La Direcció General de la Policia 1. Estructura policial

664

A Tiered Approach for Screening Chemicals for Biomagnification Potential in Humans

A. Sangion, University of Insubria / Department of Theoretical and Applied Sciences (DiSTA); J.A. Arnot, ARC Arnot Research & Consulting / Adjunct Professor, Department of Physical & Environmental Science/Department of Pharmacology and Toxicology; P. Gramatica, E. Papa, University of Insubria / Department of Theoretical and Applied Sciences (DiSTA)

Bioaccumulation is a process in which the chemical concentration in an organism exceeds the concentration in the respiratory medium, the diet or both and is an integral aspect of hazard and risk assessment. Strong correlations between partitioning properties such as the octanol-water partition coefficient (Kow) and the octanol-air partition coefficient (Koa) and bioaccumulation metrics in

water-respiring and air-breathing organisms have led to Kow and Koa being the primary screening criteria for bioaccumulation assessment. However, primary biotransformation rate constants (kB) and half-lives (HLB) are also critical determinants of bioaccumulation. Here we present a tiered approach for screening the bioaccumulation potential of organic chemicals in air-breathing organisms. The tiered approach progresses from screening-level conservative assumptions based on Kow and Koa only to more realistic assumptions for, internal distribution, chemical properties and biotransformation (Tiers from 1 to 4 respectively). Biomagnification Factor (BMF) derived from a typical human diet as calculated by the Risk Assessment IDentification And Ranking (RAIDAR) mode is the metric for assessing bioaccumulation potential in air-breathing organisms of approximately 13,000 chemicals including industrial chemicals, pharmaceuticals, personal care products and chemicals used in consumer goods. Tiers that do not consider biotransformation (1, 2 and 3) estimate a high percentage of chemicals with BMF greater than 1 (i.e. about 93%, 95% and 93%). In particular, in Tier 2 and in Tier 3, the introduction of the biotic partition coefficient kStorLipW, kMembLipW and kProtW and about the ionic state at pH 7.4 reduce the BMF estimate for some chemicals, but in general the effects are limited. In Tier 4 the introduction of the HLB has a high impact on the screening results, strongly reducing the BMF estimate to < 1 for most of the compounds (i.e. about 90%). This shows how models based only on partition coefficients are not sufficient to describe and address the bioaccumulation and biomagnification processes, and can lead to overly conservative estimates (“false positives”). Moreover the study highlights the key role of biotransformation in bioaccumulation assessment for air-breathing organisms and highlights the need for reliable data on biotransformation to effectively categorize chemicals for hazard.

665

Critical Evaluation of a Human In Vitro Biotransformation Rate Database: Case Study of Seven Chemicals

K.L. Foster, ARC Arnot Research and Consulting Inc. / Adjunct Professor, Trent University, Applications of Modelling & Quantitative Methods (AMOD); A. Looky, ARC Arnot Research and Consulting Inc.; J.M. Armitage, University of Toronto - Scarborough / Physical and Environmental Sciences; M. Embry, ILSI; J.W. Nichols, U.S. EPA / ORD NHEERL Mid Continent Ecology Division; B. Wetmore, U.S. EPA / National Exposure Research Laboratory; J.A. Arnot, ARC Arnot Research & Consulting / Adjunct Professor, Department of Physical & Environmental Science/Department of Pharmacology and Toxicology

Despite the fundamental value of biotransformation rate information, relatively few measured in vivo data are available for humans compared to the thousands of chemicals requiring evaluation. Reliable models, laboratory measured in vitro biotransformation rate data, and in vitro-in vivo extrapolation (IVIVE) methods can be applied to address in vivo biotransformation rate data gaps and, coupled with data confidence assessment methods, uncertainty and data utility. We have developed a new database of >11,000 human in vitro biotransformation rate estimates (half-lives, clearance rates and rate constants) derived from liver microsomal, S9 homogenate, and hepatocyte-based assays for >8,500 organic chemicals from the literature and publicly available databases (i.e., ChEMBL). The database is comprised primarily of pharmaceuticals and pharmaceutical candidates from various experimental sources. The organic chemicals in the database represent a broad range of physical-chemical properties (Log KOW=-4 to 13, Log KOA=0.01 to 47, Log KAW=-42 to 3) and the in vivo intrinsic clearance values (CLInt,In Vivo mL.h-1_.kg-1_{) span about 8 orders of magnitude. We developed and applied novel} data quality assessment methods based on proposed standardized testing guidance to address variability and uncertainty in the database. The data quality assessment methods included compiling physical-chemical property data (e.g., KOW, pKa, water solubility) for all of the chemicals and applying a mass balance in vitro model. The ensuing data quality scores (e.g., high or low confidence) may help identify datasets that are most appropriate for QSAR development and for other potential applications (e.g., bioaccumulation screening, prioritization). The score results are further examined in a case study of seven chemicals and the utility of high and low confidence biotransformation rate data, its merits and limitations for various use contexts, are discussed and overall key findings of the critical review of existing human in vitro biotransformation rate data are summarized.

666

Sediment-associated cyclic volatile methylsiloxanes: Biotransformation in a

freshwater oligochaete and an estuarine polychaete

H. Selck, Roskilde University / Dept Science and Environment; R. Windfeld, Roskilde University / ENSPAC

Chemical regulatory legislation of organic contaminants is generally based on an assessment of the chemical potential to persist (P) in the environment,

bioaccumulate (B) in biota, and possess potential toxicity. Applying standardized exposure setups (i.e., water-only exposure) as historically has been employed in environmental risk assessment, may underestimate bioaccumulation of hydrophobic organic contaminants (HOCs) in sediment-dwelling organisms because: 1) HOCs often accumulate in sediments to concentrations greatly exceeding the concentration in the overlying water; and 2) a number of papers illustrate that sediment-associated HOCs are available for uptake in benthic organisms. Alternatively, benthic invertebrates may be able to metabolize organic contaminants (i.e., biotransform), thus reducing their body burden. However, available information on the biotransformation capacity of benthic organisms is very limited. We conducted a number of experiments examining uptake and biotransformation of sediment-associated cyclic volatile methylsiloxanes (i.e., D4 and D5) in two deposit-feeding worms, namely, the estuarine polychaete, Capitella

teleta and the freshwater oligochaete, Tubifex tubifex. This presentation will

provide examples of how biotransformation capacity varies among the two benthic deposit feeders, and how biotransformation may reduce body burden and facilitate the removal of sediment-associated siloxanes. Including these factors in a hazard or risk assessment are likely to impact PBT assignment and categorization, and exclusion of benthic organism behaviour may add compound uncertainty to predictions of bioaccumulation and trophic transfer.

667

Toxicokinetics and biotransformation products of diuron and 3,4-DCA in the developing zebrafish embryo (Danio rerio)

E. Jarosz, UFZ Leipzig / Bioanalytical Ecotoxicology; M. Krauss, Helmholtz centre for environmental research - UFZ / Effect-Directed Analysis; S. Aulhorn, Helmholtz Centre for Environmental Research UFZ / Department Bioanalytical Ecotoxicology; E. Küster, Helmholtz Centre for Environmental Research, Dept.Bioanalytical Ecotoxicology / Department Bioanalytical Ecotoxicology; T. Luckenbach, Helmholtz Centre for Environmental Research UFZ / Department Bioanalytical Ecotoxicology

Diuron is a commonly used phenylamide herbicide which acts by interrupting the photosynthetic electron transport chain. Like other phenylamide herbicides diuron is bio-transformed to 3,4-dichloroaniline (3,4-DCA) which occurs in plants, the liver of vertebrates and in soil. Fish embryos do not possess the same metabolic potential as adult fish. It was not determined so far if different embryo stages differ regarding toxicokinetics of diuron and 3,4-DCA and whether toxicities come from parent compounds or metabolites. We addressed the following questions: What are rates of uptake and elimination of diuron and 3,4-DCA in different zebrafish embryo stages? Is diuron biotransformed by the embryo via which metabolic pathway? Does the embryo`s chorion form a barrier for diuron and 3,4-DCA mitigating the compounds` toxicities? Information on these aspects is valuable for the understanding of the toxicity of phenylamide herbicides to fish embryos. For determining tissue concentrations after different times of exposure, freshly fertilized zebrafish eggs were exposed to the EC20(48h) , i.e., for diuron 2,86 mg/L and for 3,4-DCA 1.41 mg/L, pools of 7 embryos were shock-frozen at 13 time points from 1.5 to 120 hours post fertilization (hpf). The test compounds were extracted from the embryo tissue with MeOH/H2O and quantified using liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). Depuration of test chemicals from the embryo tissue was examined in five different developmental stages of embryos that upon exposure to chemicals were transferred to clean medium and then sampled after 0.5, 1.5, 3, 6 and 24 hrs. The tissue concentrations for diuron reached Tmax around 48 hpf, Tmax for 3,4-DCA was between 8 and 24 hpf. Based on the data for internal concentrations upon different exposure times uptake and elimination rate constants (k1, k2) were determined. Both elimination rates and residue of initial concentration after 24 hrs. of depuration differed between embryo stages. The search for possible metabolites showed that 3,4-DCA was transformed into 3,4-dichloroacetanilide in the embryo and two products of N-demethylation of diuron were found. This confirms that both phase I and phase II metabolic enzymes are active from the first hours of embryo development and pinpoints to the biotransformation capability of the zebrafish embryo at this early stage.

668

Application of a generic fish PBTK model for binary mixtures of chemicals

C. Tebby, INERIS / METO; R. Beaudouin, A. Grech, C. Brochot, INERIS / Models for Ecotoxicology and Toxicology METO

The integration of mechanistic approaches in Environmental risk assessment requires the integration of processes to move towards estimating internal dose from exposure or environmental concentrations (external dose) to predict toxicity in each taxa or the whole ecosystem. In this context, the overall objective of this work is to develop models to integrate TK data for environmental risk assessment of single and multiple chemicals. Three steps were defined to fulfil this objective: (i) Data collection of biological, physiological, and toxicological variables to calibrate and develop PBTK models, (ii) Development of PBTK models for environmental risk