The histone acetyltransferase HBO1 promotes efficient tip cell sprouting during angiogenesis.

Blood vessel growth and remodelling are essential during embryonic development and disease pathogenesis. The diversity of endothelial cells (ECs) is transcriptionally evident and ECs undergo dynamic changes in gene expression during vessel growth and remodelling. Here, we investigated the role of the histone acetyltransferase HBO1 (KAT7), which is important for activating genes during development and for histone H3 lysine 14 acetylation (H3K14ac). Loss of HBO1 and H3K14ac impaired developmental sprouting angiogenesis and reduced pathological EC overgrowth in the retinal endothelium. Single-cell RNA sequencing of retinal ECs revealed an increased abundance of tip cells in Hbo1-deficient retinas, which led to EC overcrowding in the retinal sprouting front and prevented efficient tip cell migration. We found that H3K14ac was highly abundant in the endothelial genome in both intra- and intergenic regions, suggesting that HBO1 acts as a genome organiser that promotes efficient tip cell behaviour necessary for sprouting angiogenesis. This article has an associated 'The people behind the papers' interview.

Progression of diabetic retinopathy in women with pregestational diabetes during pregnancy and postpartum.

BACKGROUND: Diabetic retinopathy (DR) may worsen during pregnancy, but its course in the postpartum remains poorly understood. Understanding the natural history of DR during and after pregnancy can help determine when sight-threatening DR treatment should be administered. METHODS: A prospective longitudinal cohort study recruited pregnant women with pre-existing type 1 (T1D) or type 2 diabetes from two tertiary Diabetes Antenatal Clinics in Melbourne, Australia. Eye examination results in early pregnancy, late pregnancy, and up to 12-months postpartum were compared to determine DR changes. Two-field fundus photographs and optical coherence tomography scans were used to assess DR severity. RESULTS: Overall, 105 (61.4%) women had at least two eye examinations during the observation period. Mean age was 33.5 years (range 19-51); 54 women (51.4%) had T1D; 63% had HbA1c <7% in early pregnancy. DR progression rate was 23.8% (95% CI 16.4-32.6). Having T1D (RR 4.96, 95% CI 1.83-13.46), pre-existing DR in either eye (RR 4.54, 95% CI 2.39-8.61), and elevated systolic blood pressure (adjusted RR 2.49, 95% CI 1.10-5.66) were associated with increased risk of progression. Sight-threatening progression was observed in 9.5% of women. Among the 19 eyes with progression during pregnancy, 15 eyes remained stable, three eyes progressed, and only one eye regressed in the postpartum. CONCLUSIONS: Nearly 1 in 4 women had DR progression from conception through to 12-months postpartum; almost half of these developing sight-threatening disease. DR progression occurring during pregnancy was found to predominantly remain unchanged, or worsen, after delivery, with very few eyes spontaneously improving postpartum.

Impact of Microplastics on the Ocular Surface.

Plastics are synthetic materials made from organic polymers that are ubiquitous in daily living and are especially important in the healthcare setting. However, recent advances have revealed the pervasive nature of microplastics, which are formed by degradation of existing plastic products. Although the impact on human health has yet to be fully characterised, there is increasing evidence that microplastics can trigger inflammatory damage, microbial dysbiosis, and oxidative stress in humans. Although there are limited studies investigating their effect on the ocular surface, studies of microplastics on other organs provide some insights. The prevalence of plastic waste has also triggered public outcry, culminating in the development of legislation aimed at reducing microplastics in commercial products. We present a review outlining the possible sources of microplastics leading to ocular exposure, and analyse the possible mechanisms of ocular surface damage. Finally, we examine the utility and consequences of current legislation surrounding microplastic regulation.

Prevalence of diabetic retinopathy in women with pregestational diabetes during pregnancy and the postpartum.

BACKGROUND: Diabetic retinopathy (DR) may be affected by pregnancy. The majority of prevalence data regarding DR in pregnancy predate the advent of contemporary guidelines for diabetes management during pregnancy. This study reports DR prevalence and associated risk factors in women with pregestational diabetes during pregnancy and the postpartum in Australia. METHODS: A total of 172 pregnant women with type 1 (T1DM) or type 2 diabetes diagnosed pre-pregnancy were prospectively recruited from two obstetrics hospitals in Melbourne (November 2017-March 2020). Eye examinations were scheduled in each trimester, at 3-, 6-, and 12-months postpartum. DR severity was graded from two-field fundus photographs by an independent grader utilising the Airlie House Classification. Sight-threatening DR (STDR) was defined as the presence of diabetic macular oedema or proliferative DR. RESULTS: Overall, 146 (84.9%) women had at least one eye examination during pregnancy. The mean age was 33.8 years (range 19-51), median diabetes duration was 7.0 years (IQR 3.0-17.0), 71 women (48.6%) had T1DM. DR and STDR prevalence during pregnancy per 100 eyes was 24.3 (95% CI 19.7-29.6) and 9.0 (95% CI 6.1-12.9); while prevalence in the postpartum was 22.2 (95% CI 16.5-29.3) and 10.0 (95% CI 5.4-17.9), respectively. T1DM, longer diabetes duration, higher HbA1c in early pregnancy, and pre-existing nephropathy were significant risk factors. CONCLUSIONS: The prevalence of DR in pregnant women was similar to the non-pregnant diabetic population in Australia. One in nine participants had STDR during pregnancy and the postpartum, highlighting the need to optimise DR management guidelines in pregnancy given the significant risk of vision loss.

An overview of optometrists' diabetic retinopathy practice patterns - a cross-sectional survey.

PURPOSE: Contemporary eye care increasingly recommends the use of advanced retinal imaging technology. Anecdotal evidence suggests that this equipment is widely available in primary eye care settings; however, knowledge regarding how optometrists use this equipment in the context of diabetic retinopathy (DR) is limited. This study aimed to obtain a current overview of optometrists' clinical practice behaviours in the detection, screening, diagnosis and management of patients with diabetes. METHODS: A cross-sectional survey was designed to evaluate optometrists' self-reported clinical practice patterns and perceptions, as well as the availability and impact of retinal imaging equipment specific to DR and diabetic macular oedema (DMO) on optometrists' clinical practice. The survey invited participation from all optometrists practising in Australia. RESULTS: One hundred and sixty-seven optometrists participated. Optometrists' self-reported confidence in assessing DR and DMO was high. Optometrists' referral patterns considered the severity of DR and DMO before initiating referral to secondary ophthalmology care. Nearly all optometrists (98.8%) indicated that they had some form of retinal imaging equipment available to them in clinical practice. An optical coherence tomography (OCT) device was available to 75.5% of optometrists. A significant association between having an OCT device in the practice and higher self-reported confidence levels in the assessment of DMO was found. CONCLUSIONS: Many optometrists are well equipped with sophisticated retinal imaging technology for the provision of high-quality eye care. Enhancing optometric training and education programmes can maximise the community benefit of access to this equipment and improve delivery of eye care in the community.

Contrast Increment and Decrement Processing in Individuals With and Without Diabetes.

Purpose: Animal models suggest that ON retinal ganglion cells (RGCs) may be more vulnerable to diabetic insult than OFF cells. Using three psychophysical tasks to infer the function of ON and OFF RGCs, we hypothesized that functional responses to contrast increments will be preferentially affected in early diabetes mellitus (DM) compared to contrast decrement responses. Methods: Fifty-two people with DM (type 1 or type 2) (mean age = 34.8 years, range = 18-60 years) and 48 age-matched controls (mean age = 35.4 years, range = 18-60 years) participated. Experiment 1 measured contrast sensitivity to increments and decrements at four visual field locations. Experiments 2 and 3 measured visual temporal processing using (i) a response time (RT) task, and (ii) a temporal order judgment task. Mean RT and accuracy were collected for experiment 2, whereas experiment 3 measured temporal thresholds. Results: For experiment 1, the DM group showed reduced increment and decrement contrast sensitivity (F (1, 97) = 4.04, P = 0.047) especially for the central location. For experiment 2, those with DM demonstrated slower RT and lower response accuracies to increments and decrements (increments: U = 780, P = 0.01, decrements: U = 749, P = 0.005). For experiment 3, performance was similar between groups (F (1, 91) = 2.52, P = 0.137). Conclusions: When assessed cross-sectionally, nonselective functional consequences of retinal neuron damage are present in early DM, particularly for foveal testing. Whether increment-decrement functional indices relate to diabetic retinopathy (DR) progression or poorer visual prognosis in DM requires further study.

PARACENTRAL ACUTE MIDDLE MACULOPATHY IN A CASE OF HIGH-FLOW DIRECT CAROTID CAVERNOUS FISTULA.

PURPOSE: To report a case of paracentral acute middle maculopathy in a patient with high-flow carotid cavernous fistula. METHODS: A case report of a 53-year-old male patient who sustained an iatrogenic high-flow carotid cavernous fistula and secondary paracentral acute middle maculopathy. RESULTS: At review 1-week postembolization of the carotid cavernous fistula, there was no significant improvement in visual acuity, tests of optic nerve function, external ophthalmoplegia, and ptosis. Spectral domain optical coherence tomography was performed, which revealed hyperreflectivity of the parafoveal plexiform layers of the right eye with ill-defined margins straddling the inner nuclear layer. CONCLUSION: We suggest that spectral domain optical coherence tomography be performed in cases of high-flow direct carotid cavernous fistula where the best-corrected visual acuity is reduced out of keeping with other ophthalmic manifestations.

Global Estimates of Diabetic Retinopathy Prevalence and Progression in Pregnant Women With Preexisting Diabetes: A Systematic Review and Meta-analysis.

Importance: Diabetic retinopathy (DR) may be worsened by pregnancy in pregnant women with preexisting type 1 diabetes (T1D) or type 2 diabetes (T2D). Conflicting findings from previous studies have resulted in inconsistencies in guidelines regarding DR management in pregnancy. Global estimates of DR prevalence and progression in pregnancy are therefore required to provide clearer information about the overall true burden of DR in this population. Objective: To estimate the prevalence of DR and its progression rate in pregnant women with preexisting T1D or T2D diagnosed before pregnancy. Data Sources: For this systematic review and meta-analysis, conducted from November 27, 2018, to June 29, 2021, a systematic literature search was conducted in MEDLINE/Ovid, Embase/Ovid, and Scopus databases to identify English-language articles that were published from inception through October 2020. Study Selection: Observational studies that reported on DR and its changes in pregnant women with preexisting T1D and T2D. Data Extraction and Synthesis: Two independent reviewers extracted relevant data from each included study. Data were pooled using a random-effects model with the Freeman-Tukey double arcsine transformation. This study followed the Meta-analysis of Observational Studies in Epidemiology (MOOSE) reporting guidelines. Main Outcomes and Measures: Prevalence of any DR, proliferative DR (PDR), and DR progression rates. Results: A total of 18 observational studies involving 1464 pregnant women with T1D and 262 pregnant women with T2D were included in the analysis. The pooled prevalence of any DR and PDR in early pregnancy was 52.3 (95% CI, 41.9-62.6) and 6.1 (95% CI, 3.1-9.8) per 100 pregnancies, respectively. The pooled progression rate per 100 pregnancies for new DR development was 15.0 (95% CI, 9.9-20.8), worsened nonproliferative DR was 31.0 (95% CI, 23.2-39.2), progression from nonproliferative DR to PDR was 6.3 (95% CI, 3.3-10.0), and worsened PDR was 37.0 (95% CI, 21.2-54.0). DR progression rates per 100 pregnancies were similar between the T1D and T2D groups, except for the development of new DR (T1D groups: 15.8; 95% CI, 10.5-21.9; T2D groups: 9.0; 95% CI, 4.9-14.8). A global trend toward a lower DR progression rate was observed after the 1989 St Vincent Declaration. Conclusions and Relevance: Results of this systematic review and meta-analysis suggest that women with T1D and T2D had a similar risk of DR progression during pregnancy. Despite improvements in the management of diabetes and diabetes during pregnancy, DR prevalence and progression in pregnant women with diabetes remains higher than the nonpregnant population with diabetes, highlighting the need to improve DR management in pregnancy.

Identification of novel polyfluoroalkyl substances in surface water runoff from a chemical stockpile fire.

In 2018, over 30,000 L of fluorine-free firefighting foam was used to extinguish an industrial warehouse fire of uncharacterized chemical and industrial waste. Contaminated firewater and runoff were discharged to an adjacent freshwater creek in Melbourne, Australia. In this study, we applied nontarget analysis using liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) to 15 surface water samples to investigate the presence of legacy, novel and emerging per-and polyfluoroalkyl substances (PFAS). We identified six novel and emerging fluorotelomer-based fluorosurfactants in the Australian environment for the first time, including: fluorotelomer sulfonamido betaines (FTABs or FTSA-PrB), fluorotelomer thioether amido sulfonic acids (FTSASs), and fluorotelomer sulfonyl amido sulfonic acids (FTSAS-So). Legacy PFAS including C6-C8 perfluoroalkyl sulfonic acids, C4-C10 perfluoroalkyl carboxylic acids, and perfluoro-4-ethylcyclohexanesulfonate were also detected in surface water. Of note, we report the first environmental detection of ethyl 2-ethenyl-2-fluoro-1-(trifluoromethyl) cyclopropane-1-carboxylate. Analysis of several Class B certified fluorine-free foam formulations allowed for use in Australia revealed that there was no detectable PFAS. Patterns in the homologue profiles of fluorotelomers detected in surface water are consistent with environments impacted by fluorinated aqueous film-forming foams. These results provide strong evidence that firewater runoff of stockpiled fluorinated firefighting foam was the dominant source of detectable PFAS to the surrounding environment.

The cucumovirus 2b gene drives selection of inter-viral recombinants affecting the crossover site, the acceptor RNA and the rate of selection.

RNA-RNA recombination is an important pathway in virus evolution and has been described for many viruses. However, the factors driving recombination or promoting the selection of recombinants are still unclear. Here, we show that the small movement protein (2b) was able to promote selection of RNA 1/2-RNA 3 recombinants within a chimeric virus having RNAs 1 and 2 from cucumber mosaic virus, and RNA 3 from the related tomato aspermy virus, along with heterologous 2b genes. The source of the 2b also determined the selection of the acceptor RNA and the crossover site, as well as affecting the rate of selection of the recombinant RNAs. The nature of the RNA 3 also influenced the selection of the recombinant RNAs. A 163-nt tandem repeat in RNA 3 significantly affected the rate of selection of the recombinant RNA, while a single nucleotide within the repeat affected the crossover site. The recombination occurred in a non-random manner, involved no intermediates and probably was generated via a copy-choice mechanism during (+) strand RNA synthesis.

Blocking endothelial apoptosis revascularizes the retina in a model of ischemic retinopathy.

Aberrant, neovascular retinal blood vessel growth is a vision-threatening complication in ischemic retinal diseases. It is driven by retinal hypoxia frequently caused by capillary nonperfusion and endothelial cell (EC) loss. We investigated the role of EC apoptosis in this process using a mouse model of ischemic retinopathy, in which vessel closure and EC apoptosis cause capillary regression and retinal ischemia followed by neovascularization. Protecting ECs from apoptosis in this model did not prevent capillary closure or retinal ischemia. Nonetheless, it prevented the clearance of ECs from closed capillaries, delaying vessel regression and allowing ECs to persist in clusters throughout the ischemic zone. In response to hypoxia, these preserved ECs underwent a vessel sprouting response and rapidly reassembled into a functional vascular network. This alleviated retinal hypoxia, preventing subsequent pathogenic neovascularization. Vessel reassembly was not limited by VEGFA neutralization, suggesting it was not dependent on the excess VEGFA produced by the ischemic retina. Neutralization of ANG2 did not prevent vessel reassembly, but did impair subsequent angiogenic expansion of the reassembled vessels. Blockade of EC apoptosis may promote ischemic tissue revascularization by preserving ECs within ischemic tissue that retain the capacity to reassemble a functional network and rapidly restore blood supply.

Stability and competitiveness of interviral recombinant RNAs derived from a chimeric cucumovirus.

We previously described interviral recombinant RNAs derived from a chimeric virus having RNAs 1 and 2 of cucumber mosaic virus (CMV) with RNA 3 from the related tomato aspermy virus (TAV) and the 2b gene from either TAV or another strain of CMV. Here, we show that these interviral recombinant RNAs 3 were stable in the infected plants and could co-exist with their wild-type parental viral RNAs in the same plants, but their de novo generations were inhibited in the presence of the wild-type parental viral RNAs. The recombinant viral genomes did not prevent the replication of other viral RNAs or vice versa, but one of the interviral recombinant viruses induced different symptoms in Physalis floridana from those induced by the parental chimeric virus without the interviral RNA 3 recombinant. Factors such as the nature of the 2b gene and/or the presence or absence of competing wild-type parental RNAs influenced the generation of the recombinant RNAs described. Our data provide additional mechanistic insight into generation, stabilization and competition of recombinant viral RNA in infected host plants.

Replication of in vitro constructed viroid mutants: location of the pathogenicity-modulating domain of citrus exocortis viroid.

Sequence variants from field isolates of citrus exocortis viroid (CEV) that cause either mild or severe symptoms on tomato plants have previously been classified into two groups, A and B. These groups differ primarily in two domains, P(L) and P(R), of the proposed native structure. Infectivity studies with full-length cDNA clones of variants from each class have now directly confirmed the original correlation between Class A sequences and the severe phenotype and between Class B sequences and the mild phenotype. Direct evidence for this correlation could only be obtained by using individual sequence variants since field isolates of CEV have been shown to contain a mixture of RNA species. The construction and infectivity of chimaeric cDNA clones derived from mild and severe sequence variants of CEV has demonstrated that novel, infectious viroid molecules can be generated in vitro, and that P(L) is the pathogenicity-modulating domain. The role of the P(R) domain is not known but infectivity experiments with one chimaeric cDNA clone suggest that it may influence the efficiency of the infection or replication process of the viroid in the plant.

Polybrominated diphenyl ethers (PBDEs) in sediment by salinity and land-use type from Australia.

Brominated flame retardants, including polybrominated diphenyl ethers (PBDEs) have been incorporated in numerous products to reduce flammability. Depending on their bromination, PBDEs are relatively persistent in the environment and have the potential to bioaccumulate through the food web. The present study was initiated to provide a better understanding on the levels and possible origin of PBDEs in the aquatic environment of Australia. PBDEs were detected at 35 out of 46 sites and concentrations were relatively low in the majority of samples analysed. Mean+/-standard deviation and median SigmaPBDE concentrations across all sites were 4707+/-12,580 and 305 pg g(-1) dw, respectively, excluding the limit of detection. At 83% of sites, concentrations were below 1000 pg g(-1) dw, whereas elevated levels were found at sites downstream of STP outfalls and in areas dominated by industrial and urban land-use types. Concentrations of PBDEs differed significantly (p=0.007) among sites according to predominant type of land-use. Significantly (p=0.02) higher SigmaPBDE concentrations were also present in estuarine compared to freshwater environments, while PBDEs were below the limit of detection at the marine site. At most sites, BDE-209 contributed the highest proportion to the SigmaPBDE concentrations. The exception was one site with an elevated concentration of BDE-183. Sampling and analytical variability were investigated as part of this study. Results showed generally satisfactory results for repeat analysis at a different laboratory and low variability among samples collected within 1000 m at low contaminated sites. However, at sites with elevated PBDE levels, sampling variability was high, with several fold to magnitudes of higher concentrations present among replicate sites. Corresponding to findings from elsewhere, these results demonstrate that urban and industrial activities provide the key input sources of PBDEs to the aquatic environment and provide a baseline for further investigation into the specific origin of contamination, as well as information on the background status of aquatic sediment contamination with PBDEs.

Dioxin-like compounds in Australian sewage sludge--review and national survey.

An Australian survey of dioxin-like compounds in sewage sludge was conducted in two parts (a) a national survey, and (b) a time-study. All sewage sludge samples analysed as part of these studies had low overall concentrations of dioxin-like compounds. Out of 37 samples, all except one, were within the reported concentration range of soil within the Australian environment. The mean concentration of dioxin-like compounds in the Australian sewage sludge survey of 2006 was found to be 5.6 (s.d. 4.5) ng WHO(05) TEQkg(-1) (n=14) and were within the range of 1.2-15.3 ng WHO(05) TEQ kg(-1). All the Australian sewage sludge samples cited in these studies were below the Victorian EPA "investigation limit" of 50 ng WHO(98) TEQ kg(-1), and well below the European proposed guidelines of 100 ng I-TEQ kg(-1). The burden of dioxin-like compounds in Australian sewage sludge is low and its land application as biosolids is not likely to pose a problem. A general positive relationship was found between population of the town producing the waste and both dioxin-like PCDD/Fs and dioxin-like PCBs. The one exception to this trend was sludge from a town that had a history of smelting and had a relatively high burden of dioxin-like compounds. Sludge from one rural WWTP also had a higher burden of dioxin-like compounds. The treatment plant services a geographically isolated town with a low population and no known emitters of dioxin-like compounds. However, this sample also had a relatively high burden of dioxin-like PCBs, which could be the source of the dioxin-like PCDD/Fs found in this sludge. The time study analyzing sludges from three WWTP from the same city between the years 2002 and 2006 found no apparent difference between WWTPs, but a statistically significant decline of 1.49 ng WHO(05) TEQ kg(-1) per year. Also, a comprehensive review of the scientific literature, presents typical levels and sources of dioxin-like compounds in international sewage sludges.

Persistent organochlorine pesticides in human milk samples from Australia.

Human milk has been used as a surrogate for the assessment of body burden and exposure to persistent lipophilic organochlorine pesticides (OCPs). With the exception of restricted use of mirex, the use of persistent, lipophilic OCPs has been banned in Australia since the 1980s. The decline of human body burden of OCPs following their ban in many industrialised countries is well recorded worldwide from the 1970s until the 1990s though little is known on whether these trends are continuing. In this study, 157 human milk samples collected during 2002 and 2003 as well as 24 samples collected in 1993 were analysed as 20 regional pools for 17 OCPs. OCPs were detected in all pooled human milk samples from 2002/03 typically with highest concentrations of p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) (mean+/-standard deviation; median concentration 311+/-174; 279 ng g(-1) lipid) followed by beta-hexachlorocyclohexane (beta-HCH) (80+/-173; 21 ng g(-1) lipid). Other OCPs consistently detected included dieldrin (16+/-6; 17 ng g(-1) lipid), hexachlorobenzene (HCB) (18+/-16; 14 ng g(-1) lipid), transnonachlor (11+/-5; 9 ng g(-1) lipid) and p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) (9+/-6; 7 ng g(-1) lipid). The results from this study indicated that following a substantial decline of OCP concentrations from the early 1980s to the 1990s, little decline could be observed since then. Furthermore the use of multivariate statistics indicated some regional trends with slightly higher levels of the broadly used insecticides DDT and HCH in both historic and recent samples from Melbourne, whereas, sample pools collected from mothers that lived in rural Queensland and New South Wales as well as Adelaide and Sydney showed comparatively higher levels of heptachlor and dieldrin - both of which have been used for termite treatment. These results indicate that even 20 years after the discontinuation of usage, historical use of OCPs rather than exposure via global transport of OCPs is responsible for continuous low exposure in Australia.

Polybrominated diphenyl ethers and polybrominated biphenyls in Australian sewage sludge.

This paper presents a brief review of the international scientific literature of polybrominated diphenyl ethers (PBDEs) and polybrominated biphenyls (PBBs) in sewage sludge and a survey of these compounds in sewage sludge from 16 Australian wastewater treatment plants (WWTPs). The SigmaPBDE mean concentration in the Australian study was 1137microgkg(-1) dry weight (d.w.) (s.d. 1116) and ranged between 5 and 4 230microgkg(-1)d.w. The urban mean of 1308microgkg(-1) (s.d. 1320) and the rural mean of 911microgkg(-1) (s.d. 831) are not statistically different and are similar to levels in European sludges. Principal components analysis was performed on the data set and revealed that 76% of the data variation could be explained by two components that corresponded to overall concentration of the pentaBDE and the decaBDE commercial formulations. An analysis of variance was performed comparing PBDEs levels at three WWTPs over the years 2005 and 2006, finding differences between treatment plants (BDE-47) but no significant difference in PBDE levels in the years 2005 and 2006. Low levels of BB-153 were detected in all samples of this survey (n=16); mean 0.6microgkg(-1)d.w. (s.d. 0.5). This compound has rarely been reported in any other study of sewage sludges undertaken outside Australia. This work highlights the need for a risk assessment of PBDEs in sewage sludge when used for land application, taking into account typical levels found in Australian sludges and soils.

Dioxin- and POP-contaminated sites--contemporary and future relevance and challenges: overview on background, aims and scope of the series.

BACKGROUND, AIM AND SCOPE: Once they have been generated, polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and other persistent organic pollutants (POPs) can persist in soils and sediments and in waste repositories for periods extending from decades to centuries. In 1994, the US EPA concluded that contaminated sites and other reservoirs are likely to become the major source of contemporary pollution problems with these substances. With this in mind, this article is the first in a new series in ESPR under the title 'Case Studies on Dioxin and POP Contaminated Sites--Contemporary and Future Relevance and Challenges', which will address this important issue. The series will document various experiences from sites contaminated with PCDD/F and other POPs. This article provides an overview of the content of the articles comprising the series. In addition, it provides a review of the subject in its own right and identifies the key issues arising from dioxin/POP-contaminated sites. Additionally, it highlights the important conclusions that can be drawn from these examples. The key aim of this article and of the series as a whole is to provide a comprehensive overview of the types of PCDD/F contaminated sites that exist as a result of historical activities. It details the various processes whereby these sites became contaminated and attempts to evaluate their contemporary relevance as sources of PCDD/Fs and other POPs. It also details the various strategies used to assess these historical legacies of contamination and the concepts developed, or which are under development, to effect their remediation. MAIN FEATURES: Special sessions on 'Contaminated sites--Cases, remediation, risk and policy' were held at the DIOXIN conferences in 2006 and 2007, and this theme will be continued at DIOXIN 2008 to be held in Birmingham. Selected cases from the approximately 70 contributions made to these sessions, together with some additional invited case studies are outlined together with the key issues they raise. By evaluating these cases and adding details of experiences published in the current literature, an overview will be given of the different features and challenges of dioxin and POP-contaminated sites. RESULTS: This article provides a systematic categorisation of types of PCDD/F and POP-contaminated sites. These are categorised according to the chemical or manufacturing process, which generated the PCDD/Fs or POPs and also includes the use and disposal aspects of the product life cycle in question. The highest historical PCDD/F and dioxin-like polychlorinated biphenyl (PCB) contamination burdens have arisen as a result of the production of chlorine and of chlorinated organic chemicals. In particular, the production of chlorinated pesticides, PCBs and the related contaminated waste streams are identified being responsible for historical releases of toxic equivalents (TEQs) at a scale of many tonnes. Along with such releases, major PCDD/F contaminated sites have been created through the application or improper disposal of contaminated pesticides, PCBs and other organochlorine chemicals, as well through the recycling of wastes and their attempted destruction. In some extreme examples, PCDD/F contaminated sites have also resulted from thermal processes such as waste incinerators, secondary metal industries or from the recycling or deposition of specific waste (e.g. electronic waste or car shredder wastes), which often contain chlorinated or brominated organic chemicals. The examples of PCDD/F and dioxin-like PCB contamination of fish in European rivers or the impact of contaminated sites upon fishing grounds and upon other food resources demonstrate the relevance of these historical problems to current and future human generations. Many of the recent food contamination problems that have emerged in Europe and elsewhere demonstrate how PCDD/F and dioxin like PCBs from historical sources can directly contaminate human and animal feedstuffs and indeed highlight their considerable contemporary relevance in this respect. Accordingly, some key experiences and lessons learnt regarding the production, use, disposal and remediation of POPs from the contaminated sites are summarised. DISCUSSION: An important criterion for evaluating the significance and risks of PCDD/Fs and other POPs at contaminated sites is their present or future potential for mobility. This, in turn, determines to a large degree their propensity for off-site transport and environmental accessibility. The detailed evaluation of contaminated site cases reveals different site-specific factors, which influence the varied pathways through which poor water-soluble POPs can be mobilised. Co-contaminants with greater water solubility are also typically present at such sites. Hence, pumping of groundwater (pump and treat) is often required in addition to attempting to physically secure a site. At an increasing number of contaminated sites, securing measures are failing after relatively short time spans compared to the time horizon, which applies to persistent organic pollutant contamination. Due to the immense costs and challenges associated with remediation of contaminated sites 'monitored natural attenuation' is increasingly gaining purchase as a conceptual remediation approach. However, these concepts may well prove limited in their practical application to contaminated sites containing persistent organic pollutants and other key pollutants like heavy metals. CONCLUSIONS: It is inevitable, therefore, that dioxin/POP-contaminated sites will remain of contemporary and future relevance. They will continue to represent an environmental issue for future generations to address. The securing and/or remediation of dioxin/POP-contaminated sites is very costly, generally in the order of tens or hundreds of millions of dollars. Secured landfills and secured production sites need to be considered as constructions not made for 'eternity' but built for a finite time scale. Accordingly, they will need to be controlled, supervised and potentially repaired/renewed. Furthermore, the leachates and groundwater impacted by these sites will require ongoing monitoring and potential further remediation. These activities result in high maintenance costs, which are accrued for decades or centuries and should, therefore, be compared to the fully sustainable option of complete remediation. The contaminated site case studies highlight that, while extensive policies and established funds for remediation exist in most of the industrialised western countries, even these relatively well-regulated and wealthy countries face significant challenges in the implementation of a remediation strategy. This highlights the fact that ultimately only the prevention of contaminated sites represents a sustainable solution for the future and that the Polluter Pays Principle needs to be applied in a comprehensive way to current problems and those which may emerge in the future. RECOMMENDATIONS AND PERSPECTIVES: With the continuing shift of industrial activities in developing and transition economies, which often have poor regulation (and weak self-regulation of industries), additional global challenges regarding POPs and other contaminated sites may be expected. In this respect, a comprehensive application of the "polluter pays principle" in these countries will also be a key to facilitate the clean-up of contaminated areas and the prevention of future contaminated sites. The threats and challenges of contaminated sites and the high costs of securing/remediating the problems highlight the need for a comprehensive approach based upon integrated pollution prevention and control. If applied to all polluting (and potentially polluting) industrial sectors around the globe, such an approach will prove to be both the cheapest and most sustainable way to underpin the development of industries in developing and transition economies.