Robert W. Gensemer

The biotic ligand model: a historical overview

During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has gained widespread interest amongst the scientific, regulated and regulatory communities because of its potential for use in developing water quality criteria (WQC) and in performing aquatic risk assessments for metals. Specifically, the BLM does this in a way that considers the important influences of site-specific water quality. This journal issue includes papers that describe recent advances with regard to the development of the BLM approach. Here, the current status of the BLM development effort is described in the context of the longer-term history of advances in the understanding of metal interactions in the environment upon which the BLM is based. Early developments in the aquatic chemistry of metals, the physiology of aquatic organisms and aquatic toxicology are reviewed first, and the degree to which each of these disciplines influenced the development of water quality regulations is discussed. The early scientific advances that took place in each of these fields were not well coordinated, making it difficult for regulatory authorities to take full advantage of the potential utility of what had been learned. However, this has now changed, with the BLM serving as a useful interface amongst these scientific disciplines, and within the regulatory arena as well. The more recent events that have led to the present situation are reviewed, and consideration is given to some of the future needs and developments related to the BLM that are envisioned. The research results that are described in the papers found in this journal issue represent a distinct milestone in the ongoing evolution of the BLM approach and, more generally, of approaches to performing ecological assessments for metals in aquatic systems. These papers also establish a benchmark to which future scientific and regulatory developments can be compared. Finally, they demonstrate the importance and usefulness of the concept of bioavailability and of evaluative tools such as the BLM.

Toxicity of ozonated seawater to marine organisms

Ballast water transport of nonindigenous species (NIS) is recognized as a significant contributor to biological invasions and a threat to coastal ecosystems. Recently, the use of ozone as an oxidant to eliminate NIS from ballast while ships are in transit has been considered. We determined the toxicity of ozone in artificial seawater (ASW) for five species of marine organisms in short-term (< or = 5 h) batch exposures. Larval topsmelt (Atherinops affinis) and juvenile sheepshead minnows (Cyprinodon variegatus) were the most sensitive to oxidant exposure, and the mysid shrimp (Americamysis bahia) was the most sensitive invertebrate. Conversely, benthic amphipods (Leptocheirus plumulosus and Rhepoxinius abronius) were the least sensitive of all species tested. Mortality from ozone exposure occurred quickly, with median lethal times ranging from 1 to 3 h for the most sensitive species, although additional mortality was observed 1 to 2 d following ozone exposure. Because ozone does not persist in seawater, toxicity likely resulted from bromide ion oxidation to bromine species (HOBr and OBr-), which persist as residual toxicants after at least 2 d of storage. Total residual oxidant (TRO; as Br2) formation resulting from ozone treatment was measured in ASW and four site-specific natural seawaters. The rate of TRO formation correlated with salinity, but dissolved organic carbon and total dissolved nitrogen did not affect TRO concentrations. Acute toxicity tests with each water over 48 h using mysid shrimp, topsmelt, and sheepshead minnows yielded results similar to those of batch exposure. Addition of sodium thiosulfate (Na2S2O3) to ozonated waters resulted in TRO elimination and survival of all organisms. Our results provide necessary information for the optimization of an efficacious ozone ballast water treatment system.

Evaluating the role of ion composition on the toxicity of copper to Ceriodaphnia dubia in very hard waters.

The mitigating effect of increasing hardness on metal toxicity is reflected in water quality criteria in the United States over the range of 25-400 mgl(-1) (as CaCO(3)). However, waters in the arid west of the US frequently exceed 400 mgl(-1) hardness, and the applicability of hardness-toxicity relationships in these waters is unknown. Acute toxicity tests with Ceriodaphnia dubia were conducted at hardness levels ranging from approximately 300 to 1,200 mgl(-1) using reconstituted waters that mimic two natural waters with elevated hardness: (1) alkaline desert southwest streams (Las Vegas Wash, NV), and (2) low alkalinity waters from a CaSO(4)-treated mining effluent in Colorado. The moderately-alkaline EPA synthetic hard water was also included for comparison. Copper toxicity did not consistently vary as a function of hardness, but likely as a function of other water quality characteristics (e.g., alkalinity or other correlated factors). The hardness equations used in regulatory criteria, therefore, may not provide an accurate level of protection against copper toxicity in all types of very hard waters. However, the mechanistic Biotic ligand model generally predicted copper toxicity within +/-2X of observed EC(50) values, and thus may be more useful than hardness for modifying water quality criteria.

Shipboard trials of an ozone-based ballast water treatment system

Legislation introduced by the United Nations International Maritime Organization (IMO) has focused primarily on standards defining successful treatments designed to remove invasive species entrained in ballast water. An earlier shipboard study found that ozone introduced into salt water ballast resulted in the formation of bromine compounds, measured as total residual oxidants (TRO) that were toxic to both bacteria and plankton. However, the diffuser system employed to deliver ozone to the ballast water tanks resulted in patchiness in TRO distribution and toxicity to entrained organisms. In this follow-up study, the shipboard diffuser system was replaced by a single Venturi-type injection system designed to deliver a more homogeneous biocide distribution. Within-tank variability in TRO levels and associated toxicity to zooplankton, phytoplankton and marine bacteria was measured via a matrix of tubes deployed to sample different locations in treated and untreated (control) tanks. Three trials were conducted aboard the oil tanker S/T Prince William Sound in the Strait of Juan de Fuca off Port Angeles, Washington State, USA, between June and December 2007. Mortalities of plankton and bacteria and oxidant concentrations were recorded for treated and untreated ballast water up to 3days following treatment, and residual toxicity beyond this period was measured by bioassay of standard test organisms. Results indicated uniform compliance with current IMO standards, but only partial compliance with other existing and pending ballast water legislation.

COMPARATIVE EFFECTS OF pH AND ALUMINUM ON SILICA‐LIMITED GROWTH AND NUTRIENT UPTAKE IN ASTERIONELLA RALFSII VAR. AMERICANA (BACILLARIOPHYCEAE)1

The acidophilic diatom Asterionella ralfsii cf. var. americana Körn. was grown in continuous culture to examine the influences of both pH and Al on Si‐limited growth and uptake kinetics. In contrast to nutrient‐replete cultures of A. ralfsii, lowering pH from approximately 6 to 5 reduced algal cell density, chlorophyll a concentration, and intensity of in vivo fluorescence (IVF) at steady state. The lower pH treatments were also characterized by lower Si cell quotas and higher residual dissolved Si concentrations in chemostats with similar nutrient supply rates. Physiological responses to Al stress differed from those to pH reduction when cultures were Si‐limited. Nominal Al additions of 20 μmol·L−1 reduced chlorophyll a concentration and IVF values at higher pH, but all other biomass and chemical parameters remained constant at steady state. The combined efects of Al and reduced pH were more severe than either stress alone, inducing culture washout at pH 4.8. Short‐term Si uptake experiments performed at pH 6 showed that Al influenced Michaelis‐Menten parameter estimates. Half‐saturation (Ks and maximum uptake rate (Vm) constants increased approximately 8‐ and 2‐fold in the presence of Al, respectively, but this difference was only significant for Vm. Similar to previously observed effects of Al on cell morphology in A. ralfsii, Si uptake kinetics were more sensitive to Al additions than to Silimited growth per se.

Evaluating the effects of pH, hardness, and dissolved organic carbon on the toxicity of aluminum to freshwater aquatic organisms under circumneutral conditions

Although it is well known that increasing water hardness and dissolved organic carbon (DOC) concentrations mitigate the toxicity of aluminum (Al) to freshwater organisms in acidic water (i.e., pH < 6), these effects are less well characterized in natural waters at circumneutral pHs for which most aquatic life regulatory protection criteria apply (i.e., pH 6-8). The evaluation of Al toxicity under varying pH conditions may also be confounded by the presence of Al hydroxides and freshly precipitated Al in newly prepared test solutions. Aging and filtration of test solutions were found to greatly reduce toxicity, suggesting that toxicity from transient forms of Al could be minimized and that precipitated Al hydroxides contribute significantly to Al toxicity under circumneutral conditions, rather than dissolved or monomeric forms. Increasing pH, hardness, and DOC were found to have a protective effect against Al toxicity for fish (Pimephales promelas) and invertebrates (Ceriodaphnia dubia, Daphnia magna). For algae (Pseudokirchneriella subcapitata), the protective effects of increased hardness were only apparent at pH 6, less so at pH 7, and at pH 8, increased hardness appeared to increase the sensitivity of algae to Al. The results support the need for water quality-based aquatic life protection criteria for Al, rather than fixed value criteria, as being a more accurate predictor of Al toxicity in natural waters. Environ Toxicol Chem 2018;37:49-60.

Chronic toxicity of aluminum, at a pH of 6, to freshwater organisms: Empirical data for the development of international regulatory standards/criteria

The chemistry, bioavailability, and toxicity of aluminum (Al) in the aquatic environment are complex and affected by a wide range of water quality characteristics (including pH, hardness, and dissolved organic carbon). Data gaps in Al ecotoxicology exist for pH ranges representative of natural surface waters (pH 6-8). To address these gaps, a series of chronic toxicity tests were performed at pH 6 with 8 freshwater species, including 2 fish (Pimephales promelas and Danio rerio), an oligochaete (Aeolosoma sp.), a rotifer (Brachionus calyciflorus), a snail (Lymnaea stagnalis), an amphipod (Hyalella azteca), a midge (Chironomus riparius), and an aquatic plant (Lemna minor). The 10% effect concentrations (EC10s) ranged from 98 μg total Al/L for D. rerio to 2175 μg total Al/L for L. minor. From these data and additional published data, species-sensitivity distributions (SSDs) were developed to derive concentrations protective of 95% of tested species (i.e., 50% lower confidence limit of a 5th percentile hazard concentration [HC5-50]). A generic HC5-50 (not adjusted for bioavailability) of 74.4 μg total Al/L was estimated using the SSD. An Al-specific biotic ligand model (BLM) was used to develop SSDs normalized for bioavailability based on site-specific water quality characteristics. Normalized HC5-50s ranged from 93.7 to 534 μg total Al/L for waters representing a range of European ecoregions, whereas a chronic HC5 calculated using US Environmental Protection Agency aquatic life criteria methods (i.e., a continuous criterion concentration [CCC]) was 125 μg total Al/L when normalized to Lake Superior water in the United States. The HC5-50 and CCC values for site-specific waters other than those in the present study can be obtained using the Al BLM. Environ Toxicol Chem 2018;37:36-48.

Protectiveness of water quality criteria for copper in western United States waters relative to predicted olfactory responses in juvenile Pacific salmon

Copper (Cu) can impair olfaction in juvenile Pacific salmon (as well as other fishes), thus potentially inhibiting the ability of juveniles to avoid predators or to find food. Because Cu is commonly elevated in stormwater runoff in urban environments, storm events may result in elevated Cu concentrations in salmon-bearing streams. Accordingly, there is concern that existing Cu criteria, which were not derived using data for olfactory-related endpoints, may not be adequately protective of juvenile salmon. However, a modification of the US Environmental Protection Agency (USEPA) biotic ligand model (BLM) for deriving site-specific Cu criteria was recently proposed, which accounted for the sensitivity of olfactory endpoints. The modification was based on olfactory inhibition in juvenile coho salmon (Oncorhynchus kisutch) exposed to Cu in various combinations of pH, hardness, alkalinity, and dissolved organic carbon (DOC) concentrations. We used that olfactory-based BLM to derive 20% inhibition concentrations (IC20) values for Cu for 133 stream locations in the western United States. The olfactory BLM-based IC20 values were compared to the existing hardness-based Cu criteria and the USEPAs BLM-based Cu criteria for these representative natural waters of the western United States. Of the 133 sampling locations, mean hardness-dependent acute and chronic Cu criteria were below the mean olfactory-based BLM IC20 value in 122 (92%) and 129 (97%) of the waters, respectively (i.e., <20% olfactory impairment would have been predicted at the mean hardness-based Cu criteria concentrations). Waters characterized by a combination of high hardness and very low DOC were most likely to have hardness-based Cu criteria that were higher than the olfactory-based BLM IC20 values, because DOC strongly influences Cu bioavailability in the BLM. In all waters, the USEPAs current BLM-based criteria were below the mean olfactory-based BLM IC20 values, indicating that the USEPAs BLM-based criteria are protective of olfactory impairment in juvenile salmon.

Aluminum bioavailability and toxicity to aquatic organisms: Introduction to the special section

The ability to accurately predict the aquatic toxicity of aluminum (Al) in natural surface waters has eluded scientists for the past several decades. In the 1980s, the acid rain program, supported by theUSEnvironmental ProtectionAgency (USEPA), identifiedAl in low-pH natural waters as a potential concern because of the presence of Al3þ. Most of the studies conducted at that timewere performed at a pH of 6 or lower and in waters with low dissolved organic carbon (DOC) and hardness concentrations; there was little direct consideration of variables affecting Al bioavailability. However, chemical species of Al differ substantially across the pH rangeof6 to8 found inmostnatural surfacewaters.Aluminumcan bepresent as inorganic hydroxy species (Al3þ, AlOH2þ, Al[OH]2 þ, Al[OH]3 , and Al[OH]4 ), as inorganic complexes with fluoride (F) and sulfate (SO4 ), and as weak and strong complexes with organic material [1]. In 1988, the USEPA released nationally recommended ambient water quality criteria for Al of 750 and 87mg/L as acute and chronic criteria, respectively [2]. However, these were derived to apply only to waters with pH between 6.5 and 9, and so they were based on a relatively small toxicity database. In 2009, therefore, we assembled a team of biologists, ecotoxicologists, biochemists, chemical engineers, and chemists to help expand this database and identify a means for measuring and predicting the toxicity of Al to aquatic organisms as a function of water chemistry. To address data gaps for pH ranges more representative of typical natural waters (pH 6–8), a series of chronic toxicity tests was performed, initially at pH 6.0 to 6.3 and with some studies at higher pH values, with 9 freshwater species: 2 fish species (the fathead minnow, Pimephales promelas, and zebrafish, Danio rerio), an aquatic oligochaete (Aeolosoma sp.), a rotifer (Brachionus calyciflorus), the great pond snail (Lymnaea stagnalis), an amphipod (Hyalella azteca), a midge (Chironomus riparius), a unionid mussel (Lampsilis siliquoidea), and a plant (duckweed, Lemna minor) [3–5]. The species were selected to meet the USEPA requirements for developing ambient water quality criteria or the European guidelines for developing predicted-no-effect concentrations under the Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) regulation [6]. For the purpose of developing toxicity bioavailability models, multiple tests with a green alga (Pseudokirchneriella subcapitata), a cladoceran (Ceriodaphnia dubia), and a fish (fathead minnow) were performed across a range of DOC, hardness, and pH conditions.

Scientific Review of Cyanide Ecotoxicology and Evaluation of Ambient Water Quality Criteria

The USEPAs ambient water quality criteria (AWQC) for cyanide were developed in 1984. Recently, however, concerns have arisen that the AWQC for cyanide have been problematic to implement and may not accurately reflect either the toxic forms or bioavailable concentrations of cyanide in water, sediments, and tissues of aquatic organisms. Also, the cyanide criteria typically have been implemented based on total cyanide concentrations rather than the free cyanide concentrations that formed the basis of the criteria calculations. New knowledge on cyanide toxicity, cyanide speciation and its measurement, and the relative toxicity of bioavailable cyanide species suggested that a re-evaluation of the aquatic toxicity data and chemistry that serve as the basis of the current national criteria is warranted. In response to these concerns, studies sponsored by the Water Environment Research Foundation (WERF) evaluated the formation and fate of cyanide in municipal wastewater effluents. Kavanaugh et al. (2003) evaluated the reliability of several analytical methods for measurement of cyanide species at low (ppb) concentrations, along with studies to evaluate the sources, transport, and fate of cyanide species in wastewater treatment plants (WWTPs) and receiving waters. Results indicated that potentially toxic forms of cyanide can be generated in WWTPs from several chemical processes, including dissociation of thiocyanate by chlorination or UV disinfection, chlorination in the presence of residual ammonia, nitrosation, and photolysis of ferrocyanate. Models were developed for predicting the fate of these compounds in surface waters downstream of WWTP effluents to establish where organisms might be most at risk from cyanide exposure. While implementation of these results could assist in the development of site-specific water quality standards for cyanide, a more thorough update to the National AWQC was warranted to apply our more current scientific understanding of cyanide toxicology to the derivation of aquatic life criteria. The present study was therefore undertaken to review and update knowledge of the aquatic toxicity of cyanide, and to develop recommended updates to the existing national AWQC to enhance the scientific basis of the concentrations and chemical forms of cyanide specified for protection of aquatic organisms. This update was conducted according to USEPA guidance for derivation of AWQC for protection of aquatic life, and is based both on an extensive literature review and on new toxicity studies that fill key data gaps. This re-evaluation of cyanide criteria also includes consideration of impacts on benthic (sediment) organisms, wildlife that consume aquatic biota, and possible effects to threatened and endangered species to ensure that revised criteria are adequately protective of the entire aquatic ecosystem. This title belongs to WERF Research Report Series ISBN: 9781843397533 (Print) ISBN: 9781780403755 (eBook)