Modeling toxic endpoints for improving human health risk assessment of polycyclic aromatic hydrocarbons – parent compounds and simple mixtures

Risk assessments for mixtures of polycyclic aromatic hydrocarbons (PAH) are problematic due to the lack of available potency and toxicity data on individual compounds and mixtures. This article examines the toxicity of parent compounds and designed mixtures of PAH in order to bridge the gap between component assessment and mixture assessment for this class of ubiquitous compounds. The objective for this study was to test seven parent PAH compounds and four PAH mixtures in a set of three bioassays to evaluate the toxicity of parent compound PAH and binary mixtures of PAH. PAH and mixtures were examined in the Salmonella/microsome mutagenicity assay, a Gap Junction Intercellular Communication assay, and the 7-ethoxyresorufin-O-deethylase assay. These assays were chosen for their ability to measure specific toxic endpoints related to the carcinogenic process (i.e. initiation, promotion, and progression). Two compounds similar in structure, benzo(a) pyrene (BAP) and benzanthracene, consistently produced positive results in all three bioassays. Conversely, a linear PAH, anthracene, produced negative results in all three bioassays. An antagonistic response was observed for the mixtures in all three bioassays. Chemical structure was important in explaining the observed responses. Using chemical structure–activity relationships with the steps of the carcinogenic process may be used to improve estimates of toxicity for compounds and mixtures for human health risk assessments.     

Evaluation of an Exposure Assay to Measure Uptake of Sediment Pah by Fish

The ecological risks of polynuclear aromatic hydrocarbons (PAH) in aquatic sediments will vary with both toxicity and bioavailability to aquatic biota. While there are standardized protocols to test the acute toxicity of sediment-borne compounds to aquatic invertebrates, there are none for assessing bioavailability to fish. We found that sediment-borne PAH caused an exposure-dependent induction of cytochrome P450 (CYP1A) enzymes in rainbow trout (Oncorhynchus mykiss) fingerlings exposed in semi-static 96 h bioassays, as shown by increased activity of ethoxyresorufin-o-deethylase (EROD). Assuming that PAH are taken up by trout due to partitioning from organic and inorganic constituents of sediments, we tested the effect of different test variables on bioaccumulation using induction as an index of exposure. EROD activity increased with exposure of fish to increasing volumes of sediments containing PAH, i.e., with increasing ratios of sediment to water. Uptake of single compounds from sandy sediments did not differ from uptake from clay or low organic (7% LOI — loss on ignition) sediments, but decreased when organic content was very high (58% LOI). Maximum induction was observed within 24~h of exposure and at 7.5^C relative to 15, 22, or 28^C. Storage and handling techniques had minor effects on sediment EROD induction potency. Absolute EROD activity was greater in white sucker (Catostomus commersoni) a benthic species, than in trout, a pelagic species. However, when basal (negative control) activity was accounted for, there was no difference in response between the species. Together, these experiments provide a basis for developing a standard protocol to test the bioavailability to fish of sediment-borne PAH.     

Polycyclic aromatic hydrocarbons (PAH) in different forest humus types

The behavior of 20 PAH in the organic layers of a L mull, an Of mull and a mor was assessed by a combined approach of a soil profile study, and the analysis of particle-size separates. Increasing PAH concentrations with depth in the mor profile (L, 866 μg kg⁻³; Of, 2902 μg kg⁻¹; Oh, 10489 ug kg⁻¹) were assigned to selective enrichment during organic matter decomposition. PAH were further highly enriched within the finer separates. For the L horizons, significant positive correlations were established between the enrichment of individual PAH (as observed from the decomposition gradient between the >2-mm fraction and the < 0.05-mm fraction), and the K_OW for each compound. The slope of the regression line, m, described the degree of differentiation between low- and high-molecular PAH during litter decomposition. Since m was greatest in the most biologically active humus type (L mull, 0.33) and smallest in the most inactive (mor, 0.20), microbial breakdown was assumed as the dominating process for this differentiation. The results also indicated that decomposition processes had already taken place in the L horizons, leading to morphological and chemical changes of organic matter, and to an enrichment of high molecular PAH.     

DOC和CDPF对柴油公交车颗粒物组分影响

以一辆柴油公交车为试验样车,在重型底盘测功机上运行中国典型城市公交循环(CCBC),收集尾气颗粒物以分析柴油车安装不同后处理装置的颗粒物组分排放特性.结果表明,原机颗粒物总碳组分中元素碳(EC)比有机碳(OC)多,测得有机组分中,脂肪酸占60.9%,直链烷烃占32.4%,藿烷和PAHs较少.脂肪酸主要是C16:0,C18、C14和C18:1也较多,直链烷烃主要分布于C18~C24,C21H44和C22H46最多.PAHs质量排放以中小分子量为主,Pyr最多,FL和PA也较多,毒性则以中高分子量为主,Ba P毒性最强,B(b+k)F、Ba A以及Icd P也是主要毒性组分.DOC后PAHs总毒性降低2.7%,不同CDPF后总毒性进一步降低89.6%~93.8%.DOC和CDPF对总碳组分的减排率分别为18.9%和70.5%~72.5%,但对不同组分的减排效果差别较大,不同贵金属负载量的CDPF对各组分减排效果无明显影响.     

Maximum permissible and negligible concentrations for some organic substances and pesticides

The aim of the paper is to provide interested parties the methods that were used for generic hazard assessment in The Netherlands, and the resulting so-called maximum permissible concentrations (MPCs) and the negligible concentrations (NCs) for approximately 150 organic substances and pesticides. The MPCs and NCs were derived for water, sediment, and soil. The concentration in the environment above which the risk of adverse effects was considered unacceptable to ecosystems is called the MPC. The MPCs take into account that the substances are distributed among the different environmental compartments, and are harmonized accordingly. The MPCs served as a basis for the Dutch government to set generic environmental quality standards (EQS) in The Netherlands (IWINS,[15]). EQS in turn are used by the Dutch Government to assess the environmental quality and for other environmental policy purposes. Concentrations in the environment below which the occurrence of adverse effects is considered to be negligible are called NCs. Hazards must be reduced when the environmental concentration of a substance exceeds its MPC. In-between this limits reduction of hazards is preferable. The MPC is a scientifically derived hazard limit. The NC is simply defined as 1% of the MPC. In general, there is a great demand for ecotoxicological data that currently limits a more reliable estimate of many MPCs. For water, approximately half of the MPCs are derived on the basis of four or more NOECs (no observed effect concentrations). For the other half, MPCs are based on only a few chronic or acute tests. For soil and sediment, however, almost no ecotoxicological data are available, and MPCs for those compartments have, in many cases, been derived from MPCs in water applying the equilibrium partitioning method (EqP-method), resulting in MPCs with greater uncertainty. Some of the methods and underlying assumptions that have been used may need improvement. For example, the factor between MPC and NC, the statistical extrapolation method, the method that is used for secondary poisoning, the role of the background concentrations of ‘naturally’ occurring substances, and the bioavailability and the EqP-method. There is a great need for hazard limits, and the present compilation tries to provide those as well as identifying research gaps.     

The variation of street air levels of PAH and other mutagenic PAC in relation to regulations of traffic emissions and the impact of atmospheric processes

The occurrence of particle associated PAH and other mutagenic PAC was determined in 1996 in the street air of Copenhagen. In addition, particle extracts were tested for mutagenicity. The measurements were compared with previous measurements in 1992/1993. The levels had decreased in this period. The decrease was caused by an implementation of light diesel fuels for buses and the exchange of older petrol-driven passenger cars with catalystequipped new ones. About 65% of the reduction was caused by the application of the light diesel fuels. Under special conditions, chemical processes in the atmosphere produced many more mutagens than the direct emissions. The concentrations of S-PAC and N-PAC were 10 times lower than those of PAH, while the levels of oxy-PAH were in the same order of magnitude as those of PAH. Benzanthrone, an oxy-PAH, is proposed to be formed in the atmosphere in addition to direct emissions. Benzo(a)pyrene, often applied as an air quality criteria indicator, was photochemically degraded in the atmosphere. A strong increase in the mutagenic activities was observed to coincide with a depletion of benzo(a)pyrene.     

广州市气溶胶中多环芳烃分布、季节性变化及来源判识指标

多环芳烃（PAH）具致癌特性,研究气溶胶中的PAH在不同功能区中的分布、变化及来源,具有重要意义。使用大流量总悬浮颗粒采样器,在广州市区5个代表性功能区采集季节性气溶胶样品共25个。用GC-FID、GC-MSD定量和半定量分析PAH组份。研究区气溶胶中检测出23种母核PAH,50多种烷基PAH。优先控制的PAH含量随功能区和季节而变化,其秋、夏季平均浓度具工业区＞商业区＞交通区＞化工区的分布特征,秋季优控PAH浓度高于春、夏季。根据荧蒽／芘和间四联苯／荧蒽比值等指标判别,区内PAH主要来源于油、煤类等燃料的不完全燃烧。