Drew C. McAvoy

MINEQL+ : a software environment for chemical equilibrium modeling

Abstract Water quality issues are essential to environmental policy at all levels of government. In order to better understand the chemistry of aquatic systems, computational models have been developed that calculate the chemical equilibrium (CE) behavior of chemical constituents in solution. These models have considerable potential as tools in studying groundwater geochemistry, aquatic toxicology, or water and waste water engineering. Although numerically advanced, these models are typically poor with respect to human interaction and data management issues. In this paper, the process of CE modeling is examined within the context of developing data management and modeling environment software. We explore the issues of software extendibility and modularization, user interface, dynamic editing, and data management as a means of developing software that allows better use and learning of CE modeling. MINEQL+ is a CE modeling environment that employs these software qualities. As an integrated environment, MINEQL+ represents a new direction in CE research by building on a solid numerical structure while emphasizing ease of model use.

Measurement of alkyl ethoxylate surfactants in natural waters

Alkyl ethoxylate alcohols (AE) are used in a wide variety of household cleaning products. In order to monitor environmental levels of AE and to determine AE removal during wastewater treatment, an analytical procedure that provides total AE concentration resolved by alkyl chain length for various environmental matrices (influent, effluent, and river water) was developed. The method utilizes a reverse-phase column to extract and concentrate AE from surface waters and wastewaters and utilizes strong anionic and cationic exchange columns to remove potential interferences. AE were reacted with hydrogen bromide to form corresponding alkyl bromide derivatives that were analyzed by capillary gas chromatography with mass selective detection. Recovery of AE from influent, treatment plant effluent, and river water was quantitative (65-102%) over a range of concentrations for all matrices. AE removal was 99% at two activated sludge treatment plants and 92% at two trickling filter plants. Total AE in low dilution (effluent to river water) surface waters downstream from wastewater treatment plants were less than 0.037 mg/L.

The influence of untreated wastewater to aquatic communities in the Balatuin River, The Philippines.

A risk assessment of chemical constituents in rivers that receive untreated wastewater should take into account the adverse effects of increased biological oxygen demand (BOD), ammonia and reduced dissolved oxygen (DO). This concept was tested via a field study in the Balatuin River, The Philippines, where the influence of physical and chemical factors, including the consumer product chemical linear alkylbenezene sulfonate (LAS), to aquatic communities (algae, invertebrates, fish) was determined. Periphytic algae were found to be insensitive to high BOD (>10 mg/l) and ammonia (>0.01 mg unionized NH(3)/l), concentrations from organically enriched untreated wastewater discharges. However, taxa richness and abundance of macroinvertebrates were influenced greatly by the discharges. Where BOD and ammonia concentrations were elevated, the dominant taxa were oligochaete worms and chironominds. Fish and crustaceans (freshwater crabs and prawns) were found only in sites with the least BOD concentrations (furthest upstream and downstream). The maximum concentration of LAS (0.122 mg/l) was less than that expected to affect 5% of taxa (0.245 mg/l), whereas exceedences of DO and ammonia criteria were observed in several sites. The lack of recovery observed was attributed to influences of low DO, high ammonia and poor colonization from upstream and downstream reaches due to organically-enriched discharges

Toxicity and bioaccumulation of biosolids-borne triclocarban (TCC) in terrestrial organisms

Triclocarban (TCC) toxicity and bioaccumulation data are primarily limited to direct human and animal dermal exposures, animal ingestion exposures to neat and feed-spiked TCC, and/or aquatic organism exposures. Three non-human, terrestrial organism groups anticipated to be the most highly exposed to land-applied, biosolids-borne TCC are soil microbes, earthworms, and plants. The three ecological receptors are expected to be at particular risk due to unique modes of exposure (e.g. constant, direct contact with soil; uptake of amended soil and pore water), inherently greater sensitivity to environmental contaminants (e.g. increased body burdens, permeable membranes), and susceptibility to minute changes in the soil environment. The toxicities of biosolids-borne TCC to Eisenia fetida earthworms and soil microbial communities were characterized using adaptations of the USEPA Office of Prevention, Pesticides, and Toxic Substances (OPPTS) Guidelines 850.6200 (Earthworm Subchronic Toxicity Test) and 850.5100 (Soil Microbial Community Toxicity Test), respectively. The resultant calculated TCC LC50 value for E. fetida was 40 mg TCC kg amended fine sand(-1). Biosolids-borne TCC in an amended fine sand had no significant effect on soil microbial community respiration, ammonification, or nitrification. Bioaccumulation of biosolids-borne TCC by E. fetida and Paspulum notatum was measured to characterize potential biosolids-borne TCC movement through the food chain. Dry-weight TCC bioaccumulation factor (BAF) values in E. fetida and P. notatum ranged from 5.2-18 and 0.00041-0.007 (gsoil gtissue(-1)), respectively.

Risk assessment approach for untreated wastewater using the QUAL2E water quality model

This paper presents a novel approach for assessing the risk of consumer product ingredients in surface waters that receive untreated wastewater. The approach utilizes the water quality simulation model QUAL2E for predicting the impact caused by conventional pollutants, as well as the exposure concentration of consumer product ingredients. This approach invokes an impact zone concept whereby the receiving water can be thought of as a natural wastewater treatment system. After the river has recovered via self-purification, the ecosystem is then assessed by traditional risk assessment methods. This approach was validated using data collected from the Balatuin River, which is located in the Philippines. Results from this study support the use of QUAL2E for assessing the risk of consumer product ingredients in riverine systems receiving untreated wastewater.

Environmental Safety of the Use of Major Surfactant Classes in North America

This paper brings together over 250 published and unpublished studies on the environmental properties, fate, and toxicity of the four major, high-volume surfactant classes and relevant feedstocks. The surfactants and feedstocks covered include alcohol sulfate or alcohol sulfate (AS), alcohol ethoxysulfate (AES), linear alkylbenzene sulfonate (LAS), alcohol ethoxylate (AE), and long-chain alcohol (LCOH). These chemicals are used in a wide range of personal care and cleaning products. To date, this is the most comprehensive report on these substances chemical structures, use, and volume information, physical/chemical properties, environmental fate properties such as biodegradation and sorption, monitoring studies through sewers, wastewater treatment plants and eventual release to the environment, aquatic and sediment toxicity, and bioaccumulation information. These data are used to illustrate the process for conducting both prospective and retrospective risk assessments for large-volume chemicals and categories of chemicals with wide dispersive use. Prospective risk assessments of AS, AES, AE, LAS, and LCOH demonstrate that these substances, although used in very high volume and widely released to the aquatic environment, have no adverse impact on the aquatic or sediment environments at current levels of use. The retrospective risk assessments of these same substances have clearly demonstrated that the conclusions of the prospective risk assessments are valid and confirm that these substances do not pose a risk to the aquatic or sediment environments. This paper also highlights the many years of research that the surfactant and cleaning products industry has supported, as part of their environmental sustainability commitment, to improve environmental tools, approaches, and develop innovative methods appropriate to address environmental properties of personal care and cleaning product chemicals, many of which have become approved international standard methods.

Advanced steady-state model for the fate of hydrophobic and volatile compounds in activated sludge

A steady-state, advanced, general fate model developed to study the fate of organic compounds in primary and activated-sludge systems. This model considers adsorption, biodegradation from the dissolved and adsorbed phases, bubble volatilization, and surface volatilization as removal mechanisms. A series of modeling experiments was performed to identify the key trends of these removal mechanisms for compounds with a range of molecular properties. With typical municipal wastewater treatment conditions, the results from the modeling experiments show that co-metabolic and primary utilization mechanisms give very different trends in biodegradation for the compounds tested. For co-metabolism, the effluent concentration increases when the influent concentration increases, while the effluent concentration remains unchanged when primary utilization occurs. For a highly hydrophobic compound, the fraction of compound removed from adsorption onto primary sludge can be very important, and the direct biodegradation of compound sorbed to the activated sludge greatly increases its biodegradation and reduces its discharge with the waste activated sludge. Volatilization from the surface of the primary and secondary systems is important for compounds with moderate to high volatilities, especially when these compounds are not biodegradable. Finally, bubble volatilization can be a major removal mechanism for highly volatile compounds even when they are highly biodegradable.

Effects of nutrient trace metal speciation on algal growth in the presence of the chelator [S,S]-EDDS

This study tests the hypothesis that the apparent toxicity of strong chelators in standard algal growth inhibition tests (e.g. method OECD 201, EC C.3., ISO 8692) is related to essential trace metal bioavailability. This hypothesis was investigated for the chelator [S,S]-ethylene diamine disuccinate ([S,S]-EDDS) and the green alga Chlorella vulgaris. Metal speciation calculations were used to help design the algal growth experiments and interpret the data. Results suggest that interaction of the chelator with trace metals alters the free metal concentration and affects algal population growth, as opposed to a direct interaction between the alga and the chelator (toxicity sensu stricto). Even low levels of [S,S]-EDDS (i.e. 3 mg l-1 or less) reduce the free p(Cu) and p(Zn) (p(Metal) = -log[Metal]) in standard OECD medium below 16 and 11, respectively, which are the minimum levels required to support algal growth. Nutrient deficiency was overcome by supplementing the medium with appropriate amounts of the trace metals Cu, Zn and Co, but not by increasing the hardness of the medium. A short-term photosynthesis inhibition experiment with the alga Selenastrum capricornutum in metal-free medium showed only a minimal effect of[S,S]-EDDS on the 14C-CO2 fixation rate. About 10% inhibition was observed at 100 mg [S,S]-EDDS l-1, i.e. the EC50 for CO2 fixation is greater than 100 mg l-1. Results from this study illustrate that the standard algal growth inhibition test is not well suited to the assessment of algal toxicity (sensu stricto) of strong chelators. The no-effect level and EC50 value are probably overestimated by at least one order of magnitude for [S,S]-EDDS. The study also illustrates the importance of speciation calculations when assessing algal inhibition by chelators.

Fate of 14C–triclocarban in biosolids-amended soils

Triclocarban (TCC) is an antibacterial compound commonly detected in biosolids at parts-per-million concentrations. Approximately half of the biosolids produced in the United States are land-applied, resulting in a systematic release of TCC into the soil environment. The extent of biosolids-borne TCC environmental transport and potential human/ecological exposures will be greatly affected by its bioavailability and the rate of degradation in amended soils. To investigate these factors, radiolabeled TCC ((14)C-TCC) was incorporated into anaerobically digested biosolids, amended to two soils, and incubated under aerobic conditions. The evolution of (14)CO2 (biodegradation) and changes in chemical extractability (bioavailability) was measured over time. Water extractable TCC over the study period was low and significantly decreased over the first 3 weeks of the study (from 14% to 4% in a fine sand soil and from 3 to <1% in a silty clay loam soil). Mineralization (i.e. ultimate degradation), as measured by evolution of (14)CO(2), was <4% over 7.5 months. Methanol extracts of the amended soils were analyzed by radiolabel thin-layer chromatography (RAD-TLC), but no intermediate degradation products were detected. Approximately 20% and 50% of the radioactivity in the amended fine sand and silty clay loam soils, respectively, was converted to bound residue as measured by solids combustion. These results indicate that biosolids-borne TCC becomes less bioavailable over time and biodegrades at a very slow rate.

Measured physicochemical characteristics and biosolids-borne concentrations of the antimicrobial Triclocarban (TCC)

Triclocarban (TCC) is an active ingredient in antibacterial bar soaps, a common constituent of domestic wastewater, and the subject of recent criticism by consumer advocate groups and academic researchers alike. Activated sludge treatment readily removes TCC from the liquid waste stream and concentrates the antimicrobial in the solid fraction, which is often processed to produce biosolids intended for land application. Greater than half of the biosolids generated in the US are land-applied, resulting in a systematic release of biosolids-borne TCC into the terrestrial and, potentially, the aquatic environment. Multiple data gaps in the TCC literature (including basic physicochemical properties and biosolids concentrations) prevent an accurate, quantitative risk assessment of biosolids-borne TCC. We utilized the USEPA Office of Prevention, Pesticides, and Toxic Substances (OPPTS) harmonized test guidelines to measure TCC solubility and log K(ow) values as 0.045 mg L(-1) and 3.5, respectively. The measured physicochemical 2 properties differed from computer model predictions. The mean concentration of TCC in 23 biosolids representative of multiple sludge processing methods was 19+/-11 mg kg(-1).