectively at 300–500 m. Average post-amendment permethrin was 65–200 μg kg⁻¹ at 10–40 m and 1–10 μg kg⁻¹ at 300–500 m. H. azteca 10-day survival varied spatially and temporally up to 100 m from inflow. Animal growth, independent of survival, was reduced 40 and 100 m from inflow on day 36, showing continued sediment toxicity of up to 100 m from inflow more than 1 month after amendment. Animal survival and growth were unaffected at 300 and 500 m from inflow throughout the study period. Correlations of pesticide concentrations and H. azteca responses indicated that observed sediment toxicity was primarily from permethrin with potential additional synergistic toxicity from atrazine and methyl parathion. Study results indicate that natural backwater wetlands can be managed to ameliorate pesticide mixture 10-day sediment toxicity to H. azteca within 300 m of inflow and smaller wetlands (≤100 m) may require several months of effluent retention to mitigate effects.

A thin film of well-ordered anatase TiO₂ nanotubes prepared by anodic oxidation of titanium metal were synthesised and used as adsorbent medium for the purification of water from aqueous uranium and lead. The amount of subtracted metal ions was quantified by using X-ray photoelectron spectroscopy at the surface of the reacted TiO₂ surface. Batch experiments for the sorption of U and Pb at the surface of the titania substrate were carried out in separated solution equilibrated with air of uranyl acetate and lead nitrate, in the pH range 3–9. For uranium, the experiments were also repeated in anoxic (N₂) atmosphere. The amount of metal ions adsorbed onto the titania medium was quantified by measurements of the surface coverage expressed in atomic percent, by recording high-resolution XPS spectra in the Ti2p, U4f and Pb4f photoelectron regions. Adsorption of the uranyl species in air atmosphere as a function of pH showed an adsorption edge near pH 4 with a maximum at pH 7. At higher pH the presence of very stable uranyl–carbonate complexes prevented any further adsorption. Further adsorption increased until pH 8.5 was obtained when the uranyl solution was purged from dissolved CO₂. Lead ion showed a sorption edge at pH 6, with a maximum uptake at pH 8. The results showed that the uptake of uranium and lead on the selected titania medium is remarkably sensitive to the solution pH. This study demonstrates the reliability of this type of material for treating water polluted with heavy metals as well as leachates from radioactive nuclear wastes.

Perchlorate (ClO 4 − ), a thyroid hormone disruptor, is both naturally occurring and a man-made contaminant increasingly found in a variety of terrestrial environments. The environmental presence of ClO 4 − is considered to be the result of atmospheric formation and deposition processes. The ultimate processes, particularly heterogeneous-based reactions, leading to natural ClO 4 − formation are not well understood. Oxidation of chlorine species by an energetic source such as lightning is considered to be one of the potential heterogeneous sources of natural ClO 4 − . Currently, there is very little information available on lightning-induced ClO 4 − . We designed a laboratory electrical discharge reactor capable of evaluating ClO 4 − formation by the oxidation of “dry” sodium chloride (NaCl) aerosols (relative humidity (RH) <70%) in electrical discharge plasma at voltages and energies up to 24 kV and 21 kJ, respectively. Similar to other non-electrochemical ClO 4 − production processes, the amount of ClO 4 − produced (0.5–4.8 μg) was 3 orders of magnitude lower than the input Cl− (7.1–60.1 mg). The amount of ClO 4 − generated increased with peak voltage (V) and theoretical maximum discharge energy with ΔClO 4 − /ΔV = 0.28 × 10−3 μg V−1 (R 2 = 0.94) and ΔClO 4 − /ΔE = 0.44 × 10−3 μg J−1 (R 2 = 0.83). The total ClO 4 − generated decreased with an increase in relative humidity from 2.8 ± 0.1 μg (RH ∼46%) to 0.9 ± 0.1 μg (RH ∼62%) indicating that the presence of moisture inhibits the formation of ClO 4 − . Additional modifications to the reactor support the hypothesis of ClO 4 − formation due to the action of plasma on Cl− aerosols as opposed to direct oxidation on the surface of the electrodes. Finally, the contribution of lightning-induced ClO 4 − in North America is calculated to have a wide range from 0.006 × 105 to 5 × 105 kg/year and is within the range of the measured ClO 4 − depositional flux in precipitation samples obtained across the USA (0.09 × 105–1.2 × 105 kg/y).

Groundwater and surface water contamination have been linked to inadequate or failing on-site residential wastewater treatment and disposal systems. The potential for groundwater contamination in coastal areas with shallow water tables is higher; subsequently the ability of soil, microorganisms, and vegetation to mitigate pollutants may be reduced. This study evaluated the performance of the four types of on-site wastewater treatment and disposal systems predominantly used on the Mississippi Gulf Coast. One type of system was deemed inappropriate for this region as none of the dozens of installations examined were functioning acceptably. Of the remaining three types, subsurface water samples were collected from representative sites using lysimeters and monitoring wells. Apart from general performance evaluation of these systems, seasonal changes translating into possible variation in disposal efficiencies and groundwater contamination were investigated. Statistical analysis of variations in organics (COD and BOD₅), nitrogen (TKN and NH ₄ ⁺ –N), and fecal coliform concentrations was used to identify probable deficiencies in systems tested and to recommend changes to governing standards.

The adsorption of methylene blue cationic dye by water hyacinth root was studied in a batch system. The experimental data isotherms were analyzed using the Langmuir and Freundlich equations. The monolayer adsorption capacity for methylene blue dye was found as 0.187 kg kg−1. Three kinetic models (the pseudo-first order, the pseudo-second order, and the unified approach) were used to calculate the adsorption rate constants. The kinetic data along with equilibrium constants (maximum monolayer capacity and Langmuir constant) fitted well with unified approach model for different initial concentrations, and the rate constants were determined. Laboratory column experiments were conducted to evaluate the performance of water hyacinth root for methylene blue sorption under dynamic flow conditions. Breakthrough curves were plotted for the methylene blue adsorption on the adsorbent using continuous flow column operation by varying the bed height (0.06–0.12 m) and the feed concentrations (0.1–0.2 kg m−3). Different column design parameters, such as depth of exchange zone, adsorption rate, and adsorption capacity, were calculated. At the end, an attempt has also been made to model the data generated from column studies using the empirical relationship based on Bohart–Adams model.