Urine antimony and risk of cardiovascular disease - A prospective case-cohort study in Danish Non-Smokers

BACKGROUND

Limited evidence suggests that antimony induces vascular inflammation and oxidative stress and may play a role in cardiovascular disease (CVD) risk. However, few studies have examined whether environmental antimony from sources other than tobacco smoking is related with CVD risk. The general population may be exposed through air, drinking water, and food that contains antimony from natural and anthropogenic sources, such as mining, coal combustion, and manufacturing.

OBJECTIVES

To examine the association of urine antimony with incident acute myocardial infarction (AMI), heart failure, and stroke among people who never smoked tobacco.

METHODS

Between 1993 and 1997, the Danish Diet, Cancer and Health (DCH) cohort enrolled participants (ages 50-64 years), including n = 19,394 participants who reported never smoking at baseline. Among these never smokers, we identified incident cases of AMI (N = 809), heart failure (N = 958), and stroke (N = 534) using the Danish National Patient Registry. We also randomly selected a subcohort of 600 men and 600 women. We quantified urine antimony concentrations in samples provided at enrollment. We used modified Cox proportional hazards models to estimate adjusted hazard ratios (HR) for each incident CVD outcome in relation to urine antimony, statistically adjusted for creatinine. We used a separate prospective cohort, the San Luis Valley Diabetes Study (SLVDS), to replicate these results.

RESULTS

In the DCH cohort, urine antimony concentrations were positively associated with rates of AMI and heart failure (HR = 1.52; 95%CI = 1.12, 2.08 and HR = 1.58; 95% CI = 1.15, 2.18, respectively, comparing participants in the highest (>0.09 µg/L) with the lowest quartile (<0.02 µg/L) of antimony). In the SLVDS cohort, urinary antimony was positively associated with AMI, but not heart failure.

DISCUSSION

Among this sample of Danish people who never smoked, we found that low levels of urine antimony are associated with incident CVD. These results were partially confirmed in a smaller US cohort.

Systemic exposure and urinary excretion of vanadium following perinatal subchronic exposure to vanadyl sulfate and sodium metavanadate via drinking water

Vanadium is a ubiquitous environmental contaminant although there are limited data to assess potential adverse human health impact following oral exposure. In support of studies investigating the subchronic toxicity of vanadyl sulfate (V4+) and sodium metavanadate (V5+) following perinatal exposure via drinking water in male and female rats, we have determined the internal exposure and urinary excretion of total vanadium at the end of study. Water consumption decreased with increasing exposure concentration following exposure to both compounds. Plasma and urine vanadium concentration normalized to total vanadium consumed per day increased with the exposure concentration of vanadyl sulfate and sodium metavanadate suggesting absorption increased as the exposure concentration increased. Additionally, females had higher concentrations than males (in plasma only for vanadyl sulfate exposure). Animals exposed to sodium metavanadate had up to 3-fold higher vanadium concentration in plasma and urine compared to vanadyl sulfate exposed animals, when normalized to total vanadium consumed per day, demonstrating differential absorption, distribution, metabolism, and excretion properties between V5+ and V4+ compounds. These data will aid in the interpretation of animal toxicity data of V4+ and V5+ compounds and determine the relevance of animal toxicity findings to human exposures.

Urinary Cadmium and Incident Heart Failure: A Case-Cohort Analysis Among Never-Smokers in Denmark

BACKGROUND

Epidemiologic studies suggest cadmium exposure is associated with cardiovascular disease risk, including heart failure. However, prior findings may be influenced by tobacco smoking, a dominant source of cadmium exposure and risk factor for heart failure. The present study leverages up to 20 years of follow-up in the Danish Diet, Cancer and Health cohort to examine the relationship between urinary cadmium and incident heart failure among people who never smoked.

METHODS

Between 1993 and 1997, 19,394 never-smoking participants (ages 50-64 years) enrolled and provided a urine sample. From this sample, we randomly selected a subcohort of 600 men and 600 women and identified 958 incident heart failure cases occurring between baseline and 2015. Using a case-cohort approach, we estimated adjusted hazard ratios (aHR) for heart failure in Cox proportional hazards models with age as the time scale.

RESULTS

Participants had relatively low concentrations of urinary cadmium, as expected for never smokers (median = 0.20; 25th, 75th = 0.13, 0.32 μg cadmium/g creatinine). In adjusted models, we found that higher urinary cadmium was associated with a higher rate of incident heart failure overall (aHR = 1.1 per interquartile range difference [95% CI = 1.0, 1.2). In sex-stratified analyses, the association seemed restricted to men (aHR = 1.5 [95% CI = 1.2, 1.9]).

CONCLUSIONS

In this cohort of people who never smoked tobacco, environmental cadmium was positively associated with incident heart failure, especially among men.

Validation of Analytical Method for Determination of Thallium in Rodent Plasma and Tissues by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)

Thallium (Tl) can be released as a byproduct of smelting, mining, and other industries, causing human exposure. There are knowledge gaps on the toxicity of thallium compounds, so the National Toxicology Program is investigating the toxicity of thallium (I) sulfate in rodents. We developed and validated a method to quantitate Tl in rodent plasma and secondary matrices. Primary matrix standards and validation samples were digested with nitric acid and analyzed for Tl by inductively-coupled plasma - mass spectrometry (ICP-MS). Method performance was validated for linearity, accuracy, precision, and other criteria. Calibration was linear from 1.25 to 500 ng Tl/mL plasma; accuracy (RE) was -5.9 to 2.6% for all calibration standards. The lower limit of quantitation (LLOQ) was 1.25 ng Tl/mL plasma, and the limit of detection was 0.0370 ng Tl/mL plasma. Intra- and interday RE and precision (RSD) were -5.6 to -1.7% and ≤0.8% (intraday) and -4.8 to -1.3% and ≤4.3% (interday), respectively, at three sample concentration levels. Standards up to 10.0 × 10³ ng/mL could be analyzed by dilution with digested blank matrix, with -6.4% RE and 5.4% RSD. Method was also evaluated in post-natal day 4 (PND4) Hsd:Sprague Dawley SD (HSD) dam and pup plasma, gestation day 18 (GD 18) HSD rat fetal homogenate, HSD rat urine, female HSD rat brain homogenate, female B6C3F1 mouse plasma. Background Tl was detected in control fetal and brain homogenates and urine at < 30% of LLOQ response. Results demonstrate that the method is suitable for determination of Tl in rodent matrices for toxicology studies.

Quantitation of Total Vanadium in Rodent Plasma and Urine by Inductively Coupled Plasma - Mass Spectrometry (ICP-MS)

Human exposure to vanadium (V) is anticipated because it is a drinking water contaminant. Due to limited data on soluble V salts, the National Toxicology Program is investigating the toxicity in rodents following drinking water exposure. Measurement of internal V dose allows for interpretation of toxicology data. The objective of this study was to develop and validate an inductively coupled plasma-mass spectrometric method to quantitate total V in rat plasma. The method was linear (r ≥ 0.99) from 5.00 - 1,000 ng V/mL. Intra- and inter-day relative error (% RE) and relative standard deviation (% RSD) of spiked plasma samples were 8.5% - 15.6% RE and ≤ 1.8% RSD and 7.3% - 11.7% RE and ≤ 3.1% RSD, respectively. The limit of detection was 0.268 ng V/mL plasma and absolute percent recovery was 113%. Standards up to 7,500 ng V/mL plasma were diluted into the validated range (5.6% RE, 0.9% RSD). V in extracted plasma samples over 15 days at ambient and refrigerated conditions was from 97.7 - 126% of day 0. Determined plasma V concentrations after three freeze-thaw cycles and after frozen storage for up to 63 days ranged from 100 - 106% and 100 - 122% of day 0, respectively. The method was extended to rat urine (accuracy and precision -2.0 - 0.3% RE and <0.6% RSD, respectively for same linear range). These data demonstrate that the method is suitable to quantitate V in rat plasma and urine.

Salicylate coordination in metal-protochelin complexes

Molybdenum (Mo) is an essential trace element for bacteria that is utilized in myriad metalloenzymes that directly couple to the biogeochemical cycling of nitrogen, sulfur, and carbon. In particular, Mo is found in the most common nitrogenase enzyme, and the scarcity and low bioavailability of Mo in soil may be a critical factor that contributes to the limitation of nitrogen fixation in forests and agroenvironments. To overcome this scarcity, microbes produce exudates that specifically chelate scarce metals, promoting their solubilization and uptake. Here, we have determined the structure and stability constants of Mo bound by protochelin, a siderophore produced by bacteria under Mo-depleted conditions. Spectrophotometric titration spectra indicated a coordination shift from a catecholate to salicylate binding mode for Mo^VI-protochelin (Mo-Proto) complexes at pH < 5. pKa values obtained from analysis of titrations were 4.8 ± 0.3 for Mo^VIO₂H₃Proto^- and 3.3 ± 0.1 for Mo^VIO₂H₄Proto. The occurrence of negatively charged Mo-Proto complexes at pH 6 was also confirmed by mass spectrometry. K-edge Extended X-ray absorption fine structure spectroscopy confirmed the change in Mo coordination at low pH, and structural fitting provides insights into the physical architecture of complexes at neutral and acidic pH. These findings suggest that Mo can be chelated by protochelin across a wide environmental pH range, with a coordination shift occurring at pH < 5. This chelation and associated coordination shift may impact biological availability and mineral surface retention of Mo under acidic conditions.

Relationship between Urine Creatinine and Urine Osmolality in Spot Samples among Men and Women in the Danish Diet Cancer and Health Cohort

Assays of urine biomarkers often use urine creatinine to account for urinary dilution, even though creatinine levels are influenced by underlying physiology and muscle catabolism. Urine osmolality-a measure of dissolved particles including ions, glucose, and urea-is thought to provide a more robust marker of urinary dilution but is seldom measured. The relationship between urine osmolality and creatinine is not well understood. We calculated correlation coefficients between urine creatinine and osmolality among 1375 members of a subcohort of the Danish Diet, Cancer, and Health Cohort, and within different subgroups. We used linear regression to relate creatinine with osmolality, and a lasso selection procedure to identify other variables that explain remaining variability in osmolality. Spearman correlation between urine creatinine and osmolality was strong overall (ρ = 0.90; 95% CI: 0.89-0.91) and in most subgroups. Linear regression showed that urine creatinine explained 60% of the variability in urine osmolality, with another 9% explained by urine thallium (Tl), cesium (Cs), and strontium (Sr). Urinary creatinine and osmolality are strongly correlated, although urine Tl, Cs, and Sr might help supplement urine creatinine for purposes of urine dilution adjustment when osmolality is not available.

Aligning Diet, Health and Planet in the Older Population

Background

The global food system faces incessant and complex challenges of providing food for a growing population while remaining within planetary boundaries. Agriculture and food production depletes finite resources such as land, water and fossil fuels, and contributes to climate change. GHG emissions occur at every stage in the life cycle of a food from primary production through to processing, packaging, distribution, consumption, and waste. This results in approximately 34% of anthropogenic GHGEs globally. Thus, the aim of this study is to determine the levels of and contributors to dietary carbon footprint among older Irish adults.

Methods

Diet quality metrics explore associations between dietary patterns and health outcomes. A Food Frequency Questionnaire was used to assess dietary intake of participants in the Mitchelstown Cohort Study. To determine carbon footprint, foods were linked to CO2eq emission factors from life cycle assessment studies. The DASH and Mediterranean diet scores were used to determine if higher adherence to these recommended diets was associated with improved health outcomes and lower dietary GHGEs.

Results

Preliminary results suggest that the daily CO2eq is similar to a previous Irish study, which found that the daily dietary intake was 6.5 kg of CO2eq per person. As expected, consumption of red meat was the highest contributor to dietary carbon footprint. Fruit and vegetable consumption was low despite these foods having a lower carbon footprint.

Conclusions

The environmental impacts of current dietary patterns are substantial, threatening ecological integrity. Greater adherence to well-characterized diets has been associated with lower diet-related GHGE. Transforming our diets is required to build a resilient and sustainable food system, while safeguarding planetary health. However, nutrition and long-term health must remain a key component of any dietary change particularly in vulnerable and nutritionally compromised populations.

Key messages

Food systems and diets thereof are inextricably linked with nutrition, health and environmental issues. Dietary transitions are needed to reduce global burden of disease and environmental degradation. Consideration on the feasibility of adopting sustainable diets among older populations to ensure healthy ageing is required. Trade-offs arise between protein requirements and environmental impacts.

Urine cadmium and acute myocardial infarction among never smokers in the Danish Diet, Cancer and Health cohort

Cadmium exposure has been associated with cardiovascular disease. Cigarette smoking is a key source of cadmium exposure and thus a potential confounder in observational studies of environmental cadmium and cardiovascular disease that include tobacco smokers. We leveraged up to 20 years of follow-up in the Danish Diet, Cancer and Health cohort to test the hypothesis that cadmium exposure is associated with acute myocardial infarction (AMI) among people who never smoked. Between 1993 and 1997, 19,394 never-smoking participants (ages 50-64 years) were enrolled and provided a urine sample. From this sample, we randomly selected a subcohort of 600 males and 600 females. We identified 809 AMI cases occurring between baseline and the end of 2015 using the Danish National Patient Registry. We quantified cadmium, creatinine, and osmolality in baseline urine samples. Using an unweighted case-cohort approach, we estimated adjusted hazard ratios (aHR) for AMI in Cox proportional hazards models with age as the time axis. Participants had relatively low concentrations of urinary cadmium, as expected for never smokers (median = 0.20; 25th, 75th = 0.13, 0.32 μg cadmium/g creatinine). We did not find strong evidence to support an association between higher urinary cadmium and AMI when comparing the highest versus lowest quartile (aHR = 1.16; 95% CI: 0.86 - 1.56) and per IQR increment in cadmium concentration (aHR = 1.02; 95% CI: 0.93 - 1.12). Results were not materially different across strata defined by sex. Results were generally similar using creatinine or osmolality to account for differences in urine dilution. While cadmium exposure has been identified as a risk factor for cardiovascular disease, we did not find strong evidence that urinary cadmium at relatively low-levels is associated with AMI among people who have never smoked.

Internal dose of vanadium in rats following repeated exposure to vanadyl sulfate and sodium orthovanadate via drinking water

Vanadium is a ubiquitous environmental contaminant that exists in multiple oxidation states. Humans are exposed to vanadyl (V4+) and vanadate (V5+) from dietary supplements, food, and drinking water and hence there is a concern for adverse human health. The current investigation is aimed at identifying vanadium oxidation states in vitro and in vivo and internal concentrations following exposure of rats to vanadyl sulfate (V4+) or sodium metavanadate (V5+) via drinking water for 14 d. Investigations in simulated gastric and intestinal fluids showed that V4+ was stable in gastric fluid while V5+ was stable in intestinal fluid. Analysis of rodent plasma showed that the only vanadium present was V4+, regardless of the exposed compound suggesting conversion of V5+ to V4+ in vivo and/or instability of V5+ species in biological matrices. Plasma, blood, and liver concentrations of total vanadium, after normalizing for vanadium dose consumed, were higher in male and female rats following exposure to V5+ than to V4+. Following exposure to either V4+ or V5+, the total vanadium concentration in plasma was 2- to 3-fold higher than in blood suggesting plasma as a better matrix than blood for measuring vanadium in future work. Liver to blood ratios were 4-7 demonstrating significant tissue retention following exposure to both compounds. In conclusion, these data point to potential differences in absorption and disposition properties of V4+ and V5+ salts and may explain the higher sensitivity in rats following drinking water exposure to V5+ than V4+ and highlights the importance of internal dose determination in toxicology studies.

The Influence of Different Physical Activity Behaviours on the Gut Microbiota of Older Irish Adults

OBJECTIVE

A 24-hour day is made up of time spent in a range of physical activity (PA) behaviours, including sleep, sedentary time, standing, light-intensity PA (LIPA) and moderate-to-vigorous PA (MVPA), all of which may have the potential to alter an individual's health through various different pathways and mechanisms. This study aimed to explore the relationship between PA behaviours and the gut microbiome in older adults.

DESIGN

Cross-sectional study.

SETTINGS AND PARTICIPANTS

Participants (n=100; age 69.0 [3.0] years; 44% female) from the Mitchelstown Cohort Rescreen (MCR) Study (2015-2017).

METHODS

Participants provided measures of gut microbiome composition (profiled by sequencing 16S rRNA gene amplicons), and objective measures of PA behaviours (by a 7-day wear protocol using an activPAL3 Micro).

RESULTS

Standing time was positively correlated with the abundance of butyrate-producing and anti-inflammatory bacteria, including Ruminococcaceae, Lachnospiraceae and Bifidobacterium, MVPA was positively associated with the abundance of Lachnospiraceae bacteria, while sedentary time was associated with lower abundance of Ruminococcaceae and higher abundance of Streptococcus spp.

CONCLUSION

Physical activity behaviours appear to influence gut microbiota composition in older adults, with different PA behaviours having diverging effects on gut microbiota composition.

Has the European Union created a healthy food environment for its citizens? Application of the Food Environment Policy Index (Food-EPI)

Background

European Union (EU) Member states' food environments are shaped by both national and EU policies. To date however, studies assessing food environment policies developed and set by the EU are scarce. The aim of this study was to assess the strength of EU policies to improve food environments as well as to assess the extent these policies could lead to a decrease or widening of socio-economic inequalities in dietary intake.

Methods

We compiled evidence on the EU policies for each of the Food-EPI 47 indicators. A European panel of independent, non-government experts (N = 30) specialized in nutrition, obesity or chronic diseases, using the Food-EPI evidence, rated the strength of EU policies to improve food environments during an online survey in February-March 2020. The experts also rated to which extent policies could lead to a decrease or widening of socio-economic inequalities in dietary intake. In addition, experts formulated actions to improve EU food environment policies, which were prioritized during a follow-up online survey.

Results

The overview of EU-level policies resulted in a 79-pages document, describing policies (or the lack thereof) for each of the 47 Food-EPI indicators. This document has been verified for completeness and accuracy by EU governmental officials. The evidence document shows that the EU has mainly binding legislation on the food labelling whereas policies on the other Food-EPI domains are mostly voluntary. Results from the online survey and the formulated prioritized actions will be presented during the conference. The results will reflect the experts' ratings supported by documented evidence and will provide meaningful guidance to EU officials and public health advocates in their efforts to improve the food environment policies set by the EU.

Total sulfur analysis of fine particulate mass on nylon filters by ICP-OES

Sulfur (S) and sulfate (SO₄ ^2- ) in fine particulate matter (PM_2.5 ) are monitored by the Interagency Monitoring of Protected Visual Environments (IMPROVE) network at remote and rural sites across the United States. Within the IMPROVE network, S is determined from X-ray fluorescence (XRF) spectroscopy from a Teflon filter, and SO₄ ^2- is determined via ion chromatography (IC) from a nylon filter. Differences in S and SO₄ ^2- estimates may indicate the presence of organosulfur (OS) species or biases between sampling and analytical methods. To reduce potential biases, an inductively coupled plasma-optical emission spectroscopy (ICP-OES) method was developed to allow for analysis of SO₄ ^2- and S from a single filter extract. Sulfur (ICP-OES) and SO₄ ^2- (IC) estimates from 2016 IMPROVE filters correlated strongly, suggesting that, on average, ICP-OES accurately estimated S. However, observed differences between slopes suggested the presence of water-soluble OS species, especially during summer. Organosulfur species are important indicators of secondary organic aerosols formed through reactions of biogenic and anthropogenic pollutants and can be quantified through laboratory techniques such as reverse-phase liquid chromatography (RPLC) or hydrophilic liquid interaction chromatography (HILIC) coupled to electrospray ionization-high-resolution tandem mass spectrometry (RPLC/ESI-HR-MS/MS and HILIC/ESI-HR-MS/MS, respectively), and field techniques using Aerodyne aerosol mass spectrometry (AMS). However, these methods are costly and introduce relatively large uncertainties when scaled for large networks such as IMPROVE. The method described in this report provides an inexpensive complement to XRF, which measures total S (insoluble and water-soluble S) to estimate water-soluble S and OS concentrations in PM.

Barriers and facilitators to adoption, implementation and sustainment of obesity prevention interventions in schoolchildren- a DEDIPAC case study

BACKGROUND

The aim of the study was to explore the implementation of school based diet and physical activity interventions with respect to the barriers and facilitators to adoption, implementation and sustainability; supportive actions required for implementation and recommendations to overcome identified barriers. Two interventions rolled out nationally in Ireland were chosen; Food Dudes, a programme to encourage primary school children to consume more fruit and vegetables and Green Schools Travel (GST), an active travel to school programme in primary and secondary schools. Trained school coordinators (teachers) cascade the programmes to other teaching staff.

METHODS

Multiple case study design using qualitative semi-structured interviews with key stakeholders: primary and secondary school teachers, school coordinators, project coordinators/managers, funders and intermediaries. Fifteen interviews were conducted. Data were coded using a common categorization matrix. Thematic analysis was undertaken using the Adoption, Implementation and Maintenance elements of the RE-AIM implementation framework.

RESULTS

Good working relationships within and across government departments, intermediaries and schools were critical for intervention adoption, successful implementation and sustainability. Organisational and leadership ability of coordinators were essential. Provision of participation incentives acted as motivators to engage children's interest. A deep understanding of the lives of the target children was an important contextual factor. The importance of adaptation without compromising core components in enhancing intervention sustainability emerged. Successful implementation was hindered by: funding insecurity, school timetable constraints, broad rather than specific intervention core components, and lack of agreement on conduct of programme evaluation. Supportive actions for maintenance included ongoing political support, secure funding and pre-existing healthy lifestyle policies.

CONCLUSIONS

Successful implementation and scale up of public health anti-obesity interventions in schools is dependent on good contextual fit, engagement and leadership at multiple levels and secure funding. Recommendations to overcome barriers include: capacity to deliver within an already overcrowded curriculum and clear specification of intervention components within a conceptual framework to facilitate evaluation. Our findings are generalisable across different contexts and are highly relevant to those involved in the development or adaptation, organisation or execution of national public health interventions: policy makers, guidelines developers, and staff involved in local organisation and delivery.

Plating up appropriate portion sizes for children: a systematic review of parental food and beverage portioning practices

Consumption of larger portion sizes is associated with higher energy intake and weight status in children. As parents play a pivotal role in child feeding, we synthesized literature on 'parental portioning practices' using a mixed methods systematic design to inform future strategies addressing portion sizes served to children. Electronic databases PubMed, EMBASE, SCOPUS, PsycINFO and CINAHL Plus were searched. Two reviewers independently screened 385 abstracts and assessed 71 full-text articles against eligibility criteria: studies assessing portioning of foods or beverages by parent(s) with ≥1 child aged 2-12 years. Narrative synthesis of 14 quantitative studies found that portion sizes parents serve vary substantially and are influenced by amounts parents serve themselves, perceived child hunger and parent and child body size. Thematic synthesis of 14 qualitative studies found that parents serve the portion sizes they learn to be appropriate for their child to be fed. Portioning is influenced by parents' desires for a healthy child with a balanced diet. Future guidance on appropriate portion sizes for children would ideally present recommended portion sizes for first serving, incremental with age. Future research is however needed to assess the adoption and efficacy of providing such guidance to families.

Low levels of lead and glutathione markers of redox status in human blood

Exposure to lead (Pb) is implicated in a plethora of health threats in both adults and children. Increased exposure levels are associated with oxidative stress in the blood of workers exposed at occupational levels. However, it is not known whether lower Pb exposure levels are related to a shift toward a more oxidized state. To assess the association between blood lead level (BLL) and glutathione (GSH) redox biomarkers in a population of healthy adults, BLL and four GSH markers (GSH, GSSG, GSH/GSSG ratio and redox potential E h ) were measured in the blood of a cross-sectional cohort of 282 avid seafood-eating healthy adults living on Long Island (NY). Additionally, blood levels of two other metals known to affect GSH redox status, selenium (Se) and mercury (Hg), and omega-3 index were tested for effect modification. Regression models were further adjusted for demographic and smoking status. Increasing exposure to Pb, measured in blood, was not associated with GSSG, but was associated with lower levels of GSH/GSSG ratio and more positive GSH redox potential E h , driven by its association with GSH. No effect modification was observed in analyses stratified by Hg, Se, omega-3 index, sex, age, or smoking. Blood Pb is associated with lower levels of GSH and the GSH/GSSG ratio in this cross-sectional study of healthy adults.

The kinetics of dimethylhydroxypyridinone interactions with iron(iii) and the catalysis of iron(iii) ligand exchange reactions: implications for bacterial iron transport and combination chelation therapies

Many microbes acquire environmental Fe by secreting organic chelators, siderophores, which possess the characteristics of a high and specific binding affinity for iron(iii) that results in the formation of thermodynamically stable, and kinetically inert iron(iii) complexes. Mechanisms to overcome the kinetic inertness include the labilization of iron(iii) by means of ternary complex formation with small chelators. This study describes a kinetic investigation of the labilization of iron(iii) between two stable binding sites, the prototypical siderophore ferrioxamine B and EDTA, by the bidentate siderophore mimic, 1,2-dimethyl-3-hydroxy-4-pyridinone (L1, H(DMHP)). The proposed mechanism is substantiated by investigating the iron(iii) exchange reaction between ferrioxamine B and H(DMHP) to form Fe(DMHP)3, as well as the iron(iii) exchange from Fe(DMHP)3 to EDTA. It is also shown that H(DMHP) is a more effective catalyst for the iron(iii) exchange reaction than bidentate hydroxamate chelators reported previously, supporting the hypothesis that chelator structure and iron(iii) affinity influence low denticity ligand facilitated catalysis of iron(iii) exchange reactions. The results are also discussed in the context of the design and use of combination chelator therapies in the treatment of Fe overload in humans.

Temporal variability of urinary cadmium in spot urine samples and first morning voids

Cadmium is a carcinogenic heavy metal. Urinary levels of cadmium are considered to be an indicator of long-term body burden, as cadmium accumulates in the kidneys and has a half-life of at least 10 years. However, the temporal stability of the biomarker in urine samples from a non-occupationally exposed population has not been rigorously established. We used repeated measurements of urinary cadmium (U-Cd) in spot urine samples and first morning voids from two separate cohorts, to assess the temporal stability of the samples. Urine samples from two cohorts including individuals of both sexes were measured for cadmium and creatinine. The first cohort (Home Observation of Perinatal Exposure (HOPE)) consisted of 21 never-smokers, who provided four first morning urine samples 2-5 days apart, and one additional sample roughly 1 month later. The second cohort (World Trade Center-Health Program (WTC-HP)) consisted of 78 individuals, including 52 never-smokers, 22 former smokers and 4 current smokers, who provided 2 spot urine samples 6 months apart, on average. Intra-class correlation was computed for groups of replicates from each individual to assess temporal variability. The median creatinine-adjusted U-Cd level (0.19 and 0.21 μg/g in the HOPE and WTC-HP, respectively) was similar to levels recorded in the United States by the National Health and Nutrition Examination Survey. The intra-class correlation (ICC) was high (0.76 and 0.78 for HOPE and WTC-HP, respectively) and similar between cohorts, irrespective of whether samples were collected days or months apart. Both single spot or first morning urine cadmium samples show good to excellent reproducibility in low-exposure populations.

A two-column flash chromatography approach to pyoverdin production from Pseudomonas putida GB1

Our knowledge of the biological and environmental reactivity of siderophores is limited by the difficulty and cost of obtaining reasonable quantities by purification or synthesis. In this note, we describe a modified procedure for the low-cost, mg-scale purification of pyoverdin-type siderophores using a dual-flash chromatography (reverse-phase absorption and size exclusion) approach.

Barriers and facilitators to initial and continued attendance at community-based lifestyle programmes among families of overweight and obese children: a systematic review

The success of childhood weight management programmes relies on family engagement. While attendance offers many benefits including the support to make positive lifestyle changes, the majority of families referred to treatment decline. Moreover, for those who do attend, benefits are often compromised by high programme attrition. This systematic review investigated factors influencing attendance at community-based lifestyle programmes among families of overweight or obese children. A narrative synthesis approach was used to allow for the inclusion of quantitative, qualitative and mixed-method study designs. Thirteen studies met the inclusion criteria. Results suggest that parents provided the impetus for programme initiation, and this was driven largely by a concern for their child's psychological health and wellbeing. More often than not, children went along without any real reason or interest in attending. Over the course of the programme, however, children's positive social experiences such as having fun and making friends fostered the desire to continue. The stigma surrounding excess weight and the denial of the issue amongst some parents presented barriers to enrolment and warrant further study. This study provides practical recommendations to guide future policy makers, programme delivery teams and researchers in developing strategies to boost recruitment and minimise attrition.

Characterization of Zinc Carbonate Basic as a Source of Zinc in a Rodent Study Investigating the Effects of Dietary Deficiency or Excess

Zinc deficiency and excess can result in adverse health outcomes. There is conflicting evidence regarding whether excess or deficient zinc in the diet can contribute to carcinogenicity. The objective of this study was to characterize zinc carbonate basic for use as a source of dietary zinc in a rodent toxicity and carcinogenicity study investigating the effects of zinc deficiency and excess. Because of the complex chemistries of zinc carbonate basic compounds, inconsistent nomenclature, and literature and reference spectra gaps, it was necessary to employ multiple analytical techniques, including Karl Fischer titration, combustion analysis, inductively coupled plasma-optical emission spectrometry, X-ray diffraction, infrared spectroscopy, X-ray fluorescence spectrometry, and thermogravimetric analysis to characterize the test article. Based on the collective evidence and through the process of elimination, the test article was found to be composed mainly of zinc carbonate basic with zinc oxide as a minor component. The zinc content was determined to be 56.6% (w/w) with heavy metals such as arsenic, cadmium, mercury and lead below the limit of quantitation of less than or equal to 0.01%. The test material was stable at ambient temperature. Based on the work described in this manuscript, the test article was suitable for use as a source of zinc in studies of deficiency and excess in the diet.

Disposition of intravenously or orally administered silver nanoparticles in pregnant rats and the effect on the biochemical profile in urine

Few investigations have been conducted on the disposition and fate of silver nanoparticles (AgNP) in pregnancy. The distribution of a single dose of polyvinylpyrrolidone (PVP)-stabilized AgNP was investigated in pregnant rats. Two sizes of AgNP, 20 and 110 nm, and silver acetate (AgAc) were used to investigate the role of AgNP diameter and particle dissolution in tissue distribution, internal dose and persistence. Dams were administered AgNP or AgAc intravenously (i.v.) (1 mg kg^-1 ) or by gavage (p.o.) (10 mg kg^-1 ), or vehicle alone, on gestation day 18 and euthanized at 24 or 48 h post-exposure. The silver concentration in tissues was measured using inductively-coupled plasma mass spectrometry. The distribution of silver in dams was influenced by route of administration and AgNP size. The highest concentration of silver (μg Ag g^-1 tissue) at 48 h was found in the spleen for i.v. administered AgNP, and in the lungs for AgAc. At 48 h after p.o. administration of AgNP, the highest concentration was measured in the cecum and large intestine, and for AgAc in the placenta. Silver was detected in placenta and fetuses for all groups. Markers of cardiovascular injury, oxidative stress marker, cytokines and chemokines were not significantly elevated in exposed dams compared to vehicle-dosed control. NMR metabolomics analysis of urine indicated that AgNP and AgAc exposure impact the carbohydrate, and amino acid metabolism. This study demonstrates that silver crosses the placenta and is transferred to the fetus regardless of the form of silver. Copyright © 2016 John Wiley & Sons, Ltd.

Quest to identify geochemical risk factors associated with chronic kidney disease of unknown etiology (CKDu) in an endemic region of Sri Lanka-a multimedia laboratory analysis of biological, food, and environmental samples

The emergence of a new form of chronic kidney disease of unknown etiology (CKDu) in Sri Lanka's North Central Province (NCP) has become a catastrophic health crisis. CKDu is characterized as slowly progressing, irreversible, and asymptomatic until late stages and, importantly, not attributed to diabetes, hypertension, or other known risk factors. It is postulated that the etiology of CKDu is multifactorial, involving genetic predisposition, nutritional and dehydration status, exposure to one or more environmental nephrotoxins, and lifestyle factors. The objective of this limited geochemical laboratory analysis was to determine the concentration of a suite of heavy metals and trace element nutrients in biological samples (human whole blood and hair) and environmental samples (drinking water, rice, soil, and freshwater fish) collected from two towns within the endemic NCP region in 2012 and 2013. This broad panel, metallomics/mineralomics approach was used to shed light on potential geochemical risk factors associated with CKDu. Based on prior literature documentation of potential nephrotoxins that may play a role in the genesis and progression of CKDu, heavy metals and fluoride were selected for analysis. The geochemical concentrations in biological and environmental media areas were quantified. Basic statistical measurements were subsequently used to compare media against applicable benchmark values, such as US soil screening levels. Cadmium, lead, and mercury were detected at concentrations exceeding US reference values in many of the biological samples, suggesting that study participants are subjected to chronic, low-level exposure to these elements. Within the limited number of environmental media samples, arsenic was determined to exceed initial risk screening and background concentration values in soil, while data collected from drinking water samples reflected the unique hydrogeochemistry of the region, including the prevalence of hard or very hard water, and fluoride, iron, manganese, sodium, and lead exceeding applicable drinking water standards in some instances. Current literature suggests that the etiology of CKDu is likely multifactorial, with no single biological or hydrogeochemical parameter directly related to disease genesis and progression. This preliminary screening identified that specific constituents may be present above levels of concern, but does not compare results against specific kidney toxicity values or cumulative risk related to a multifactorial disease process. The data collected from this limited investigation are intended to be used in the subsequent study design of a comprehensive and multifactorial etiological study of CKDu risk factors that includes sample collection, individual surveys, and laboratory analyses to more fully evaluate the potential environmental, behavioral, genetic, and lifestyle risk factors associated with CKDu.

Quest to identify geochemical risk factors associated with chronic kidney disease of unknown etiology (CKDu) in an endemic region of Sri Lanka-a multimedia laboratory analysis of biological, food, and environmental samples

The emergence of a new form of chronic kidney disease of unknown etiology (CKDu) in Sri Lanka's North Central Province (NCP) has become a catastrophic health crisis. CKDu is characterized as slowly progressing, irreversible, and asymptomatic until late stages and, importantly, not attributed to diabetes, hypertension, or other known risk factors. It is postulated that the etiology of CKDu is multifactorial, involving genetic predisposition, nutritional and dehydration status, exposure to one or more environmental nephrotoxins, and lifestyle factors. The objective of this limited geochemical laboratory analysis was to determine the concentration of a suite of heavy metals and trace element nutrients in biological samples (human whole blood and hair) and environmental samples (drinking water, rice, soil, and freshwater fish) collected from two towns within the endemic NCP region in 2012 and 2013. This broad panel, metallomics/mineralomics approach was used to shed light on potential geochemical risk factors associated with CKDu. Based on prior literature documentation of potential nephrotoxins that may play a role in the genesis and progression of CKDu, heavy metals and fluoride were selected for analysis. The geochemical concentrations in biological and environmental media areas were quantified. Basic statistical measurements were subsequently used to compare media against applicable benchmark values, such as US soil screening levels. Cadmium, lead, and mercury were detected at concentrations exceeding US reference values in many of the biological samples, suggesting that study participants are subjected to chronic, low-level exposure to these elements. Within the limited number of environmental media samples, arsenic was determined to exceed initial risk screening and background concentration values in soil, while data collected from drinking water samples reflected the unique hydrogeochemistry of the region, including the prevalence of hard or very hard water, and fluoride, iron, manganese, sodium, and lead exceeding applicable drinking water standards in some instances. Current literature suggests that the etiology of CKDu is likely multifactorial, with no single biological or hydrogeochemical parameter directly related to disease genesis and progression. This preliminary screening identified that specific constituents may be present above levels of concern, but does not compare results against specific kidney toxicity values or cumulative risk related to a multifactorial disease process. The data collected from this limited investigation are intended to be used in the subsequent study design of a comprehensive and multifactorial etiological study of CKDu risk factors that includes sample collection, individual surveys, and laboratory analyses to more fully evaluate the potential environmental, behavioral, genetic, and lifestyle risk factors associated with CKDu.

Validation of a Metallomics Analysis of Placenta Tissue by Inductively-Coupled Plasma Mass Spectrometry

Trace elements can play an important role in maternal health and fetal development, and deficiencies in some essential minerals including zinc and copper have been correlated in some individuals to the development of birth defects and adverse health outcomes later in life. The exact etiology of conditions like preeclampsia and the effects of fetal exposure to toxic metals has not been determined, making the assessment of trace element levels crucial to the elucidation of the causes of conditions like preeclampsia. Previous studies analyzing serum and placenta tissue have produced conflicting findings, suggesting the need for a robust, validated sample preparation and analysis method for the determination of trace elements in placenta. In this report, an acid digestion method and analysis by ICP-MS for a broad metallomics/mineralomics panel of trace elements is developed and validated over three experimental days for inter- and intraday precision and accuracy, linear range, matrix impact, and dilution verification. Spike recovery experiments were performed for the essential elements chromium (Cr), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn), and the toxic elements arsenic (As), cadmium (Cd), and lead (Pb) at levels equal to and in excess of native concentrations in control placenta tissue. The validated method will be essential for the development of scientific studies of maternal health and toxic metal exposure effects in childhood.

Dietary Intake Estimates and Urinary Cadmium Levels in Danish Postmenopausal Women

BACKGROUND

Cadmium is a known carcinogen that can disrupt endocrine signalling. Cigarette smoking and food are the most common routes of non-occupational exposure to cadmium. Cadmium accumulates in the kidney and can be measured in urine, making urine cadmium (U-Cd) a biomarker of long-term exposure. However dietary-cadmium (D-Cd) intake estimates are often used as surrogate indicator of cadmium exposure in non-smoking subjects. It is therefore important to investigate the concordance between D-Cd estimates obtained with Food Frequency Questionnaires and U-Cd.

METHODS

U-Cd levels were compared with estimated dietary-cadmium (D-Cd) intake in 1764 post-menopausal women from the Danish Diet, Cancer and Health cohort. For each participant, a food frequency questionnaire, and measures of cadmium content in standard recipes were used to judge the daily intake of cadmium, normalized by daily caloric intake. Cadmium was measured by ICP-MS in spot urine sampled at baseline and normalized by urinary creatinine. Information on diet, socio-demographics and smoking were self-reported at baseline.

RESULTS

Linear regressions between U-Cd and D-Cd alone revealed minimal but significant positive correlation in never smokers (R2 = 0.0076, β = 1.5% increase per 1 ng Cd kcal(-1), p = 0.0085, n = 782), and negative correlation in current smokers (R2 = 0.0184, β = 7.1% decrease per 1 ng Cd kcal(-1) change, p = 0.0006, n = 584). In the full study population, most of the variability in U-Cd was explained by smoking status (R2 = 0.2450, n = 1764). A forward selection model revealed that the strongest predictors of U-Cd were age in never smokers (Δ R2 = 0.04), smoking duration in former smokers (Δ R2 = 0.06) and pack-years in current smokers (Δ R2 = 0.07). Food items that contributed to U-Cd were leafy vegetables and soy-based products, but explained very little of the variance in U-Cd.

CONCLUSIONS

Dietary-Cd intake estimated from food frequency questionnaires correlates only minimally with U-Cd biomarker, and its use as a Cd exposure indicator may be of limited utility in epidemiologic studies.

Development, validation, and application of an ultra-performance liquid chromatography-sector field inductively coupled plasma mass spectrometry method for simultaneous determination of six organotin compounds in human serum

Organotin compounds (OTCs) are heavily employed by industry for a wide variety of applications, including the production of plastics and as biocides. Reports of environmental prevalence, differential toxicity between OTCs, and poorly characterized human exposure have fueled the demand for sensitive, selective speciation methods. The objective of this investigation was to develop and validate a rapid, sensitive, and selective analytical method for the simultaneous determination of a suite of organotin compounds, including butyl (mono-, di-, and tri-substituted) and phenyl (mono-, di-, and tri-substituted) species in human serum. The analytical method utilized ultra-performance liquid chromatography (UPLC) coupled with sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). The small (sub-2 µm) particle size of the UPLC column stationary phase and the sensitivity of the SF-ICP-MS enabled separation and sensitive determination of the analyte suite with a runtime of approximately 3 min. Validation activities included demonstration of method linearity over the concentration range of approximately 0.250-13.661 ng mL(-1), depending on the species; intraday precision of less than 21%, interday precision of less than 18%, intraday accuracy of -5.3% to 19%, and interday accuracy of -14% to 15% for all species; specificity, and matrix impact. In addition, sensitivity, and analyte stability under different storage scenarios were evaluated. Analyte stability was found to be limited for most species in freezer, refrigerator, and freeze-thaw conditions. The validated method was then applied for the determination of the OTCs in human serum samples from women participating in the Snart-Foraeldre/MiljØ (Soon-Parents/Environment) Study. The concentration of each OTC ranged from below the experimental limit of quantitation to 10.929 ng tin (Sn) mL(-1) serum. Speciation values were confirmed by a total Sn analysis.

Development of an analytical method for assessment of silver nanoparticle content in biological matrices by inductively coupled plasma mass spectrometry

Silver nanoparticles (AgNPs) are a broad class of synthetic nanoparticles that are utilized in a wide variety of consumer products as antimicrobial agents. Despite their widespread use, a detailed understanding of their toxicological characteristics and biological and environmental hazards is not available. To support research into the biodistribution and toxicology of AgNPs, it is necessary to develop a suitable method for the assessment of AgNP content in biological samples. Two methods were developed and validated to analyze citrate-coated AgNP content that utilize acid digestion of rodent feces and liver tissue samples, and a third method was developed for the dilution and direct analysis of rodent urine samples. Following sample preparation, the silver content of each sample was determined by inductively coupled plasma mass spectrometry (ICP-MS) to quantify the silver and AgNP levels present. Analysis of rat feces matrix yielded analytical recoveries ranging from 82 to 93 %. Liver tissue spiked with a formulation of AgNPs over a range of concentrations yielded analytical recoveries between 88 and 90 %, providing acceptable accuracy results. The analysis of silver in urine samples exhibited recovery values ranging from 80 to 85 % for AgNP formulations and 62-84 % for standard silver ion solutions. All determinations exhibited a high degree of analytical precision. The results obtained here suggest that matrix interference plays a minimal role in AgNP recovery in feces and liver tissue, while the urine matrix can exhibit a significant effect on the determination of silver content.

Analysis of human serum and whole blood for mineral content by ICP-MS and ICP-OES: development of a mineralomics method

Minerals are inorganic compounds that are essential to the support of a variety of biological functions. Understanding the range and variability of the content of these minerals in biological samples can provide insight into the relationships between mineral content and the health of individuals. In particular, abnormal mineral content may serve as an indicator of illness. The development of robust, reliable analytical methods for the determination of the mineral content of biological samples is essential to developing biological models for understanding the relationship between minerals and illnesses. This paper describes a method for the analysis of the mineral content of small volumes of serum and whole blood samples from healthy individuals. Interday and intraday precision for the mineral content of the blood (250 μL) and serum (250 μL) samples was measured for eight essential minerals--sodium (Na), calcium (Ca), magnesium (Mg), potassium (K), iron (Fe), zinc (Zn), copper (Cu), and selenium (Se)--by plasma spectrometric methods and ranged from 0.635 to 10.1% relative standard deviation (RSD) for serum and 0.348-5.98% for whole blood. A comparison of the determined ranges for ten serum samples and six whole blood samples provided good agreement with literature reference ranges. The results demonstrate that the digestion and analysis methods can be used to reliably measure the content of these minerals and potentially of other minerals.

The Affinity of Indium(III) for Nitrogen-donor Ligands in Aqueous Solution. A Study of the Complexing of Indium(III) with Polyamines by Differential Pulse Voltammetry, Density Functional Theory, and Crystallography

The affinity of In(III) for N-donor ligands was investigated by differential pulse voltammetry, DFT calculations, and crystallography. The structure of [In(tpen)(CH3COO)](ClO4)2 ・ 0.5H2O (1) is reported (tpen = N,N,N´ ,N´-tetrakis(2-pyridylmethyl)ethylenediamine): Monoclinic, P21/n, a = 8.687(4), b = 7.767(8), c = 20.432(10) Å , β = 93.372(8)°, Z = 4, R = 0.0518. The In(III) center is 7-coordinate, with six In-N bonds to the tpen ligand in the range 2.306 - 2.410 Å, and a unidentate acetate group with In-O = 2.247 Å. The formation constants of In3+ in 0.1 M NaNO3+ at 25 °C are (M = In(III), L = ligand, H = proton): L = triethylenetetramine, logβ (MLH2) = 25.3±}0.3, logK1 = 14.43±}0.09, and logβ (ML(OH)2) = 27.7±}0.1; tetraethylenepentamine, logβ (MLH) = 20.8±}0.2, and ML (logβ (ML) = 20.1±}0.3); diglycolic acid, (logβ (MLH) = 8.06±}0.06), logK1 = 6.02±} 0.06, logβ2 = 9.40±}0.08; tpen, logK1 = 17.71±}0.07; N,N´-bis(2-pyridylmethyl)ethylenediamine, logK1 = 14.69±}0.05; 1,10-phenanthroline, logK1 = 6.81±}0.07, logK2 = 6.44±}0.07, logK3 = 6.20±}0.08. Correlations are shown between the determined formation constants for the polyamines and logK1(NH3) values for a wide variety of metal ions. For M(II) ions, the log K1(NH3) values are experimental data, but for M(III) ions the data are predicted by an empirical dual-basicity equation, including logK1(NH3) = 4.0 for In(III). DFT calculations are used to obtain ΔE for the reaction [M(H2O)6]n+ + NH3 ⇆[M(H2O)5NH3]n+ + H2O for M(II) through M(IV) ions in water, represented as a structureless medium with the dielectric constant of water. Correlations are found that support the predicted value of logK1(NH3) for In(III) of 4.0. The nature of the intercepts on such correlations are discussed.

Evaluation of methods for analysis of lead in air particulates: an intra-laboratory and inter-laboratory comparison

In 2008, the United States Environmental Protection Agency (USEPA) set a new National Ambient Air Quality Standard (NAAQS) for lead in total suspended particulate matter (Pb-TSP) which called for significant decreases in the allowable limits. The Federal Reference Method (FRM) for Pb-TSP promulgated in 1978 prescribes analysis of Pb by flame atomic absorption spectroscopy (FAAS), but the new limits approach the limits of quantitation of FAAS. On August 2, 2013, the USEPA finalized a new FRM for Pb-TSP. This new FRM describes two extraction methods and analysis by inductively coupled plasma-mass spectrometry (ICP-MS). The study described here was performed to evaluate the use of ICP-MS in the analysis of Pb-TSP for implementation of this new FRM. A multi-laboratory study of the new FRM demonstrated acceptable intra- and inter-laboratory precision and comparability for glass fiber, quartz, and PTFE filters, and acceptable accuracy for the analysis of three National Institute of Standards and Technology (NIST) Standard Reference Materials (SRMs). A comparison was made between analytical results obtained using the 1978 FRM and those obtained using the new FRM. The results demonstrate that the ICP-MS method performs acceptably for the determination of Pb-TSP with lower limits of quantitation and strong inter- and intra-laboratory precision.

Rapid speciation and determination of vanadium compounds using ion-pair reversed-phase ultra-high-performance liquid chromatography inductively coupled plasma-sector field mass spectrometry

Environmental vanadium contamination is a potential concern to public health, as evidenced by its place on the U.S. Environmental Protection Agency Drinking Water Contaminant Candidate List as a priority contaminant. Vanadium toxicity varies significantly between different oxidation states; therefore, it is crucial to be able to monitor the speciation of vanadium in environmental samples. In this study, a novel method is described that utilizes ion-pair reversed-phase ultra-high-performance liquid chromatography with inductively coupled plasma-sector field mass spectrometry (IP-RP-UHPLC-ICP-SFMS) to separate vanadyl and vanadate ions and resolve a major polyatomic spectral interference ((35)Cl(16)O(+)) in less than a minute. Detection limits were obtained in the low ngL(-1) (part per trillion) range with linear calibrations across several orders of magnitude (50ngL(-1)-100μgL(-1)). The mechanism of chromatographic retention was elucidated through investigation of the role of ethylenediaminetetraacetic acid, tetrabutylammonium ion and pH on elution. The optimized method was then applied to the speciation of vanadium in local lake water samples.

Amelioration of metal-induced toxicity in Caenorhabditis elegans: utility of chelating agents in the bioremediation of metals

The presence of toxic amounts of transition metals in the environment may originate from a range of human activities and natural processes. One method for the removal of toxic levels of metals is through chelation by small molecules. However, chelation is not synonymous with detoxification and may not affect the bioavailability of the metal. To test the bioavailability of chelated metals in vivo, the effects of several metal/chelator combinations were tested in the environmentally relevant organism Caenorhabditis elegans. The effect of metal exposure on nematode growth was used to determine the toxicity of cadmium, copper, nickel, and zinc. The restoration of growth to levels observed in nonexposed nematodes was used to determine the protective effects of the polydentate chelators: acetohydroxamic acid (AHA), cyclam, cysteine, calcium EDTA, desferrioxamine B, 1,2-dimethyl,3-hydroxy,4-pyridinone, and histidine. Cadmium toxicity was removed only by EDTA; copper toxicity was removed by all of the chelators except AHA; nickel toxicity was removed by cyclam, EDTA, and histidine; and zinc toxicity was removed by only EDTA. These results demonstrate the utility of polydentate chelators in the remediation of metal-contaminated systems. They also demonstrate that although the application of a chelator to metal contaminants may be effective, binding alone cannot be used to predict the level of remediation. Remediation depends on a number of factors, including metal complex speciation in the environment.

Trace metal complexation by the triscatecholate siderophore protochelin: structure and stability

Although siderophores are generally viewed as biological iron uptake agents, recent evidence has shown that they may play significant roles in the biogeochemical cycling and biological uptake of other metals. One such siderophore that is produced by A. vinelandii is the triscatecholate protochelin. In this study, we probe the solution chemistry of protochelin and its complexes with environmentally relevant trace metals to better understand its effect on metal uptake and cycling. Protochelin exhibits low solubility below pH 7.5 and degrades gradually in solution. Electrochemical measurements of protochelin and metal-protochelin complexes reveal a ligand half-wave potential of 200 mV. The Fe(III)Proto(3-) complex exhibits a salicylate shift in coordination mode at circumneutral to acidic pH. Coordination of Mn(II) by protochelin above pH 8.0 promotes gradual air oxidation of the metal center to Mn(III), which accelerates at higher pH values. The Mn(III)Proto(3-) complex was found to have a stability constant of log β(110) = 41.6. Structural parameters derived from spectroscopic measurements and quantum mechanical calculations provide insights into the stability of the Fe(III)Proto(3-), Fe(III)H(3)Proto, and Mn(III)Proto(3-) complexes. Complexation of Co(II) by protochelin results in redox cycling of Co, accompanied by accelerated degradation of the ligand at all solution pH values. These results are discussed in terms of the role of catecholate siderophores in environmental trace metal cycling and intracellular metal release.