Chemical Similarity and Threshold of Toxicological Concern (TTC) Approaches: Report of an ECB Workshop held in Ispra, November 2005

There are many national, regional and international programmes – either regulatory or voluntary – to assess the hazards or risks of chemical substances to humans and the environment. The first step in making a hazard assessment of a chemical is to ensure that there is adequate information on each of the endpoints. If adequate information is not available then additional data is needed to complete the dataset for this substance. For reasons of resources and animal welfare, it is important to limit the number of tests that have to be conducted, where this is scientifically justifiable. One approach is to consider closely related chemicals as a group, or chemical category, rather than as individual chemicals. In a category approach, data for chemicals and endpoints that have been already tested are used to estimate the hazard for untested chemicals and endpoints. Categories of chemicals are selected on the basis of similarities in biological activity which is associated with a common underlying mechanism of action. A homologous series of chemicals exhibiting a coherent trend in biological activity can be rationalised on the basis of a constant change in structure. This type of grouping is relatively straightforward. The challenge lies in identifying the relevant chemical structural and physicochemical characteristics that enable more sophisticated groupings to be made on the basis of similarity in biological activity and hence purported mechanism of action. Linking two chemicals together and rationalising their similarity with reference to one or more endpoints has been very much carried out on an ad hoc basis. Even with larger groups, the process and approach is ad hoc and based on expert judgement. There still appears to be very little guidance about the tools and approaches for grouping chemicals systematically. In November 2005, the ECB Workshop on Chemical Similarity and Thresholds of Toxicological Concern (TTC) Approaches was convened to identify the available approaches that currently exist to encode similarity and how these can be used to facilitate the grouping of chemicals. This report aims to capture the main themes that were discussed. In particular, it outlines a number of different approaches that can facilitate the formation of chemical groupings in terms of the context under consideration and the likely information that would be required. Grouping methods were divided into one of four classes – knowledge-based, analogue-based, unsupervised, and supervised. A flowchart was constructed to attempt to capture a possible work flow to highlight where and how these approaches might be best applied.JRC.I.3-Toxicology and chemical substance

Phthalate Diesters and Their Metabolites in Human Breast Milk, Blood or Serum, and Urine as Biomarkers of Exposure in Vulnerable Populations

BACKGROUND: Phthalates may pose a risk for perinatal developmental effects. An important question relates to the choice of suitable biological matrices for assessing exposure during this period. OBJECTIVES: This study was designed to measure the concentrations of phthalate diesters or their metabolites in breast milk, blood or serum, and urine and to evaluate their suitability for assessing perinatal exposure to phthalates. METHODS: In 2001, 2-3 weeks after delivery, 42 Swedish primipara provided breast milk, blood, and urine samples at home. Special care was taken to minimize contamination with phthalates (e.g., use of a special breast milk pump, heat treatment of glassware and needles, addition of phosphoric acid). RESULTS: Phthalate diesters and metabolites in milk and blood or serum, if detected, were present at concentrations close to the limit of detection. By contrast, most phthalate metabolites were detectable in urine at concentrations comparable to those from the general population in the United States and in Germany. No correlations existed between urine concentrations and those found in milk or blood/serum for single phthalate metabolites. Our data are at odds with a previous study documenting frequent detection and comparatively high concentrations of phthalate metabolites in Finnish and Danish mothers' milk. CONCLUSIONS: Concentrations of phthalate metabolites in urine are more informative than those in milk or serum. Furthermore, collection of milk or blood may be associated with discomfort and potential technical problems such as contamination (unless oxidative metabolites are measured). Although urine is a suitable matrix for health-related phthalate monitoring, urinary concentrations in nursing mothers cannot be used to estimate exposure to phthalates through milk ingestion by breast-fed infants

Exposure based waiving and triggering of tests within REACH : A discussion paper within the Nordic projects on Information Strategies (NOIS)

The main objective with this work was to discuss and give guidance on when testing according to REACH may be omitted based on information on exposure. This includes interpretation of the terminology used for the specific exposure based waiving according to Column 2 of Annexes VIII-X in REACH and the general exposure based waiving according to Annex XI. In addition, it includes exposure based triggering of testing. Waiving of testing is considered to be risk-based rather than exposure-based. One issue with risk-based waiving is that the toxicological study under discussion for waiving is sometimes needed in order to decide whether the exposure is negligible. In order to waive testing it is necessary with detailed and extensive knowledge on exposure over the whole life-cycle. Information corresponding to an exposure scenario is needed even though this is only requested if the substance is a PBT eller vPvB or fulfils the criteria for classification

Benchmark dose for cadmium-induced renal effects in humans

OBJECTIVES: Our goal in this study was to explore the use of a hybrid approach to calculate benchmark doses (BMDs) and their 95% lower confidence bounds (BMDLs) for renal effects of cadmium in a population with low environmental exposure. METHODS: Morning urine and blood samples were collected from 820 Swedish women 53-64 years of age. We measured urinary cadmium (U-Cd) and tubular effect markers [N-acetyl-beta-D-glucosaminidase (NAG) and human complex-forming protein (protein HQ in 790 women and estimated glomerular filtration rate (GFR; based on serum cystatin Q in 700 women. Age, body mass index, use of nonsteroidal anti-inflammatory drugs, and blood lead levels were used as covariates for estimated GFR. BMDs/BMDLs corresponding to an additional risk (benchmark response) of 5 or 10% were calculated (the background risk at zero exposure was set to 5%). The results were compared with the estimated critical concentrations obtained by applying logistic models used in previous studies on the present data. RESULTS: For both NAG and protein HC, the BMDs (BMDLs) of U-Cd were 0.5-1.1 (0.4-0.8) mu g/L (adjusted for specific gravity of 1.015 g/mL) and 0.6-1.1 (0.5-0.8) mu g/g creatinine. For estimated GFR, the BMDs (BMDLs) were 0.8-1.3 (0.5-0.9) mu g/L adjusted for specific gravity and 1.1-1.8 (0.7-1.2) mu g/g creatinine. CONCLUSION: The obtained benchmark doses of U-Cd were lower than the critical concentrations previously reported. The critical dose level for glomerular effects was only slightly higher than that for tubular effects. We suggest that the hybrid approach is more appropriate for estimation of the critical U-Cd concentration, because the choice of cutoff values in logistic models largely influenced the obtained critical U-Cd

Quantitative and statistical analysis of differences in sensitivity between Long-Evans and Han/Wistar rats following long-term exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin

Historically, quantitative health risk assessment of chemical substances is based on deterministic approaches. For a more realistic and informative health risk assessment, however, the variability and uncertainty inherent in measurements should be taken into consideration. The variability and uncertainty may be assessed by applying probabilistic methods when performing dose-response assessment, exposure assessment and risk characterization. The benchmark dose (BMD) method has been suggested as an alternative to the no observed (adverse) effect level (NO(A)EL) approach in dose-response assessment of non-cancer health effects. In contrast to the NO(A)EL that is limited to being one of the experimental dose levels, the BMD is estimated as the dose corresponding to a predetermined change in response, according to a model fitted to the dose-response data. In the present thesis, quantitative differences in sensitivity between dioxin sensitive Long- Evans (L-E) and dioxin resistant Han/Wistar (H/W) rats following long-term exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was investigated. Sensitivity differences were analyzed by comparing BMDs for the two strains, considering a number of conventional toxicological endpoints, endpoints relevant for the endocrine system, and a group of bone parameters. Differences between the strains were most pronounced for hepatic foci; L-E rats were approximately 20-40 times more sensitive than H/W rats. For body and organ weight parameters, L-E rats were 10-20 times more sensitive than H/W rats. For retinoid parameters and hepatic CYP1A1 induction, estimated differences between the strains were generally about 5-fold. For bone effects, significant strain differences were observed with the L-E rat being the most sensitive strain. This difference was most pronounced (about 49-fold) for cross-sectional area of proximal tibia. It was also concluded that the BMD approach is a more suitable method for evaluation of bone parameters compare to the NOAEL approach. In another application, relative potency values (REPs) were established for a group of dioxinlike (DL) and non-dioxin-like (NDL) polychlorinated biphenyl (PCB) congeners as the ratio between BMDs, median effective doses (ED50s), or NOELs. This analysis was based on increased liver weight, decreased hepatic vitamin A levels, and increased hepatic EROD activity. The findings indicated that the BMD approach results in more reliable REP values compared to the ED50 and NOEL approaches. The BMD approach also provides more information about the precision of the estimated REP values by the calculation of a two-sided 90% confidence interval; a confidence interval may also be established for a ED50 ratio but not for a NO(A)EL ratio. Overall findings in this analysis supported further development and use of endpoint specific systems for assessment of human exposure to mixtures of chemicals with similar as well as different mode-of-actions. Finally, the potential health impact of a group of PCBs was characterized by estimating the cumulative margins of exposure (MOEs) for the adult Swedish population. A cumulative MOE distribution was quantified by simultaneous integration of a reference dose (RfD) distribution and a distribution for the human dietary exposure. Both a relative potency factor (RPF) based approach and an RPF-free approach were used for estimating the cumulative MOE. Results indicated that the cumulative MOE could be up to four times lower for women compared to men. The cumulative MOE reflected the MOE for PCB 126; other PCB congeners had little contribution. Compared to conventional MOE approaches, the newer approaches considered herein provide an improved tool under which potential health concerns can be assessed by accounting for both variability and various uncertainties, quantitatively, contributing to improving cumulative health risk assessments for the human population

Phthalates and their metabolites in human breast milk, blood and urine as measures for monitoring exposure in human risk groups

För att undersöka halter av ftalater i svenskar och vilken matris som bäst lämpar sig för hälsorelaterad miljöövervakning har ftalater och ftalatmetaboliter analyserats i en grupp kvinnor som nyligen fött barn. I samband med förlossning på Universitetssjukhuset i Lund tillfrågades förstföderskor om medverkan och 42 kvinnor kom att ingå i studien. När barnet var 2-3 veckor gammalt pumpade mamman ut 50 mL bröstmjölk. Blod- och urinprov togs en vecka senare. Omfattande förändringar av standardmetoder för provtagning av mjölk och blod gjordes för att minimera risken för kontaminering av proverna. För mjölkprovtagningen användes en specialkonstruerad manuell pump av polykarbonat med ftalatfri packning. Blodprov togs med hjälp av endast kanyl och provrör (eftersom propparna i vaccutainrör innehåller ftalater). Proverna förvarades i värmebehandlade glasbehållare och fosforsyra tillsattes för att motverka metabolism av ftalater i mjölk- och blodprover. Analyserna av bröstmjölk visade värden nära eller under detektionsgränsen (LOD) för flertalet ftalater eller deras metaboliter. Även i blod och serum var nivåerna vanligtvis nära eller under LOD. I urin analyserades endast metaboliter och dessa kunde kvantifieras i 53-100 % av proverna. Nivåerna av ftalatmetaboliter i urin hos de svenska kvinnorna var i paritet med nivåerna hos en allmänbefolkning i USA och Tyskland. Några klara korrelationer mellan nivåer i t ex urin och bröstmjölk respektive blod påvisades inte. Resultaten av studien anger att för närvarande är analys av ftalatmetaboliter i urin den mest framkomliga vägen för skattning av ftalatexponering hos människa. Provtagning och analys av mjölk och blod innebar betydligt större svårigheter. Framför allt framstår risken för kontaminering vid provtagning som betydande och en stor del av ftalaterna och dess metaboliter uppvisade låga halter, vid eller under LOD. Dessutom kan ftalater brytas ned i blod och mjölk. I flertalet internationella publicerade studier av ftalatexponering används urinmetabolit-analyser som ett mått på exponering för ftalater. I en nyligen publicerad amerikansk studie av ett 80-tal nyfödda pojkar sågs ett samband mellan kort ano-genitalt avstånd och nivåer av ftalatmetaboliter i urin hos deras mammor under graviditeten. Den amerikanska studien behöver bekräftas, men metaboliterna var desamma som i vår studie och en jämförelse visar att mediannivåerna var lägre för vissa men högre för andra metaboliter. Vår studie indikerar att svenska kvinnor i fertil ålder inte sällan exponeras för ftalater i nivåer som satts i samband med fosterpåverkan