Environmental release and behavior of brominated flame retardants

Recently, environmental problems relating to brominated flame retardants (BFRs) have become a matter of greater concern than ever before, because of the recent marked increase in levels of polybrominated diphenyl ethers (PBDEs) found in human milk in Sweden and North America. The question that arises is whether environmental levels of PBDEs and other BFRs will continue to increase, causing toxic effects to humans. In an attempt to elucidate the current state of the science of BFRs, we review the consumer demand for BFRs (mainly in Japan), the characteristics of waste flame-retarded products, sources of emission, environmental behavior, routes of exposure of humans, temporal trends, and thermal-breakdown products of BFRs. At present, flame-retarded consumer products manufactured 10-20 years ago, when PBDEs were frequently used, are being dumped. The possible major sources of emission of BFRs into the environment are effluent and flue gases from BFR factories and other facilities processing BFRs. With respect to the environmental behavior of BFRs, the lower brominated compounds are, on the whole, predicted to be more volatile, more water soluble, and more bioaccumulative than the higher brominated compounds. The most probable route for exposure of the general human population to PBDEs, especially the lower brominated congeners, is through the diet. The release of BFRs from consumer products treated with these compounds could also lead to human exposure. Temporal trends in PBDE levels in the environment and in humans worldwide seem to vary considerably, depending on the regions or country, with possible reflections of the historic and current use of PBDEs. The environment and the general human population are also exposed to the thermal-breakdown products of PBDEs, such as polybrominated and mixed brominated/chlorinated dibenzo-p-dioxins and dibenzofurans (PBDDs/DFs and mixed PXDDs/DFs).     

Novel brominated flame retardants: a review of their analysis, environmental fate and behaviour

This review summarises current knowledge about production volumes, physico-chemical properties, analysis, environmental occurrence, fate and behaviour and human exposure to the "novel" brominated flame retardants (NBFRs). We define the term NBFRs as relating to BFRs which are new to the market or newly/recently observed in the environment. Restrictions and bans on the use of some polybrominated diphenyl ether (PBDE) formulations, in many jurisdictions, have created a market for the use of NBFRs. To date, most data on NBFRs have arisen as additional information generated by research designed principally to study more "traditional" BFRs, such as PBDEs. This has led to a wide variety of analytical approaches for sample extraction, extract purification and instrumental analysis of NBFRs. An overview of environmental occurrence in abiotic matrices, aquatic biota, terrestrial biota and birds is presented. Evidence concerning the metabolism and absorption of different NBFRs is reviewed. Human exposure to NBFRs via different exposure pathways is discussed, and research gaps related to analysis, environmental sources, fate, and behaviour and human exposure are identified.     

Levels of PCDD/PCDFs and PCBs in edible marine species and human intake: a literature review

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) are lipophilic organic compounds whose origin comes from many different sources. PCDD/Fs and PCBs are ubiquitous and persistent environmental pollutants with a well known potential toxicity, which were included at the 1998 UN-EC POP protocol. Although human exposure to PCDD/Fs and PCBs can occur by various routes, food is the primary source. A number of studies have shown that the major food sources of these organic pollutants are fat-containing animal products, including fish and other seafood. Because of the frequent health recommendations concerning fish consumption, to determine the contribution to the dietary intake of chemical contaminants such as PCDD/Fs and PCBs through fish and other seafood consumption is an issue of special interest. This paper reviews the state of the science regarding recent literature on PCDD/F and PCB levels in marine species and human intake through fish and seafood consumption. The concentrations of these pollutants depend basically on the environment in which the respective species are caught. It is concluded that some groups of population frequently consuming high quantities of certain species could be significantly increasing health risks due to PCDD/F and PCB exposure.     

Metabolism in the toxicokinetics and fate of brominated flame retardants--a review

Several classes of brominated flame retardants (BFRs), namely polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCCD), bis(2,4,6-tribromophenoxy)ethane (BTBPE), and tris(2,3-dibromopropyl)phosphate (Tris), have been identified as environmental contaminants. PBDEs, TBBPA, and HBCCD are of particular concern due to increasing environmental concentrations and their ubiquitous presence in the tissues of humans and wildlife from Europe, Japan, and North America. Regardless, the toxicokinetics, in particular metabolism, of BFRs has received little attention. The present review summarizes the current state of knowledge of BFR metabolism, which is an important factor in determining the bioaccumulation, fate, toxicokinetics, and potential toxicity of BFRs in exposed organisms. Of the minimal metabolism research done, BFRs have been shown to be susceptible to several metabolic processes including oxidative debromination, reductive debromination, oxidative CYP enzyme-mediated biotransformation, and/or Phase II conjugation (glucuronidation and sulfation).However, substantially more research on metabolism is necessary to fully assess BFR fate, uptake and elimination kinetics, metabolic pathways, inter-species differences, the influence of congener structure, and the potential health risks to exposed organisms.     

Determinants of brominated flame retardants in breast milk from a large scale Norwegian study

Brominated flame retardants (BFRs), particularly polybrominated diphenyl ethers (PBDEs), are widely present in human populations. In order to investigate human exposure pathways and associations with socioeconomic and lifestyle factors, 393 breast milk samples from mothers living in various regions throughout Norway were analyzed. Up to ten PBDE congeners were measured in all the samples, hexabromocyclododecane (HBCD) and BDE-209 in subsets of 310 and 46, respectively. The median concentrations of the sum of the seven most prominent PBDEs (BDE-28, 47, 99, 100, 153, 154 and 183), BDE-209 and HBCD were 2.1, 0.32 and 0.86 ng/g lipids, respectively. These concentrations are comparable to the levels generally observed in human populations in Europe. The frequency distributions were quite skewed with long tails towards higher concentrations. Maternal age, parity, education, having a cohabitant employed as electrician, and ventilation were factors significantly associated with some of the BFRs, although these factors only explained a small amount of the variability (R² 0.04–0.16). The mothers' diet was not found to influence the breast milk PBDE and HBCD levels. Our results show that sources other than the diet are important for the variability seen in breast milk BFR concentrations and that exposure from the indoor atmosphere should be emphasized in future studies.     

A review of airborne polycyclic aromatic hydrocarbons (PAHs) and their human health effects

Polycyclic aromatic hydrocarbons (PAHs) are a large group of organic compounds comprised of two or more fused benzene rings arranged in various configurations. PAHs are widespread environmental contaminants formed as a result of incomplete combustion of organic materials such as fossil fuels. The occurrence of PAHs in ambient air is an increasing concern because of their carcinogenicity and mutagenicity. Although emissions and allowable concentrations of PAHs in air are now regulated, the health risk posed by PAH exposure suggests a continuing need for their control through air quality management. In light of the environmental significance of PAH exposure, this review offers an overview of PAH properties, fates, transformations, human exposure, and health effects (acute and chronic) associated with their emission to the atmosphere. Biomarkers of PAH exposure and their significance are also discussed.     

Environmental health impacts of feeding crops to farmed fish

Half of the seafood consumed globally now comes from aquaculture, or farmed seafood. Aquaculture therefore plays an increasingly important role in the global food system, the environment, and human health. Traditionally, aquaculture feed has contained high levels of wild fish, which is unsustainable for ocean ecosystems as demand grows. The aquaculture industry is shifting to crop-based feed ingredients, such as soy, to replace wild fish as a feed source and allow for continued industry growth. This shift fundamentally links seafood production to terrestrial agriculture, and multidisciplinary research is needed to understand the ecological and environmental health implications. We provide basic estimates of the agricultural resource use associated with producing the top five crops used in commercial aquaculture feed. Aquaculture's environmental footprint may now include nutrient and pesticide runoff from industrial crop production, and depending on where and how feed crops are produced, could be indirectly linked to associated negative health outcomes. We summarize key environmental health research on health effects associated with exposure to air, water, and soil contaminated by industrial crop production. Our review also finds that changes in the nutritional content of farmed seafood products due to altered feed composition could impact human nutrition. Based on our literature reviews and estimates of resource use, we present a conceptual framework describing the potential links between increasing use of crop-based ingredients in aquaculture and human health. Additional data and geographic sourcing information for crop-based ingredients are needed to fully assess the environmental health implications of this trend. This is especially critical in the context of a food system that is using both aquatic and terrestrial resources at unsustainable rates.     

Uncertainties in human health risk assessment of environmental contaminants: A review and perspective

Addressing uncertainties in human health risk assessment is a critical issue when evaluating the effects of contaminants on public health. A range of uncertainties exist through the source-to-outcome continuum, including exposure assessment, hazard and risk characterisation. While various strategies have been applied to characterising uncertainty, classical approaches largely rely on how to maximise the available resources. Expert judgement, defaults and tools for characterising quantitative uncertainty attempt to fill the gap between data and regulation requirements. The experiences of researching 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) illustrated uncertainty sources and how to maximise available information to determine uncertainties, and thereby provide an ‘adequate’ protection to contaminant exposure. As regulatory requirements and recurring issues increase, the assessment of complex scenarios involving a large number of chemicals requires more sophisticated tools. Recent advances in exposure and toxicology science provide a large data set for environmental contaminants and public health. In particular, biomonitoring information, in vitro data streams and computational toxicology are the crucial factors in the NexGen risk assessment, as well as uncertainties minimisation. Although in this review we cannot yet predict how the exposure science and modern toxicology will develop in the long-term, current techniques from emerging science can be integrated to improve decision-making.     

A global assessment of phthalates burden and related links to health effects

Phthalates are ubiquitous environmental contaminants which are used in industry as plasticizers and additives in cosmetics. They are classified as Endocrine Disrupting Chemicals (EDCs) which impair the human endocrine system inducing fertility problems, respiratory diseases, childhood obesity and neuropsychological disorders. The aim of this review is to summarize the current state of knowledge on the toxicity that phthalates pose in humans based on human biomonitoring studies conducted over the last decade. Except for conventional biological matrices (such as urine and serum), amniotic fluid, human milk, semen, saliva, sweat, meconium and human hair are also employed for the estimation of exposure and distribution of pollutants in the human body, although data are not enough yet. Children are highly exposed to phthalates relative to adults and in most studies children's daily intake surpasses the maximum reference dose (RfD) set from US Environmental Protection Agency (US EPA). However, the global trend is that human exposure to phthalates is decreasing annually as a result of the strict regulations applied to phthalates.     

A review on human exposure to brominated flame retardants--particularly polybrominated diphenyl ethers

Brominated flame retardants (BFRs) have been and are still heavily used as additive or reactive chemicals in polymers and textiles. Only a few of the BFRs have been assessed in human subjects with a major data set on internal exposures to polybrominated diphenyl ethers (PBDEs). Increasing PBDE levels have been observed in mothers' milk from Sweden as well as in blood from Germany and Norway. The levels are in general lower than PCB levels. However, the PBDE concentrations found in the North Americans are considerably higher compared to European subjects. The PBDEs are dominated by 2,2',4,4'-tetrabromodiphenyl ether (BDE-47). Decabromodiphenyl ether (BDE-209) is reported both in the general population and in occupationally exposed persons showing the bioavailability of this high molecular weight compound. While the lower and medium brominated diphenyl ethers are persistent, BDE-209 has a fairly short half-life of approximately 2 weeks. Tetrabromobisphenol A (TBBPA) is readily eliminated in humans showing a half-life of about 2 days. Still, TBBPA is accumulated in humans but a continuous exposure to this BFR is required to maintain a certain level in the human subject. TBBPA has not been detected in the general population but in people exposed at work. The current review addresses human exposure routes and levels of BFRs.     

Toxic effects of brominated flame retardants in man and in wildlife

Brominated flame retardants (BFRs) are ubiquitous industrial chemicals, and many of them are produced in large volumes. Due to this fact, several BFRs are found in quantifiable levels in wildlife, as well as in humans. However, we are still lacking information on the effects of BFR in wildlife and, especially, in man. This review summarises the biological effects of polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA) and derivates, hexabromocyclododecane (HBCD) and polybrominated biphenyls (PBBs), however excluding other aspects such as environmental levels. These BFR groups were selected because of a large volume production (PBDEs, TBBPA and derivates), and availability of some toxicity data in spite of much lower production volumes (HBCD and PBBs). In addition, the increase in levels of PBDEs in human (breast milk) and wildlife samples during later time made it especially interesting to include this BFR group. PBDES: The commercial PBDE products predominantly consist of so-called penta-, octa- and decabromodiphenyl ether products. Each product consists of a rather narrow range of congeners and is named after the dominating congener as regards the bromination pattern. Generally, the PentaBDEs seem to cause adverse effects at the comparably lowest dose, whereas much higher doses were needed for effects of the DecaBDEs. The critical effects of PentaBDEs are those on neurobehavioural development (from 0.6 mg/kg body weight) and, at somewhat higher dose, thyroid hormone levels in rats and mice, of OctaBDEs on fetal toxicity/teratogenicity in rats and rabbits (from 2 mg/kg body weight), and of DecaBDEs on thyroid, liver and kidney morphology in adult animals (from 80 mg/kg body weight). Carcinogenicity studies, only performed for DecaBDEs, show some effects at very high levels, and IARC (1990) evaluates DecaBDEs not classifiable as to its carcinogenicity to humans. TBBPA: The toxicity of TBBPA in the experimental in vivo studies is suggested to be low. In most reported studies, only doses in g/kg body weight were effective, but at least one study suggested renal effects at around 250 mg/kg body weight. Although difficult to include and interpret in a quantitative risk assessment, the in vitro effects on immunological and thyroid hormones, as well as binding to erythrocytes should be noted. Before a solid standpoint could be reached on TBBPA toxicity additional studies must be performed. This statement is even more valid regarding the TBBPA derivates, where there is an almost complete lack of toxicity data. HBCD: Also in the case of HBCD, relevant toxicity studies are lacking. Based on the present animal studies, a critical effect is seen in the liver and on thyroid hormones (LOAEL 100 mg/kg body weight/day). However, in a recent short paper behavioural effects in mice pups were observed already at 0.9 mg/kg body weight, and behavioural effects may be a sensitive endpoint for HBCD, as well as for other BFRs. PBBS: Due to the Michigan accident in 1973-1974, many toxicity studies on PBBs are available. The critical experimental effects are those on reproduction and carcinogenicity, and a NOAEL of 0.15 mg/kg body weight/day could be suggested based on the cancer effects. In man no unequivocal effects have been observed, although in some studies neurological and musculoskeletal symptoms were suggested. Based on the carcinogenic effects in animals, a human TDI of 0.15 microg/kg body weight has been presented.To conclude, the toxicity data are almost entirely based on experimental models. There are differences among the BFR groups, as well as within these groups, both regarding type of toxic effect and at what dose it appears. As BFRs will continue to appear both in industrial applications and, even if the production has ceased, in our environment, there is a continued need for effects studies on BFRs.     

Applying radioecology in a world of multiple contaminants

This paper presents a review of the current status of radioecology and how it might be applied to contribute to a broader range of environmental pollution and contamination problems. In many respects radioecology is a unique and specialised branch of environmental science. However, radioecologists could be much more aware of the similarities and differences between their field and other fields of environmental pollution science. Areas of common interest described herein are exposure and risk assessment, and the problem of the bioavailability of potentially toxic substances in environmental media. It is concluded that radiometric methods and radioecological modelling methods can assist significantly with understanding and quantifying both these issues. The existence of multiple contaminants at many locations around the world dictates that assessment and remediation exercises should be carried out in an integrated fashion, as a partnership between scientific disciplines.     

Environmental occurrence,analysis and human exposure to the flame retardant tetrabromobisphenol-A (TBBP-A)-A review

TBBP-A is a high production volume chemical applied widely as a flame retardant in printed circuit boards. Recent studies have raised concern over potential harmful implications of TBBP-A exposure in human and wildlife, leading to its classification under group 2A “Probably carcinogenic to humans” by the International Agency for Research on Cancer. This article provides a comprehensive review of the available literature on TBBP-A analysis, environmental levels and human exposure. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been identified as the method of choice for robust, accurate and sensitive analysis of TBBP-A in different matrices. TBBP-A has been detected in almost all environmental compartments all over the world, rendering it a ubiquitous contaminant. Human exposure studies revealed dust ingestion and diet as the major pathways of TBBP-A exposure in the general population. Toddlers are likely to be more exposed than adults via accidental indoor dust ingestion. Moreover, exposure to TBBP-A may occur prenatally and via breast milk. There are no current restrictions on the production of TBBP-A in the EU or worldwide. However, more research is required to characterise human exposure to TBBP-A in and around production facilities, as well as in e-waste recycling regions.     

Are brominated flame retardants endocrine disruptors?

Brominated flame retardants (BFRs) are a group of compounds that have received much attention recently due to their similarity with "old" classes of organohalogenated compounds such as polychlorinated biphenyls (PCBs), in terms of their fate, stability in the environment and accumulation in humans and wildlife. Toxic effects, including teratogenicity, carcinogenicity and neurotoxicity, have been observed for some BFR congeners, in particular the brominated diphenyl ethers (BDEs). This concise review focuses on the potency of BFRs and to disrupt endocrine systems, and attempts to answer the question whether or not BFRs are endocrine disruptors. Evidence is provided on the disruption of the thyroid hormone system by BFRs, with particular emphasis on the BDEs, as most recent data is available on this class of flame retardants. Similar to the hydroxylated PCBs, in vitro mechanistic studies as well as animal experiments have demonstrated the effects of BDEs on thyroid hormone transport and metabolism. An overview of possible effects of BFRs on the estrogen system is also provided. Research gaps are outlined, as well as ongoing and future studies in the European community aimed at contributing to comprehensive risk assessments based on the endocrine-disrupting effects of BFRs.     

Antibiotics in the aquatic environments: A review of the European scenario

The discovery of antibiotics is considered one of the most significant scientific achievements of the 20th century, revolutionizing both human and veterinary medicine. However, antibiotics have been recently recognized as an emerging class of environmental contaminants since they have been massively administrated in humans and animals and persist in the environment through a complex vicious cycle of transformation and bioaccumulation. The diffusion of antibiotics in the environment, particularly in natural water systems, contributes to the development and global dissemination of antibiotic resistance. This phenomenon is one of the most important challenges to the health care sector in the 21st century. As a result, studies on the occurrence, fate, and effects of antibiotics in European aqueous environments have increased in the last years. Nevertheless, their potential aquatic ecotoxicity and human toxicity via environmental exposure routes remain unknown. Consequently, antibiotics are not regulated through the current European environmental water quality standards, which requires evidence concerning their widespread environmental contamination and intrinsic hazard. In this context, this literature review summarizes the state of knowledge on the occurrence of antibiotics in the different aqueous environmental systems across the Europe, as reported since 2000. Relating this subject to antibiotic consumption and their dynamic behavior in the environment, the acquired insights provide an improved understanding on aquatic pollution by antibiotics to outline the European scenario. Moreover, it addresses challenges, prospects for future research, and typical topics to stimulate discussion.     

Human exposure to PCDDs, PCDFs and dioxin-like PCBs associated with seafood consumption in Korea from 2005 to 2007

Concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DLPCBs) were measured in 26 seafoods commonly consumed by the Korean population. The total toxic equivalent (TEQ) concentrations in seafood samples ranged from 0.01 to 6.76 pg TEQ/g wet wt, which were comparable with those found in other countries. The predominant congeners found in seafood samples were 2, 3, 4, 7, 8-PeCDF and 2, 3, 7, 8-TCDF for PCDD/Fs and PCB 118 for DLPCBs. Dietary intakes of PCDD/Fs and DLPCBs from seafood consumption were estimated for various age groups and gender in Korea. The dietary intake of PCDD/Fs and DLPCBs from seafood consumption for the general population was estimated to be 1.23 pg TEQ/kg bw/day, values that are in the range of those reported for other countries. Mackerel, tuna and hairtail contributed to the highest TEQ intakes, which collectively accounted for 66% of the total intake. Among the eight age groups investigated, 3-6 year old children had the highest TEQ exposure, followed by 50-64 years, 30-39 years and <2 years. Considering contributions of seafood consumption to the total dietary intake studies, the dietary TEQ intakes to the general population appear to be below the threshold values by international organizations. The present study may be useful for risk management for dioxins and dioxin-like contaminants in Korean seafood.     

Chemical contaminants in feedlot wastes: concentrations, effects and attenuation

Commercial feedlots for beef cattle finishing are potential sources of a range of trace chemicals which have human health or environmental significance. To ensure adequate protection of human and environmental health from exposure to these chemicals, the application of effective manure and effluent management practices is warranted. The Australian meat and livestock industry has adopted a proactive approach to the identification of best management practices. Accordingly, this review was undertaken to identify key chemical species that may require consideration in the development of guidelines for feedlot manure and effluent management practices in Australia. Important classes of trace chemicals identified include steroidal hormones, antibiotics, ectoparasiticides, mycotoxins, heavy metals and dioxins. These are described in terms of their likely sources, expected concentrations and public health or environmental significance based on international data and research. Androgenic hormones such as testosterone and trenbolone are significantly active in feedlot wastes, but they are poorly understood in terms of fate and environmental implications. The careful management of residues of antibiotics including virginiamycin, tylosin and oxytetracycline appears prudent in terms of minimising the risk of potential public health impacts from resistant strains of bacteria. Good management of ectoparasiticides including synthetic pyrethroids, macrocyclic lactones, fluazuron, and amitraz is important for the prevention of potential ecological implications, particularly towards dung beetles. Very few of these individual chemical contaminants have been thoroughly investigated in terms of concentrations, effects and attenuation in Australian feedlot wastes.     

Irish fish, Irish people: roles and responsibilities for an emptying ocean

Human decisions shape patterns of seafood resource use. Consequently, it is also these decisions made by actors within seafood industries which ultimately determine the environmental impact of fisheries resource extraction from marine environments. In this study, we investigated the roles and influences of various actors within the Irish seafood industry. Our objectives were to learn more about the working dynamics of the industry and identify possibilities for improvements towards industry sustainability. We employed qualitative research methods including semi-structured interviews, focus groups and participant observation to access information from Irish consumers, retailers, wholesalers, scientists and key industry informants. The diversity of seafood products available within the Irish market is generally low. However, consumers who experiment with trying new varieties of seafood are influenced by dining experiences at restaurants or while travelling abroad as well as through cooking shows or cookbooks. Potential for influence on factors including consumer choice, stocking and sourcing decisions, business management and fisheries policy was found within all levels of the seafood industry, though a sense of responsibility in the context of seafood sustainability was less common. In addition, the absence of shortages within the Irish market due to imports, aquaculture and mislabelling appears to be preventing widespread acceptance about claims of overfishing. It is clear that ultimately, responsible policy decisions and effective enforcement will be needed to improve the overall sustainability of the industry. However, pressure for positive change can come from all actors that prioritise sustainability as the most important objective for future industry operation.     

Evaluation of 3D-human skin equivalents for assessment of human dermal absorption of some brominated flame retardants

Ethical and technical difficulties inherent to studies in human tissues are impeding assessment of the dermal bioavailability of brominated flame retardants (BFRs). This is further complicated by increasing restrictions on the use of animals in toxicity testing, and the uncertainties associated with extrapolating data from animal studies to humans due to inter-species variations. To overcome these difficulties, we evaluate 3D-human skin equivalents (3D-HSE) as a novel in vitro alternative to human and animal testing for assessment of dermal absorption of BFRs. The percutaneous penetration of hexabromocyclododecanes (HBCD) and tetrabromobisphenol-A (TBBP-A) through two commercially available 3D-HSE models was studied and compared to data obtained for human ex vivo skin according to a standard protocol. No statistically significant differences were observed between the results obtained using 3D-HSE and human ex vivo skin at two exposure levels. The absorbed dose was low (less than 7%) and was significantly correlated with log K_ow of the tested BFR. Permeability coefficient values showed increasing dermal resistance to the penetration of γ-HBCD > β-HBCD > α-HBCD > TBBPA. The estimated long lag times (> 30 min) suggests that frequent hand washing may reduce human exposure to HBCDs and TBBPA via dermal contact.     

Disruption of retinoid transport, metabolism and signaling by environmental pollutants

Although the assessment of circulatory levels of retinoids has become a widely used biomarker of exposure to environmental pollutants, the adverse effects caused by imbalance of the retinoid metabolism and signaling in wildlife are not known in detail. Retinoids play an important role in controlling such vital processes as morphogenesis, development, reproduction or apoptosis. Unlike other signaling molecules, retinoids are not strictly endogenous but they are derived from dietary sources of vitamin A or its precursors and thus they are sometimes referred to as 'dietary' hormones. Some environmental pollutants that affect embryogenesis, immunity or epithelial functions were also shown to interfere with retinoid metabolism and signaling in animals. This suggests that at least some of their toxic effects may be related to interaction with the retinoid metabolism, transport or signal transduction. This review summarizes in vivo and in vitro studies on interaction of environmental complex samples, pesticides, polychlorinated dioxins, polychlorinated biphenyls, polycyclic aromatic compounds and other organic pollutants with physiology of retinoids. It sums up contemporary knowledge about levels of interaction and mechanisms of action of the environmental contaminants.