TKPlate 1.0: An Open-access platform for toxicokinetic and toxicodynamic modelling of chemicals to implement new approach methodologies in chemical risk assessment.

This publication is linked to the following EFSA Supporting Publications articles: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2023.EN-8441/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2023.EN-8440/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2023.EN-8437/full.

In Silico Methods for Environmental Risk Assessment: Principles, Tiered Approaches, Applications, and Future Perspectives.

This chapter aims to introduce the reader to the basic principles of environmental risk assessment of chemicals and highlights the usefulness of tiered approaches within weight of evidence approaches in relation to problem formulation i.e., data availability, time and resource availability. In silico models are then introduced and include quantitative structure-activity relationship (QSAR) models, which support filling data gaps when no chemical property or ecotoxicological data are available. In addition, biologically-based models can be applied in more data rich situations and these include generic or species-specific models such as toxicokinetic-toxicodynamic models, dynamic energy budget models, physiologically based models, and models for ecosystem hazard assessment i.e. species sensitivity distributions and ultimately for landscape assessment i.e. landscape-based modeling approaches. Throughout this chapter, particular attention is given to provide practical examples supporting the application of such in silico models in real-world settings. Future perspectives are discussed to address environmental risk assessment in a more holistic manner particularly for relevant complex questions, such as the risk assessment of multiple stressors and the development of harmonized approaches to ultimately quantify the relative contribution and impact of single chemicals, multiple chemicals and multiple stressors on living organisms.

EFSA's OpenFoodTox: An open source toxicological database on chemicals in food and feed and its future developments.

Since its creation in 2002, the European Food Safety Authority (EFSA) has produced risk assessments for over 5000 substances in >2000 Scientific Opinions, Statements and Conclusions through the work of its Scientific Panels, Units and Scientific Committee. OpenFoodTox is an open source toxicological database, available both for download and data visualisation which provides data for all substances evaluated by EFSA including substance characterisation, links to EFSA's outputs, applicable legislations regulations, and a summary of hazard identification and hazard characterisation data for human health, animal health and ecological assessments. The database has been structured using OECD harmonised templates for reporting chemical test summaries (OHTs) to facilitate data sharing with stakeholders with an interest in chemical risk assessment, such as sister agencies, international scientific advisory bodies, and others. This manuscript provides a description of OpenFoodTox including data model, content and tools to download and search the database. Examples of applications of OpenFoodTox in chemical risk assessment are discussed including new quantitative structure-activity relationship (QSAR) models, integration into tools (OECD QSAR Toolbox and AMBIT-2.0), assessment of environmental footprints and testing of threshold of toxicological concern (TTC) values for food related compounds. Finally, future developments for OpenFoodTox 2.0 include the integration of new properties, such as physico-chemical properties, exposure data, toxicokinetic information; and the future integration within in silico modelling platforms such as QSAR models and physiologically-based kinetic models. Such structured in vivo, in vitro and in silico hazard data provide different lines of evidence which can be assembled, weighed and integrated using harmonised Weight of Evidence approaches to support the use of New Approach Methodologies (NAMs) in chemical risk assessment and the reduction of animal testing.

Toxic equivalency factors (TEFs) for PCBs, PCDDs, PCDFs for humans and wildlife.

An expert meeting was organized by the World Health Organization (WHO) and held in Stockholm on 15-18 June 1997. The objective of this meeting was to derive consensus toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and dioxinlike polychlorinated biphenyls (PCBs) for both human, fish, and wildlife risk assessment. Based on existing literature data, TEFs were (re)evaluated and either revised (mammals) or established (fish and birds). A few mammalian WHO-TEFs were revised, including 1,2,3,7,8-pentachlorinated DD, octachlorinated DD, octachlorinated DF, and PCB 77. These mammalian TEFs are also considered applicable for humans and wild mammalian species. Furthermore, it was concluded that there was insufficient in vivo evidence to continue the use of TEFs for some di-ortho PCBs, as suggested earlier by Ahlborg et al. [Chemosphere 28:1049-1067 (1994)]. In addition, TEFs for fish and birds were determined. The WHO working group attempted to harmonize TEFs across different taxa to the extent possible. However, total synchronization of TEFs was not feasible, as there were orders of a magnitude difference in TEFs between taxa for some compounds. In this respect, the absent or very low response of fish to mono-ortho PCBs is most noticeable compared to mammals and birds. Uncertainties that could compromise the TEF concept were also reviewed, including nonadditive interactions, differences in shape of the dose-response curve, and species responsiveness. In spite of these uncertainties, it was concluded that the TEF concept is still the most plausible and feasible approach for risk assessment of halogenated aromatic hydrocarbons with dioxinlike properties.

Selected polyhalogenated hydrocarbons in breast milk.

Breast milk samples were collected and analysed within a comprehensive programme co-ordinated by WHO EURO to evaluate the possible health risk for breast-fed infants in chosen localities of European countries ('exposed' and 'control' ones). The samples of breast milk were collected, stored transported and analysed by a standardised study protocol to assure the comparability of the results from different areas (of 19 European countries). The study included three categories of chemicals: polychlorinated dibenzo-p-dioxins (PCDDs)/polychlorinated dibenzofurans (PCDFs), dioxine like polychlorinated biphenyls (PCBs) and other PCBs. The results obtained confirmed the correct choice of 'exposed' and 'control' regions in the Czech Republic as a suitable tool used to identify certain geographical areas with relatively high exposure levels for further risk management actions and possible follow-up epidemiological studies. The results obtained have shown high levels of PCBs in exposed region but not in the dioxine-like fraction, that ranged within a lower rank of a relevant European data. PCDs/PCDFs levels ranged in the same lower rank of values in comparison with e.g. Benelux countries. The data of this study does not confirm ideas about wide spread excessive exposure of central European population to polyhalogenated hydrocarbons via excessive contamination of a local food basket.

Dioxins, dioxin-like PCBs and non-dioxin-like PCBs in foodstuffs: occurrence and dietary intake in The Netherlands.

Data on occurrence of dioxins (polychlorinated dibenzo-p-dioxins [PCDDs] and dibenzofurans [PCDFs]), dioxin-like PCBs (polychlorinated non-ortho and mono-ortho biphenyls) and non-dioxin-like PCBs (as represented by the so-called indicator-PCBs: congeners 28, 52, 101, 118, 138, 153 and 180) in food products consumed in The Netherlands that were collected in measurement programs carried out during 1998 and 1999, and combined with food consumption data to assess the dietary intake of these persistent food contaminants. The estimated median life-long-averaged intake of the sum of dioxins and dioxin-like PCBs in the population is 1.2 pg WHO-TEQ (toxic equivalents) per kg body weight (bw) per day, while the estimated median life-long-averaged intake of indicator-PCBs is 5.6 ng per kg bw per day. The contribution of different food groups to the total intake of both dioxins + dioxin-like PCBs and non-dioxin-like PCBs is fairly uniformly distributed over the foods consumed: meat products (23% and 27%, respectively), dairy products (27% and 17%, respectively), fish (16% and 26%, respectively), eggs (4% and 5%, respectively), vegetable products (13% and 7%, respectively), and industrial oils and fats (17% and 18%, respectively). Compared with earlier intake estimations the present estimation shows a continued reduction in the intake of dioxins as well as PCBs. This reduction is related to the decrease in the concentration of these substances in the majority of foodstuffs. Nevertheless, a small part of the population still has a rather high life-long averaged intake: 8% of the population is exposed to intake levels above the tolerable weekly intake for dioxins and dioxin-like PCBs of 14 pg WHO-TEQ per kg bw per week, as recently derived by the Scientific Committee on Food of the European Commission. For the non-dioxin-like PCBs an internationally accepted maximum intake level is still lacking. However, to provide risk managers with a health-based guideline to prevent health effects of exposure to non-dioxin-like PCBs, the (international) derivation of a tolerable daily intake is recommended. Monitoring the dietary intake of PCBs is just as important as monitoring the intake of dioxins and dioxin-like PCBs, and attempts to decrease the exposure to both compound classes need continuous attention.

Short term fasting does not aggravate immunosuppression in harbour seals (Phoca vitulina) with high body burdens of organochlorines.

Two groups of 11 harbour seals (Phoca vitulina) with different body burdens of organochlorines were subjected to an experimental 15-day fasting period, during which they lost an average 16.5% of their body weights. Blood levels of the most persistent organochlorines showed an approximate twofold increase, while levels of aryl hydrocarbon receptor-binding organochlorines remained largely unaffected. Few differences in immunological parameters were observed between the two dietary groups. Numbers of circulating lymphocytes dropped to about 65% of the initial values and NK cell activity showed a slight increase in both groups. Mitogen- and antigen-induced lymphoproliferative responses of the Baltic group of seals remained within normal ranges. These results suggest that relatively short-term fasting periods do not present an additional immunotoxicological risk to seals with high body burdens of organochlorines.

The Monostrut prosthetic valve. Predictors for valve-related events during an eight years' experience.

All postoperative complications, including transient ischaemic attacks (TIA) and cerebrovascular accidents (CVA) of 259 patients, in whom a total of 301 Monostrut tilting-disc valves were implanted between January 1985 and December 1991 were evaluated retrospectively. The follow-up was maximally 8 years, with a mean of 3.5 years, and totaled 914 patient-years. In this study we found no mechanical deterioration of the Monostrut valve and demonstrated the elimination of valve thrombosis in patients receiving adequate anticoagulation. The actuarial probability of being free of thrombo-embolism was 94.7% +/- 1.7% and free of anticoagulant related hemorrhage 95.4% +/- 1.5% at 8-years. In comparison with earlier reports by others, our findings show a lower ratio of thromboembolic and hemorrhagic events. We demonstrated a correlation (p < 0.05) between thrombo-embolic and hemorrhagic complications. In addition, a lower incidence of CVA's (0.22 per 100 patient-years), but a higher incidence of TIA's (0.66 per 100 patient-years) in comparison with the general Dutch population was found. At eight years follow-up, all patients were in Class I or II of the New York Heart Association Classification. Although the overall valve related event-free survival at eight years was only 47.9%, 93.5% of the patient were satisfied with their operative result. Predictive factors for late mortality were the occurrence of paravalvular leakage (p < 0.01), the age of the patient at the time of operation (p < 0.01) and the number of diseases coronary arteries (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Dioxins and related compounds: Status and regulatory aspects.

Several countries have put much effort in dioxin research programmes with the aim to assess the risks of dioxin exposure, to identify dioxin sources and to quantify their contribution to environmental emissions and human exposure. In this review, the accent has been put on: sources of dioxins and their contribution to the total dioxin emissions, sources of human exposure and their contribution to exposure and measures to reduce emission and exposure. The information from countries with existing dioxin regulations is reviewed and compared. Uncertainties which hamper comparability of data are indicated. Results of measures and expectations for the near future are presented.

Study of polychlorinated dibenzodioxins and furans from municipal waste incinerator emissions in The Netherlands: analytical methods and levels in the environment and human food chain.

An overview is given of the methods that have been used in the study of polychlorodibenzo-p-dioxins and polychlorodibenzofurans in agriculture and the human food chain in a national survey and monitoring programme, including sampling strategies, sampling in the field and clean-up and analysis in various biological and environmental samples by high-resolution gas chromatography-high resolution mass spectrometry. The quality of data was evaluated as a result of internal quality control protocols and participation in interlaboratory comparison studies. Statistical analysis techniques and modelling were applied in order to compare and relate congener profiles in various matrices and to evaluate levels found in field studies for their use for regulatory purposes.

Exposure of populations to dioxins and related compounds.

The present situation with respect to the exposure of the general human population to PCDDs, PCDFs and (dioxin-like) PCBs and specific issues that should be taken into consideration for a risk assessment of these exposures have been summarized. The information is based on studies performed in The Netherlands and Germany in the last 10 years. Additional data have been collected through a literature search and through many contacts with researchers and national authorities. The most important route for human exposure to PCDDs, PCDFs and (dioxin-like) PCBs is food consumption contributing over 90% of total exposure, with products of animal origin and fish making the greatest contribution to this exposure. The dietary intake of PCDDs and PCDFs by the general population of industrialized countries is on average 1-3 picograms of (i)-TEQ per kilogram body weight per day. If the contribution of dioxin-like PCBs are also considered, the daily TEQ intake can be a factor of two to three higher. Special consumption habits and consumption of highly contaminated foodstuffs may lead to lower and higher TEQ intakes. In general, TEQ intake increases during childhood and stabilizes in adults of about 20 years of age. However, when normalized by body weight exposure is found to decrease with childhood age due to increasing body weight. Exposure has been shown to have fallen over time in all countries where data are available. Countries that started to implement measures to reduce dioxin emissions in the late 1980s, such as The Netherlands, United Kingdom and Germany, clearly show decreasing PCDD/PCDF and PCB levels in food and consequently a significantly lower dietary intake of these compounds by almost a factor of 2 within the past 7 years.

Supercritical fluid extraction of polychlorinated biphenyls and pesticides from soil. Comparison with other extraction methods.

A comparison is made of supercritical fluid extraction (SFE) with two other techniques widely used for the extraction of polychlorinated biphenyls (PCBs) and organochlorine pesticides in soil. Extraction conditions for the SFE of PCBs and pesticides were first determined. An experimental approach was set up to determine the influence of different extraction parameters such as pressure, extraction time, static and dynamic extraction, restrictor type and collection solvent for off-line SFE. The use of carbon dioxide at 50 degrees C and 20 MPa, 10 min static followed by 20 min dynamic extraction with collection in iso-octane were been found to be the optimum conditions. Two types of soil, with a low and high content of organic carbon, respectively, spiked with 16 PCBs and organochlorine pesticides with a wide range of volatility and polarity at a level of 5 ng/g dry matter, were used as test materials. Conventional solvent extraction gives a good extraction yield for soil with a low content of organic carbon, but for peat soil the recoveries decrease dramatically to 30% for DDE, DDT and PCB 138 and 153. The recoveries with Soxhlet extraction are good, but an extra clean-up step before analysis is necessary. SFE gives good extraction yields for PCBs and organochlorine pesticides, varying between 85 and 105% with a reproducibility of 5% for each component for both types of soil. SFE is a fast, clean and reproducible method for the extraction of PCBs and organochlorine pesticides from these two soil matrices.

Factors that influence the level of contamination of human milk with poly-chlorinated organic compounds.

Polychlorinated organic compounds (POCs) accumulate in tissues with a high fat content. Nursed babies are exposed to POCs through the fat in human milk. Exposure levels are estimated to exceed those considered acceptable as a lifelong daily dose. Nevertheless, mothers are still positively advised as to breast-feeding. In 1988, a survey on contamination of human milk with POCs was carried out in The Netherlands. Levels of ten different organochlorine pesticides (OCPs), eight polychlorinated biphenyl (PCB) congeners, and seventeen polychlorinated dibenzodioxin (PCDD) and -dibenzofuran (PCDF) congeners were determined by use of gaschromatographic techniques with either electron-capture or mass-spectrometric detection. Information on some factors potentially influencing the level of contamination of human milk was obtained by questionnaires. The estimated response amounted to 71 percent. Regression analysis was used to investigate associations between determining factors and specific contaminants. It appeared that maternal age was positively associated with POC concentrations. Traditional omnivorous diet was associated with lower concentrations of POCs when compared to all other types of diet. The post-pregnancy Quetelet Index [by definition calculated as weight/(length)2] and the cumulated period of previous breast-feeding were negatively associated with POC concentrations. In conclusion, chemical behavior and environmental distribution patterns of the POCs measured in this study, if translated to factors of human exposure, are in accordance with the study results. Exposure levels will decrease if emissions can be further reduced. Still, in the near future, maternal age will probably rise (Vermunt 1992; Netherlands Central Bureau of Statistics 1992), whereas the duration of lactation in expected to decline. Consequently, there might be an increase in average POC-concentrations in human milk in the forthcoming years.

Analysis of organic micropollutants in the lipid fraction of foodstuffs.

An overview is given of current techniques for the analysis of organic micropollutants that accumulate in the fatty fraction of foodstuffs, such as pesticides, polychlorinated biphenyls, polycyclic aromatic hydrocarbons, polychlorinated dibenzodioxins and polychlorinated dibenzofurans. Isolation and clean-up are considered to be of great importance in the field of residue analysis. In general, problems are related to the low levels of the individual compounds at which they usually occur and the complexity of extraction and clean-up procedures for isolating and separating analytes from matrix components and other contaminants. Therefore, special attention is focused on sample pretreatment and on coupled chromatographic techniques, showing developments towards multi-residue methods, miniaturization and automation of analytical procedures. Coupling of chromatographic techniques with spectroscopic techniques is also considered as an important tool for identification and confirmation purposes.

Toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) to the human thymus after implantation in SCID mice.

There are conflicting data with regard to the sensitivity of the human immune system to the toxic action of the highly toxic environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). SCID mice engrafted with human fetal thymus and liver tissue fragments (SCID-hu mice), which sustain normal human T cell differentiation in the thymus graft, were used to directly assess the sensitivity of the human thymus for TCDD. Wistar rats and SCID-hu mice were exposed to 1, 5 or 25 micrograms TCDD/kg body weight. Histopathologic effects were evaluated for rat thymus and transplanted human thymus on Day 4 after exposure. The relative size of the cortex showed a dose-dependent decrease in both the normal rat thymus and grafted human thymus (significant at 25 micrograms/kg). SCID-ra mice (SCID mice with a fetal rat thymus and liver graft) were used as an intermediate model between the normal rat and SCID-hu mice, and were exposed to the same dose levels of TCDD. However, 90% of the SCID-ra mice developed a cutaneous graft-versus-host reaction, associated with lymphodepletion of the rat thymus grafts, and hence a limited number of SCID-ra mice were available for evaluation of TCDD effects. The data obtained in SCID-ra mice were in line with those in normal rat and grafted human thymus. In gas chromatography/mass spectrometry analysis, TCDD tissue concentrations in the normal rat thymus and grafted human thymus were similar. We conclude that the human thymus serves as a target for TCDD, and that the human thymus and the Wistar rat thymus display a comparable sensitivity to the toxic action of TCDD.

Levels of certain metals, organochlorine pesticides and dioxins in cord blood, maternal blood, human milk and some commonly used nutrients in the surroundings of the Aral Sea (Karakalpakstan, Republic of Uzbekistan).

UNLABELLED: Since the 1960s a massive decline in the volume of the Aral Sea has occurred as a result of the diversion of the supplying rivers to cotton irrigation schemes. The contaminated sediment of the former seabed has been disseminated over the surrounding area by strong winds. This deterioration of the ecosystem has created a hazardous situation for the health of approximately 3.5 million people. This pilot study was undertaken to assist Karakalpak health workers in investigating the degree of exposure to metals, persistent organochlorine pesticides (OCPs) and dioxins during the most vulnerable prenatal and postnatal period and to provide guidelines for future research. All subjects came from areas located within 200 km of the southern border of the Aral Sea. Blood was obtained from 18 pregnant women and 28 newborns (cord blood) to determine the levels of metals, lead, cadmium, zinc and selenium and the OCPs alpha-, beta- and gamma-hexachlorocyclohexane (HCH; lindane is the product name of gamma-hexachlorocyclohexane), hexachlorobenzene (HCB), and isomers and metabolites of dichlorodiphenyltrichloroethane (DDT), i.e. op-DDT, pp-DDT, pp-DDE and pp-TDE. Levels of metals were also determined in blood from 28 non-pregnant women. In addition, levels of 17 dioxins were determined in 41 human milk samples and 1batch of formula. Information about possible dietary sources of the fat-soluble OCPs and dioxins was obtained from a pooled sample of butter and from seven cottonseed oil samples. A mass-selective detector coupled to a gas chromatograph equipped with a large volume injector was used to analyse the selected OCPs, whereas the dioxins were determined by gas chromatography with high-resolution mass spectrometry. The levels of metals in cord and maternal blood were consistent with concentrations observed in European countries. Only three women (7%) had lead levels greater than 100 ppb. The most notable pollutants in maternal and cord blood were the OCPs, notably HCB, beta-HCH, pp-DDE and the most toxic dioxin, 2,3,7,8-TCDD, when calculated as TEQs. A similar pattern was observed in human milk: beta-HCH and pp-DDE levels of more than 1,000 ng g(-1) fat were found in 68 and 43% of the subjects, respectively. Levels of 2,3,7,8-TCDD were six times higher than those observed in Western Europe. Traces of pp-DDE were detected in the batch of formula milk. Contaminated animal fat, but not cottonseed oil, is the most likely dietary source of OCPs and dioxins. CONCLUSION: Further epidemiological research is needed to elucidate the health implications of these pollutants on perinatal and maternal health, including lactation. More importantly, an investigation should be initiated to identify the emission sources of persistent organic pollutants in Karakalpakstan and adjacent regions.

Monitoring and estimating concentrations of polychlorinated biphenyls, dioxins, and furans in cattle milk and soils of Rhine-Delta floodplains.

In the Rhine-Delta, accumulation of microcontaminants in floodplain foodwebs has received little attention in comparison with aquatic communities. Here, soil and cattle milk samples were taken from three floodplains and analyzed for polychlorinated biphenyls (PCBs), dibenzodioxins (PCDDs) and dibenzofurans (PCDFs). Based on 2,3,7, 8-tetrachlorodibenzodioxin equivalents, total PCDD and PCDF residues in milk did not exceed the quality standard of 0.006 microg/kg fat weight. This was still the case if non- and mono-ortho PCBs were added to the total. Yet, the floodplains investigated were only moderately polluted according to previous studies and one cannot exclude higher levels in milk from other floodplains. Bioconcentration ratios of milk fat vs soil organic matter were about 0.01 to 0.1 for persistent PCBs. These values are in accordance with a few literature data found for other persistent compounds. Yet, ratios are lower than expected from equilibrium partitioning. Ratios for PCDDs and PCDFs were even lower, possibly due to biotransformation.