Formation of organic chloramines during water disinfection - chlorination versus chloramination

Many of the available studies on formation of organic chloramines during chlorination or chloramination have involved model organic nitrogen compounds (e.g., amino acids), but not naturally occurring organic nitrogen in water. This study assessed organic chloramine formation during chlorination and chloramination of 16 natural organic matter (NOM) solutions and 16 surface waters which contained dissolved organic nitrogen (DON). Chlorination rapidly formed organic chloramines within 10 min, whereas chloramination formed organic chloramination much more slowly, reaching the maximum concentration between 2 and 120 h after the addition of monochloramine into the solutions containing DON. The average organic chloramine formation upon addition of free chlorine and monochloramine into the NOM solutions were 0.78 mg-Cl₂/mg-DON at 10 min and 0.16 mg-Cl₂/mg-DON at 24 h, respectively. Organic chloramine formation upon chlorination and chloramination increased as the dissolved organic carbon/dissolved organic nitrogen (DOC/DON) ratio decreased (i.e., DON contents increased). Chlorination of molecular weight (10,000 Da) fractionated water showed that molecular weight of DON would not impact the amount of organic chloramines produced. Comparison of three different disinfection schemes at water treatment plants (free chlorine, preformed monochloramine, and chlorine/ammonia additions) indicated organic chloramine formation could lead to a possible overestimation of disinfection capacity in many chloraminated water systems that add chlorine followed by an ammonia addition to form monochloramine.     

Effect of free ammonia concentration on monochloramine penetration within a nitrifying biofilm and its effect on activity, viability, and recovery

Chloramine has replaced free chorine for secondary disinfection at many water utilities because of disinfection by-product (DBP) regulations. Because chloramination provides a source of ammonia, there is a potential for nitrification when using chloramines. Nitrification in drinking water distribution systems is undesirable and may result in degradation of water quality and subsequent non-compliance with existing regulations. Thus, nitrification control is a major issue and likely to become increasingly important as chloramine use increases. In this study, monochloramine penetration and its effect on nitrifying biofilm activity, viability, and recovery was investigated and evaluated using microelectrodes and confocal laser scanning microscopy (CLSM). Monochloramine was applied to nitrifying biofilm for 24 h at two different chlorine to nitrogen (Cl₂:N) mass ratios (4:1 [4.4 mg Cl₂/L] or 1:1 Cl₂:N [5.3 mg Cl₂/L]), resulting in either a low (0.23 mg N/L) or high (4.2 mg N/L) free ammonia concentration. Subsequently, these biofilm samples were allowed to recover without monochloramine and receiving 4.2 mg N/L free ammonia. Under both monochloramine application conditions, monochloramine fully penetrated into the nitrifying biofilm within 24 h. Despite this complete monochloramine penetration, complete viability loss did not occur, and both biofilm samples subsequently recovered aerobic activity when fed only free ammonia. When monochloramine was applied with a low free ammonia concentration, dissolved oxygen (DO) fully penetrated, but with a high free ammonia concentration, complete cessation of aerobic activity (i.e., oxygen utilization) did not occur and subsequent analysis indicated that oxygen consumption still remained near the substratum. During the ammonia only recovery phase, different spatial recoveries were seen in each of the samples, based on oxygen utilization. It appears that the presence of higher free ammonia concentration allowed a larger biomass to remain active during monochloramine application, particularly the organisms deeper within the biofilm, leading to faster recovery in oxygen utilization when monochloramine was removed. These results suggest that limiting the free ammonia concentration during monochloramine application will slow the onset of nitrification episodes by maintaining the biofilm biomass at a state of lower activity.     

Effect of some parameters on the formation of chloroform during chloramination of aqueous solutions of resorcinol

The effects of various factors (N/Cl ratio used to prepare monochloramine, monochloramine doses, pH and contact time) on the monochloramine demand and on the chloroform yield during chloramination of resorcinol have been investigated. Chloramination experiments were carried out at 24 ± 1 °C, at pH values ranging from 6.5 to 12 using a bicarbonate/carbonate buffer and preformed monochloramine solutions prepared at pH 8.5 with N/Cl ratios ([NH₄Cl]₀/[Total free Cl₂]₀ ranging from 1.0 to 150 mol/mol). Kinetic experiments ([Resorcinol]₀ = 5 or 100 μM, [NH₂Cl]₀/[Resorcinol]₀ = 20 mol/mol, pH = 8.5 ± 0.1) showed a slow increase of the monochloramine consumption with reaction time. The monochloramine demands after reaction times of 7 days ([Resorcinol]₀ = 100 μM) and 14 days ([Resorcinol]₀ = 5 μM) were equal to 8.5 mol of NH₂Cl/mole of resorcinol and were higher than the chlorine demands (≈7.3 mol/mol). Chloroform yields from monochloramination of resorcinol were lower than 8% (<80 mmol of CHCl₃/mole of resorcinol) and were less than the yields obtained by chlorination (0.9-0.95 mol/mol). Chloroform productions increased with increasing monochloramine dose and reaction time and decreased with increasing pH values within the pH range 6.5-10. Chloroform formation markedly decreased when the N/Cl ratio increased from 1 to 1.5 mol/mol and was suppressed at N/Cl > 100 mol/mol. The data obtained in the present work suggest that free chlorine released from monochloramine hydrolysis plays a significant role on the formation of chloroform during chloramination of resorcinol at N/Cl ratios close to unity (1.0 < N/Cl < 1.5).     

Whole blood mercury and selenium concentrations in a selected Austrian population: does gender matter?

Background

Data on mercury exposure of the Austrian population were inadequate. This study was performed to determine the causal factors underlying mercury exposure and selenium concentrations, and to estimate the gender-related health impacts.

Methodology

Venous blood samples of 78 women and 81 men were drawn at the Austrian Red Cross, Vienna. Mercury contents in acid-digested whole blood samples were measured after amalgam enrichment by CV-AAS, and selenium by AAS (heated quartz-cell) after hydrid formation.

Results

The average total mercury blood content of Austrians was low (2.38 ± 1.55 μgL^− 1; N = 152). Mercury and selenium concentrations were not different between the genders (P > 0.05) but we observed discrepancies regarding the causal factors. Mercury levels in men were influenced not only by fish consumption but also by age, education level, and amalgam fillings, whereas in women, only the diet (fish/seafood, red wine consumption) determined blood mercury (P < 0.05). Moreover, only the males indicated a depressive effect of dental amalgam on hematocrit (P < 0.05). Regarding selenium, age and alcohol consumption led to lower concentrations in men, whereas a high-level education had the opposite effect; no determinant was found for women. For the whole study group, a significant effect of chronic disease on selenium levels could be detected (P < 0.05). 18% of women and 13% of men showed marginal selenium deficiency (blood selenium < 65 μgL^− 1). Selenium and mercury concentrations were not correlated.

Conclusions

Our results indicate the need to evaluate and integrate gender-related findings in metal toxicology and trace element research, because different causal factors require different preventive measures to reduce mercury exposure and the risk of low selenium concentrations. Future research is needed on the gender- and age-related differences in fish/seafood consumption habits, the modifications of mercury toxicokinetics through sex hormones, the selenium supply in Austria, and the clinical relevance of a low selenium status.     

Blood total mercury and fish consumption in the Korean general population in KNHANES III, 2005

Objectives

The obejective of this study was to assess the association between the blood total mercury concentration and fish consumption in the Korean general adult population using a representative sample.

Methods

We studied the blood mercury concentration in a representative sample of 1,749 Koreans who were included in the Third Korean National Health and Nutritional Examination Survey (KNHANES III) performed in 2005, and compared it with the frequency of fish consumption collected during the nutrition survey of KNHANES III.

Results

The geometric means of the blood mercury levels in female subjects (n = 890), male subjects (n = 859), and all participants (n = 1,749) representing adult Koreans aged ≥ 20 years were 3.70 μg/L [95% confidence interval (CI), 3.46-3.94 μg/L], 4.70 μg/L (95% CI, 4.38-5.02 μg/L), and 4.15 μg/L (95% CI, 3.93-4.38 μg/L), respectively. The geometric mean of the blood mercury level was significantly higher in the high-fish-consumption group (4.38 μg/L; more than once a week) than in the low-consumption group (3.71 μg/L: less than once a week), but the intergroup difference of 18% was less than that in Western countries. Among the nine listed individual types of fish and shellfish, there was a general trend for the blood mercury level to increase with the consumption frequency of squid, clam, salted seafood, and mackerel. The proportion of Korean women aged 20-49 years having blood mercury levels of at least 5.8 μg/L was 27.7% (150/542) in our study.

Conclusions

The blood mercury level in a representative sample of the Korean adult population was found to be associated with fish consumption in both men and women. However, a high consumption of fish increased the blood mercury level by only 18%.     

Modeling monochloramine loss in the presence of natural organic matter

A comprehensive model describing monochloramine loss in the presence of natural organic matter (NOM) is presented. The model incorporates simultaneous monochloramine autodecomposition and reaction pathways resulting in NOM oxidation. These competing pathways were resolved numerically using an iterative process evaluating hypothesized reactions describing NOM oxidation by monochloramine under various experimental conditions. The reaction of monochloramine with NOM was described as biphasic using four NOM specific reaction parameters. NOM pathway 1 involves a direct reaction of monochloramine with NOM (k_doc1=1.05×10⁴-3.45×10⁴ M⁻¹ h⁻¹). NOM pathway 2 is slower in terms of monochloramine loss and attributable to free chorine (HOCl) derived from monochloramine hydrolysis (k_doc2=5.72×10⁵-6.98×10⁵ M⁻¹ h⁻¹), which accounted for the majority of monochloramine loss. Also, the free chlorine reactive site fraction in the NOM structure was found to correlate to specific ultraviolet absorbance at 280 nm (SUVA₂₈₀). Modeling monochloramine loss allowed for insight into disinfectant reaction pathways involving NOM oxidation. This knowledge is of value in assessing monochloramine stability in distribution systems and reaction pathways leading to disinfection by-product (DBP) formation.     

Association and decontamination of Bacillus spores in a simulated drinking water system

The objective of this work was to elucidate the disinfectant susceptibility of Bacillus anthracis Sterne (BA) and a commercial preparation of Bacillus thuringiensis (BT) spores associated with a simulated drinking water system. Biofilms composed of indigenous water system bacteria were accumulated on copper and polyvinyl chloride (PVC) pipe material surfaces in a low-flow pipe loop and uniformly mixed tank reactor (CDC biofilm reactor). Application of a distributed shear during spore contact resulted in approximately a 1.0 and 1.6 log₁₀ increase in the number of spores associated with copper and PVC surfaces, respectively. Decontamination of spores in both free suspension and after association with biofilm-conditioned pipe materials was attempted using free chlorine and monochloramine. Associated spores required 5- to 10-fold higher disinfectant concentrations to observe the same reduction of viable spores as in suspension. High disinfectant concentrations (103 mg/L free chlorine and 49 mg/L monochloramine) yielded less than a 2-log₁₀ reduction in viable associated spores after 60 min. Spores associated with biofilms on copper surfaces consistently yielded higher Ct values than PVC.     

Mercury (Hg) burden in children: the impact of dental amalgam

The risks and benefits of using mercury (Hg) in dental amalgam have long been debated. This study was designed to estimate Hg body burden and its association with dental amalgam fillings in 182 children (ages: 5-15 years) living in Taif City. Hg was measured in urine (UHg), hair (HHg) and toenails (NHg) by the Atomic Absorption Spectrophotometer with Vapor Generator Accessory system. Urinary Hg levels were calculated as both micrograms per gram creatinine (μg/g creatinine) and micrograms per liter (μg/L). We found that children with amalgam fillings (N = 106) had significantly higher UHg-C levels than children without (N = 76), with means of 3.763 μg/g creatinine versus 3.457 μg/g creatinine, respectively (P = 0.019). The results were similar for UHg (P = 0.01). A similar pattern was also seen for HHg, with means of 0.614 μg/g (N = 97) for children with amalgam versus 0.242 μg/g (N = 74) for those without amalgam fillings (P = 0). Although the mean NHg was higher in children without amalgam (0.222 μg/g, N = 61) versus those with (0.163 μg/g, N = 101), the relationship was not significant (P = 0.069). After adjusting for many confounders, the multiple logistic regression model revealed that the levels of UHg-C and HHg were 2.047 and 5.396 times higher, respectively, in children with dental amalgam compared to those without (P < 0.01). In contrast, a significant inverse relationship was seen between NHg levels and dental amalgam fillings (P = 0.003). Despite the controversy surrounding the health impact of dental amalgam, this study showed some evidence that amalgam-associated Hg exposure might be related with symptoms of oral health, such as aphthous ulcer, white patches, and a burning-mouth sensation. Further studies are needed to reproduce these findings. The present study showed that significant numbers of children with or without amalgam had Hg levels exceeding the acceptable reference limits. The detrimental neurobehavioral and/or nephrotoxic effects of such an increased Hg on children should be a cause of concern, and further investigation is warranted. Our results are alarming and indicate an urgent need for biomonitoring and assessment of exposure. Changes in dental practices involving amalgam, especially for children, are highly recommended in order to avoid unnecessary exposure to Hg.     

The correlation of arsenic levels in drinking water with the biological samples of skin disorders

Arsenic (As) poisoning has become a worldwide public health concern. The skin is quite sensitive to As and skin lesions are the most common and earliest nonmalignant effects associated to chronic As exposure. In 2005-2007, a survey was carried out on surface and groundwater arsenic contamination and relationships between As exposure via the drinking water and related adverse health effects (melanosis and keratosis) on villagers resides on the banks of Manchar lake, southern part of Sindh, Pakistan. We screened the population from arsenic-affected villages, 61 to 73% population were identified patients suffering from chronic arsenic toxicity. The effects of As toxicity via drinking water were estimated by biological samples (scalp hair and blood) of adults (males and females), have or have not skin problem (n = 187). The referent samples of both genders were also collected from the areas having low level of As (< 10 μg/L) in drinking water (n = 121). Arsenic concentration in drinking water and biological samples were analyzed using electrothermal atomic absorption spectrometry. The range of arsenic concentrations in lake surface water was 35.2-158 μg/L, which is 3-15 folds higher than World Health Organization [WHO, 2004. Guidelines for drinking-water quality third ed., WHO Geneva Switzerland.]. It was observed that As concentration in the scalp hair and blood samples were above the range of permissible values 0.034-0.319 μg As/g for hair and < 0.5-4.2 μg/L for blood. The linear regressions showed good correlations between arsenic concentrations in water versus hair and blood samples of exposed skin diseased subjects (R² = 0.852 and 0.718) as compared to non-diseased subjects (R² = 0.573 and 0.351), respectively.     

Mercury exposure assessment in Iranian women's hair of a port town with respect to fish consumption and amalgam fillings

In this study we aimed to estimate the level of mercury in women's hair and its association with fish consumption and amalgam fillings in an Iranian southern port town (named Mahshahr). A total number of 195 hair samples were collected randomly from women aged 25-45 years free from occupational exposures to mercury. Additional information about these women's age, weight, height, number of pregnancies, level of education, number of amalgam fillings and fish consumption were also gathered. The determination of Hg level in hair samples was carried out by the LECO, AMA 254, Advanced Mercury Analyzer, according to ASTM standard No. D-6722. The average mercury level in these women's hair was 2.95 ± 2.33 µg/g (ranged from 0.07 to 24.46 µg/g). In the next stage, the study participants were divided into four groups with respect to their fish consumption and number of amalgam fillings; A) < 3 amalgam fillings, < 3 times fish consumption per month, B) < 3 amalgam fillings, > 7 times fish consumption per month, C) > 6 amalgam fillings, < 3 times fish consumption per month, and D) > 6 amalgam fillings, > 7 times fish consumption per month. Statistical analysis showed that the Hg level was significantly different in these four groups (P < 0.001). Mercury levels in this sample exceeded the USEPA-recommended 1 μg/g in 76.4% of the studied population. Finally, the multiple linear regression results revealed that frequency of fish consumption and amalgam restorations are the most important routes of Hg exposure. However, the main determinant of Hg exposure was the intake of Hg through fish consumption.     

Feather mercury concentrations and physiological condition of great egret and white ibis nestlings in the Florida Everglades

Mercury contamination in the Florida Everglades has reportedly played a role in the recent decline of wading birds, although no studies have identified a mechanism leading to population-level effects. We assessed feather mercury levels in great egret (Ardea alba; n = 91) and white ibis (Eudocimus albus; n = 46) nestlings at breeding colonies in the Florida Everglades during a year (2006) with excellent breeding conditions (characterized by hydrology leading to concentrated prey) and a year with below average breeding conditions (2007). We also assessed the physiological condition of those nestlings based on levels of plasma and fecal corticosterone metabolites, and stress proteins 60 and 70. Mercury levels were higher in both species during the good breeding condition year (great egret = 6.25 μg/g ± 0.81 SE, white ibis = 1.47 μg/g ± 0.41 SE) and lower in the below average breeding year (great egret = 1.60 μg/g ± 0.11 SE, white ibis = 0.20 μg/g ± 0.03 SE). Nestlings were in better physiological condition in 2006, the year with higher feather mercury levels. These results support the hypothesis that nestlings are protected from the harmful effects of mercury through deposition of mercury in growing feathers. We found evidence to suggest shifts in diets of the two species, as a function of prey availability, thus altering their exposure profiles. However, we found no evidence to suggest they respond differently to mercury exposure.     

Assessment of the removal and inactivation of influenza viruses H5N1 and H1N1 by drinking water treatment

Since 2003, there has been significant concern about the possibility of an outbreak of avian influenza virus subtype H5N1. Moreover, in the last few months, a pandemic of a novel swine-origin influenza A virus, namely A(H1N1), has already caused hundreds of thousands of human cases of illness and thousands of deaths. As those viruses could possibly contaminate water resources through wild birds excreta or through sewage, the aim of our work was to find out whether the treatment processes in use in the drinking water industry are suitable for eradicating them. The effectiveness of physical treatments (coagulation-flocculation-settling, membrane ultrafiltration and ultraviolet) was assessed on H5N1, and that of disinfectants (monochloramine, chlorine dioxide, chlorine, and ozone) was established for both the H5N1 and H1N1 viruses.Natural water samples were spiked with human H5N1/H1N1 viruses. For the coagulation-settling experiments, raw surface water was treated in jar-test pilots with 3 different coagulating agents (aluminum sulfate, ferric chloride, aluminum polychorosulfate). Membrane performance was quantified using a hollow-fiber ultrafiltration system. Ultraviolet irradiation experiments were conducted with a collimated beam that made it possible to assess the effectiveness of various UV doses (25-60 mJ/cm²). In the case of ozone, 0.5 mg/L and 1 mg/L residual concentrations were tested with a contact time of 10 min. Finally, for chlorine, chlorine dioxide and monochloramine treatments, several residual oxidant target levels were tested (from 0.3 to 3 mg/L) with contact times of 5-120 min. The infectivity of the H5N1 and H1N1 viruses in water samples was quantified in cell culture using a microtiter endpoint titration.The impact of coagulation-settling on the H5N1 subtype was quite low and variable. In contrast, ultrafiltration achieved more than a 3-log reduction (and more than a 4-log removal in most cases), and UV treatment was readily effective on its inactivation (more than a 5-log inactivation with a UV dose of 25 mJ/cm²). Of the chemical disinfection treatments, ozone, chlorine and chlorine dioxide were all very effective in inactivating H5N1 and H1N1, whereas monochloramine treatment required higher doses and longer contact times to achieve significant reductions.Our findings suggest that the water treatment strategies that are currently used for surface water treatment are entirely suitable for removing and/or inactivating influenza A viruses. Appropriate preventive actions can be defined for single disinfection treatment plants.     

Occupational and environmental mercury exposure among small-scale gold miners in the Talensi-Nabdam District of Ghana's Upper East region

Mercury use in small-scale gold mining is ubiquitous across Ghana but little is known about the extent to which such activities have contaminated community residents and miners. Here, occupational exposures to elemental mercury (via urine sampling) and dietary exposures to methylmercury (via hair sampling) were assessed among 120 participants recruited from a mining community located in the Talensi-Nabdam District of Ghana's Upper East region during summer 2009. More than one-fifth of the participants had moderately high levels of urinary mercury (> 10 μg/L) and 5% had urine mercury levels that exceeded the WHO guideline value of 50 μg/L. When participants were stratified according to occupation, those active in the mining industry had the highest mercury levels. Specifically, individuals that burned amalgam had urine mercury levels (median: 43.8 μg/L; mean ± SD: 171.1 ± 296.5 μg/L; n = 5) significantly higher than median values measured in mechanical operators (11.6 μg/L, n = 4), concession managers/owners (5.6 μg/L, n = 11), excavators that blast and chisel ore (4.9 μg/L, n = 33), individuals that sift and grind crushed ore (2.2 μg/L, n = 47), support workers (0.5 μg/L, n = 14), and those with no role in the mining sector (2.5 μg/L, n = 6). There was a significant positive Spearman correlation between fish consumption and hair mercury levels (r = 0.30) but not with urine mercury (r = 0.18) though further studies are needed to document which types of fish are consumed as well as portion sizes. Given that 200,000 people in Ghana are involved in the small-scale gold mining industry and that the numbers are expected to grow in Ghana and many other regions of the world, elucidating mercury exposure pathways in such communities is important to help shape policies and behaviors that may minimize health risks.     

Identification of potential nitrogenous organic precursors for C-, N-DBPs and characterization of their DBPs formation

Nitrosamines are a class of emerging disinfection by-products (DBPs), which are mainly formed when water is treated by chloramination. Nitrosamines are highly carcinogenic and are hence a major concern for drinking water supplies. Although dissolved organic nitrogen (DON) compounds such as dimethylamine (DMA) have been recognized as important precursors of nitrosamines, many of them have not been identified, especially those used in consumer products. In this study, nine representative nitrogenous organic compounds with different DON characteristics and structures were selected to react with free chlorine, chlorine dioxide and monochloramine, respectively, for their DBP formation characteristics (nitrosamines, trihalomethanes (THMs) and haloacetic acids (HAAs)). It was found that in addition to DMA, benzyldimethyltetradecylamine (benzalkonium chloride, BKC) and 3-(N,N-dimethyloctyl-ammonio)propanesulfonate (3-N,N-DAPSIS) inner salt were potent precursors for carbonated DBPs (C-DBPs) and nitrogenated DBPs (N-DBPs). The DBP formation potential (DBPFP) tests showed that 1 mM of BKC formed more than 2 × 10⁵ ng/L of N-nitrosodimethylamine (NDMA) when treated with monochloramine and high levels of C-DBPs (2713 ± 145 μg/L of THMs and 356 ± 5 μg/L of HAAs) when treated with chlorine. 3-N,N-DAPSIS was a less potent DBP precursor: 1 mM of 3-N,N-DAPSIS generated 1155 ± 7 ng/L of NDMA, 1351 ± 66 μg/L of THMs and 188 ± 1 μg/L of HAAs. DMA, 3-N,N-DAPSIS and BKC were examined for their DBPFPs at various pH and temperatures to determine the impact of pH and reaction temperature on DBP yields and their formation mechanisms. The results showed that DBP yields apparently increased with rising temperature. However, no consistent correlations were observed between DBPs yields and pH. Bromide shifted the DBP species into brominated DBPs, and this phenomenon was more apparent when BKC was treated with chloramine.     

氯胺消毒工艺中一氯胺生成效率的影响规律

以上海市某自来水厂滤后水为研究对象,系统考察了氯胺消毒过程中氮源种类、氯氮比、pH值、反应时间、温度、G值和氯投加速率等因素对一氯胺浓度及消毒副产物(DBPs)生成量的影响。结果表明,氮源种类、Cl₂/N质量比和p H值为主要影响因素,其他为次要影响因素。与氯化铵、碳酸铵、醋酸铵和氨水这4种氮源相比,以硫酸铵为氮源可生成较高浓度的一氯胺;当pH值由6.0增大到9.0时,一氯胺浓度(以Cl₂计)由2.611 mg/L升高至4.256 mg/L;随着Cl₂/N质量比由2∶1逐渐增至8∶1,一氯胺浓度先升后降,并在5∶1时达到最大值3.831 mg/L。DBPs浓度随Cl₂/N质量比、反应时间、温度和氯投加速率的增加而升高,随G值的增大而降低;而随着pH值由6.0增加到9.0,DBPs浓度先降低后略有增加。自来水厂氯胺消毒工艺中一氯胺生成的最佳工艺条件如下:以硫酸铵为氮源,Cl₂/N质量比为(4∶1)~(5∶1),pH值为中性或碱性,反应时间为2 h,温度为25℃左右,G值为300 s-1,混匀慢速加氯。     

Sediment mercury dynamics and historical trends of mercury deposition in the St. Lawrence River area of concern near Cornwall, Ontario, Canada

The St. Lawrence River near Cornwall, Ontario was designated an Area of Concern by the International Joint Commission in 1985. Sediments from this area have historically been contaminated with mercury (Hg), and although concentrations have decreased since the 1970s, they still remain high. Nine sediment cores were collected from three sites within the Area of Concern in 2004/05 to determine the variability in historical profiles of Hg deposition to the river. Sediment and pore water phases were analyzed for total mercury (THg) and methyl mercury (MeHg) and cores were analyzed for ²¹⁰Pb to determine chronologies of sedimentation at these sites. Mercury diffusion rates in pore waters within the sediment column were determined to be very low (between 0 and 2.15 ng cm^− 2 year^− 1, n = 3) compared to the recent Hg sedimentation rates at these sites (183 ± 30 ng cm^− 2 year^− 1 SE, n = 9) determined by multiplying surface Hg concentrations with ²¹⁰Pb-derived sedimentation rates. These results indicate that Hg profiles in these cores accurately depict historical releases of Hg to the river bed. The influence of federal regulations in the early 1970s to restrict Hg emissions to the river was apparent in these dated sediment cores, as were the closures of several local industries in the mid 1990s. Mercury accumulation rates prior to 1970 were 60 times higher than those occurring after 1995. Methyl mercury showed surface enrichment in most of these sediment cores providing evidence that mercury methylation occurred most rapidly near the sediment surface.     

Mercury bioacumulation in four tissues of Podocnemis erythrocephala (Podocnemididae: Testudines) as a function of water parameters

A number of environmental factors influence the dynamics of Hg in aquatic ecosystems, yet few studies have examined these factors for turtles, especially from South America. Red-headed river turtle (Podocnemis erythrocephala) is easy to capture in the black waters of Rio Negro, making it the turtle species that is consumed most often by people of the region. In this study, environmental factors and turtle size were investigated to determine their influence on the Hg concentration in blood, muscle, liver and carapace of the red-headed river turtle. Factors investigated included turtle length, pH, dissolved organic carbon and availability of potential methylation sites (floodplain forests and hydromorphic soils). The study was conducted in the Rio Negro basin, where we collected water and turtle blood, muscle, liver and carapace samples from 12 tributaries for chemical analysis. Through radar imagery and existing soil maps with GIS, the percentage of alluvial floodplains and hydromorphic soils (potential methylation sites) was estimated for each drainage basin at sampling points. The mean Hg concentration in blood of P. erythrocephala was 1.64 ng g^− 1 (SD = 1.36), muscle 33 ng g^− 1 (SD = 11), liver 470 ng g^− 1 (SD = 313) and carapace 68 ng g^− 1 (SD = 32). Sex or length did not influence the Hg concentration in P. erythrocephala blood, muscle and liver, but Hg increased in carapace tissue when length size increased (ANCOVA p = 0.007). In the multiple regression analysis, none of the environmental factors studied had a significant relation with blood, muscle, liver and carapace. P. erythrocephala moves among habitats and in the open and interconnected aquatic systems of the Amazon basin, characterized by high levels of limnological variability, a good bioindicator of Hg concentration needs to be relatively sedentary to represent a specific habitat. However, the levels of Hg in liver were sufficient to pose a potential risk to humans that consume them, suggesting the usefulness of P. erythrocephala as a bioindicator.     

Mercury contamination in the vicinity of a chlor-alkali plant and potential risks to local population

A mercury-cell chlor-alkali plant operated in Estarreja (North-western Portugal) for 50 years causing widespread environmental contamination. Although production by this process ceased in 2002, mercury contamination from the plant remains significant. The main objective of this study was to investigate mercury impact on the nearby environment and potential risks to local population. To assess the level of contamination soil samples were collected from agricultural fields in the vicinity of the plant, extending the study by taking samples of the predominant vegetation suitable for animal and human consumption, water samples, and fish species from a nearby coastal lagoon, to gain a preliminary insight into the potential for contamination of the terrestrial and aquatic food web. To determine population exposure to mercury, hair samples were collected from local residents. Total mercury concentration in the 0-15 cm layer of soil was found to be highly variable, ranging between 0.010 and 91 mg kg^− 1, although mercury contamination of soils was found to be restricted to a confined area. Lolium perenne roots contained between 0.0070 and 2.0 mg kg^− 1, and there is evidence that root systems uptake mercury from the soil. Levels of mercury in the aerial parts of plants ranged between 0.018 and 0.98 mg kg^− 1. It appears that plants with higher mercury concentration in soils and roots also display higher mercury concentration in leaves.Total mercury concentration in water samples ranged between 12 and 846 ng L^− 1, all samples presenting concentrations below the maximum level allowable for drinking water defined in the Portuguese law (1.0 μg L^− 1).Mercury levels in fish samples were below the maximum limit defined in the Portuguese law (0.5 mg kg^− 1), ranging from 0.0040 to 0.24 mg kg^− 1. Vegetables collected presented maximum mercury concentration of 0.17 mg kg^− 1. In general, food is not contaminated and should not be responsible for major human exposure to the metal.Mercury determined in human hair samples (0.090-4.2 mg kg^− 1; mean 1.5 mg kg^− 1) can be considered within normal limits, according to WHO guidelines suggesting that it is not affecting the local population. Despite being subject to decades of mercury emissions, nowadays this pollutant is only found in limited small areas and must not constitute a risk for human health, should these areas be restricted and monitored.Considering the present data, it appears that the population from Estarreja is currently not being affected by mercury levels that still remain in the environment.     

Some physiological responses of rainbow trout (Salmo gairdneri) to intermittent monochloramine exposure

Rainbow trout (Salmo gairdneri) were exposed for 2.5 h to monochloramine (NH₂Cl) at an average concentration of 0.16 or 0.23 mg l⁻¹ (and with peak concentrations of 0.4 or 0.6 mg l⁻¹) three times daily. This simulates conditions in the outfall area of many electric power plants. Heart rate, opercular movement, cough frequency, arterial PO₂, lactate, hemoglobin and methemoglobin were monitored. The trout responded to chloramine pulses with slight increases in opercular movement, bradycardia, and a large increase in cough rate. These factors approached control rates between periods of exposure to a peak concentration of 0.4 mg l⁻¹, but not when the peak was 0.6 mg l⁻¹. Neither hemoglobin or lactate changed, while arterial PO₂ decreased slightly but not significantly. Methemoglobin concentration increased markedly at the end of each period of exposure with some recovery between them. In contrast to free chlorine, which causes acute hypoxemia due to gill damage, chloramine at these concentrations causes little if any hypoxemia. The elevated methemoglobin levels, not seen following exposure to free chlorine, indicate that perhaps chloramine is entering the blood stream to an extent that does not occur with free chlorine. Methemoglobinemia is probably not the proximate cause of death.     

Combined toxicity of free chlorine, chloramine and temperature to stage I larvae of the American lobster Homarus americanus

The differential effects of free chlorine and chloramine on stage I larvae of the American lobster Homarus americanus have been investigated in continuous flow bioassay units. Applied chloramine was more toxic than corresponding concentrations of applied free chlorine to lobster larvae with estimated lc₅₀ values at 25° of 16.30 mg/l applied free chlorine and 2.02 mg/l applied chloramine. The synergistic effect of temperature on the toxicity of both free chlorine and chloramine has also been demonstrated. Exposure to applied free chlorine at 20° resulted in no significant mortality of test organisms, whereas exposure at 30° resulted in an estimated lc₅₀ value of 2.50 mg/l. Applied chloramine was considerably more toxic with an estimated lc₅₀ value at 20° of 4.08 mg/l and at 30° of 0.56 mg/l.The action of each toxicant appeared to be an alteration of standard metabolic activity as revealed by changes in respiration rates during and after exposure to applied free chlorine and chloramine. Initial respiratory stress was detected during exposure to 0.05 mg/l applied chloramine and 5.00 mg/l applied free chlorine. Reductions in respiration rates 48 h after exposure were observed with exposure to all concentrations tested, similar results being obtained following exposure to 0.05 mg/l applied chloramine and 0.10 mg/l applied free chlorine. These results are indicative of the need for information in addition to that obtained in standard bioassays for an adequate assessment of chlorine toxicity.The apparent chlorine demand of the seawater used in this study was determined after removal of particulate and dissolved organics and ammonia. Approximately 18% of the applied level of free chlorine and chloramine was recovered as residuals, measured by amperometric titration; however, no reason for this low recovery has been determined. Until it has been established that undetected chlorine and chloramine in seawater do not result in the production of toxic compounds, both applied and residual levels should be reported in toxicity studies.