D. van de Meent

Priority assessment of toxic substances in life cycle assessment. Part I: Calculation of toxicity potentials for 181 substances with the nested multi-media fate, exposure and effects model USES-LCA

Toxicity potentials are standard values used in life cycle assessment (LCA) to enable a comparison of toxic impacts between substances. In most cases, toxicity potentials are calculated with multi-media fate models. Until now, unrealistic system settings were used for these calculations. The present paper outlines an improved model to calculate toxicity potentials: the global nested multi-media fate, exposure and effects model USES-LCA. It is based on the Uniform System for the Evaluation of Substances 2.0 (USES 2.0). USES-LCA was used to calculate for 181 substances toxicity potentials for the six impact categories freshwater aquatic ecotoxicity, marine aquatic ecotoxicity, freshwater sediment ecotoxicity, marine sediment ecotoxicity, terrestrial ecotoxicity and human toxicity, after initial emission to the compartments air, freshwater, seawater, industrial soil and agricultural soil, respectively. Differences of several orders of magnitude were found between the new toxicity potentials and those calculated previously.

Heteroaggregation and sedimentation rates for nanomaterials in natural waters

Exposure modeling of engineered nanomaterials requires input parameters such as sedimentation rates and heteroaggregation rates. Here, we estimate these rates using quiescent settling experiments under environmentally relevant conditions. We investigated 4 different nanomaterials (C60, CeO2, SiO2-Ag and PVP-Ag) in 6 different water types ranging from a small stream to seawater. In the presence of natural colloids, sedimentation rates ranged from 0.0001 m d(-1) for SiO2-Ag to 0.14 m d(-1) for C60. The apparent rates of heteroaggregation between nanomaterials and natural colloids were estimated using a novel method that separates heteroaggregation from homoaggregation using a simplified Smoluchowski-based aggregation-settling equation applied to data from unfiltered and filtered waters. The heteroaggregation rates ranged between 0.007 and 0.6 L mg(-1) day(-1), with the highest values observed in seawater. We argue that such system specific parameters are key to the development of dedicated water quality models for ENMs.

Deriving quality criteria for water and sediment from the results of aquatic toxicity tests and product standards: Application of the equilibrium partitioning method

Abstract The present paper summarizes an approach recently proposed in The Netherlands to use the equilibrium partitioning (EP) method to derive a coherent set of quality criteria for aquatic systems. The quality criteria refer to dissolved concentrations, the concentrations in the suspended particles, the total (dissolved + particulate) concentrations and the concentrations in the sediment. The quality criteria have been derived for standard sediment, standard water and standard suspended matter. Emphasis is laid on the relation between effect data and physicochemical data. Two types of effect data have been used, i.e. effects on aquatic toxicity (direct effects) and health related effects (product standards). Both types of data have been translated into the above mentioned criteria by means of EP. For the calculation of criteria in sediment and suspended matter solids-water partition coefficient K sw have been used. Examples have been given for cadmium and hexachlorobenzene. The handled equations have been summarized in diagrams.

A spreadsheet-based box model to predict the fate of xenobiotics in a municipal wastewater treatment plant

Abstract A non-equilibrium steady state box model is reported, that predicts the fate of new chemicals in a conventional sewage treatment plant from a minimal input data set. The model, written in an electronic spreadsheet (Lotus™ 123), requires a minimum input: some basic properties of the chemical, its emission rate and a few parameters to account for the scale and mode of operation of the plant. Compound properties necessary as input are air-water and sludge solids-water partition coefficients. If these distribution coefficients are not available but the compound is hydrophobic, default values are calculated from input such as solubility, vapour pressure and octanol-water partition coefficient. Biodegradability data and the degree of dissociation or protonation are the required input data to account for degradation and speciation changes of the chemical in the water phase. The modelled sewage treatment installation consists of primary sedimentation and the activated sludge technique. The standard output shows the chemicals concentration in effluent and sludge. In addition the output contains the relative amounts degraded and emitted via effluent, sludge and air. The main advantage of this approach is that it provides legislators with a quick insight if a chemical will be an air, water or sludge pollutant when it is discharged into sewage works at a certain rate. Examples are evaluated and results are compared with measured concentrations. Volatilization rates derived from reported field data are in good agreement with predicted emissions to the atmosphere.

Priority assessment of toxic substances in life cycle assessment. Part II: assessing parameter uncertainty and human variability in the calculation of toxicity potentials.

Toxicity potentials are standard values used in life cycle assessment (LCA) to enable a comparison of toxic impacts between substances. This paper presents the results of an uncertainty assessment of toxicity potentials that were calculated with the global nested multi-media fate, exposure and effects model USES-LCA. The variance in toxicity potentials resulting from input parameter uncertainties and human variability was quantified by means of Monte Carlo analysis with Latin Hypercube sampling (LHS). For Atrazine, 2,3,7,8-TCDD and Lead, variation, expressed by the ratio of the 97.5%-ile and the 2.5%-ile, ranges from about 1.5 to 6 orders of magnitude. The major part of this variation originates from a limited set of substance-specific input parameters, i.e. parameters that describe transport mechanisms, substance degradation, indirect exposure routes and no-effect concentrations. Considerable correlations were found between the toxicity potentials of one substance, in particular within one impact category. The uncertainties and correlations reported in the present study may have a significant impact on the outcome of LCA case studies.

New Method for Calculating Comparative Toxicity Potential of Cationic Metals in Freshwater: Application to Copper, Nickel, and Zinc

Current practice in chemical hazard ranking and toxic impact assessments is to estimate fate and toxicity assuming the chemical exists in dissolved and particulate phases and, for metals, that all dissolved species are equally bioavailable. This introduces significant error since metal effects are related to the truly dissolved phase and free metal ion within it, not the total dissolved phase. We introduce a Bioavailability Factor (BF) to the calculation of hazard or Comparative Toxicity Potentials (CTPs) (also known as Characterization Factors; CFs) for use in Life Cycle Impact Assessment (LCIA). The method uses for calculation (1) USEtox for environmental fate, (2) WHAM 6.0 for metal partitioning and speciation in aquatic systems, and (3) Biotic Ligand Model (BLM) for average toxicity. For 12 EU water-types, we calculated medians (range) of CTPs of 1.5 x 10(4) (1.5 x 10(2) to 1.2 x 10(5)), 5.6 x 10(4) (9.4 x 10(3) to 4.1 x 10(5)), and 2.1 x 10(4) (7 x 10(3) to 5.8 x 10(4)) day*m(3)/kg for Cu, Ni, and Zn, respectively, which are up to approximately 1000 times lower than previous values. The greatest contributor to variability in CTPs was the BF, followed by toxicity Effect Factor (EF). The importance of the choice of water-type is shown by changes in the relative ranking of CTPs, which are equally influenced by water chemistry and inherent metal-specific differences.

Guidance for the prognostic risk assessment of nanomaterials in aquatic ecosystems

Our understanding of the environmental fate and effects of engineered nanomaterials (ENMs) is in a state of fast transition. Recent scientific developments open new and powerful perspectives to define a framework for the prognostic risk assessment of ENMs in aquatic ecosystems. This requires abandoning the reductionists approach of mechanistic analysis on particle or cellular scales and calls for engineering solutions that deal with uncertainties by applying assessment factors and probabilistic approaches. An ecological risk assessment (ERA) framework for ENMs is similar to that for other classes of substances, in that it requires clear protection goals based on ecosystem services, evidence-based concepts that link exposure to effects, and a transparent tiered effect assessment. Here, we discuss approaches to assess exposure and effects of ENMs. This includes recent developments in ENP fate modeling that greatly expanded the potential of prognostic exposure assessments. For the effect assessment, we advise a cost-effective screening based on principles of read-across as a conservative first tier. The feasibility of using species sensitivity distributions as a higher tier option is discussed. Controlled model ecosystem field experiments are proposed as a highest experimental tier, and are required for the calibration of the lower tiers. An outlook to unify information from various tiers by experimental work, fate modeling, and effect modeling as cost-effective prognostic tools for the ERA of ENMs is provided.

Estimating overall persistence and long-range transport potential of persistent organic pollutants: a comparison of seven multimedia mass balance models and atmospheric transport models

Two different approaches to modeling the environmental fate of organic chemicals have been developed in recent years. The first approach is applied in multimedia box models, calculating average concentrations in homogeneous boxes which represent the different environmental media, based on intermedia partitioning, transport, and degradation processes. In the second approach, used in atmospheric transport models, the spatially and temporally variable atmospheric dynamics form the basis for calculating the environmental distribution of chemicals, from which also exchange processes to other environmental media are modeled. The main goal of the present study was to investigate if the multimedia mass balance models CliMoChem, SimpleBox, EVn-BETR, G-CIEMS, OECD Tool and the atmospheric transport models MSCE-POP and ADEPT predict the same rankings of the overall persistence (P(ov)) and long-range transport potential (LRTP) of POPs, and to explain differences and similarities between the rankings by the mass distributions and inter-compartment mass flows. The study was performed for a group of 14 reference chemicals. For P(ov), the models yield consistent results, owing to the large influence of phase partitioning parameters and degradation rate constants, which are used similarly by all models. Concerning LRTP, there are larger differences between the models than for P(ov), due to different LRTP calculation methods and spatial model resolutions. Between atmospheric transport models and multimedia fate models, no large differences in mass distributions and inter-compartment flows can be recognized. Deviations in mass flows are mainly caused by the geometrical design of the models.

BasinBox: a generic multimedia fate model for predicting the fate of chemicals in river catchments

Multimedia fate models have proven to be very useful tools in chemical risk assessment and management. This paper presents BasinBox, a newly developed steady-state generic multimedia fate model for evaluating risks of new and existing chemicals in river basins. The model concepts, as well as the intermedia processes quantified in the model, are outlined, and an overview of the required input parameters is given. To test the BasinBox model, calculations were carried out for predicting the fate of chemicals in the river Rhine basin. This was done for a set of 3175 hypothetical chemicals and three emission scenarios to air, river water and cropland soils. For each of these hypothetical chemicals and emission scenarios the concentration ratio between the downstream area and the upstream area was calculated for all compartments. From these calculations it appeared that BasinBox predicts significant concentration differences between upstream and downstream areas of the Rhine river basin for certain types of chemicals and emission scenarios. There is a clear trend of increasing chemical concentrations in downstream direction of the river basin. The calculations show that taking into account spatial variability between upstream, midstream and downstream areas of large river basins can be useful in the predictions of environmental concentrations by multimedia fate models.

Uniform System for the Evaluation of Substances. IV. Distribution and intake.

This is the fourth article in the series on USES, the Uniform System for the Evaluation of Substances. This article describes the modelling approach used to predict concentrations in the environmental media (air, surface water, agricultural soil and groundwater) and the intake media for humans (fish, drinking water, root crops, leaf crops, meat and milk) and for predatory birds and mammals (fish and earthworms). Distribution and intake are estimated on two spatial scales: locally near a point source, and regionally over a larger area. This article focuses on the local distribution and the general intake models. Local distribution is modelled in a hypothetical standard environment, using typical environmental characteristics. Humans and predators are assumed to be exposed to food products from the contaminated system. The choice of models in a system like USES, is limited by the small data sets legally required for risk assessment purposes. Therefore, USES focuses on relatively simple models, and is able to work with the limited input data.