Biologically active secondary metabolites in white clover (Trifolium repens L.) – a review focusing on contents in the plant, plant–pest interactions and transformation

Summary.  To exploit biologically active compounds from white clover (Trifolium repens L.) for suppressing weeds and soil-borne diseases, either as isolated products (biopesticides) or through cultivars with enhanced production of these compounds, the biologically active compounds must be identified, plant content measured, and their fate in soil known. The present review summarizes the published knowledge needed for such exploitation; providing essential information on structure and concentration of flavonols, flavones, condensed tannins, isoflavones, isoflavanones, pterocarpans, coumestans, cyanogenic glucosides, and saponins in healthy and stressed white clover plants. Various stresses and particular cultivars affect the concentrations of several of the compounds. Information on biological effects and the degradation/transformation of these compounds in plants or by microorganisms is available. There is no information on the degradation pathway in soil, the mechanisms of exudation and leaching of compounds from plants, and soil sorption properties of the compounds. The clover soil fatigue problem is increasing in grasslands and causes problems especially in organic farming. Research efforts focused on biological elements of clover soil fatigue have not explained it, and the influence of secondary metabolites has not been investigated. There are few investigations into the interaction between beneficial fungi/fungal-diseases and the occurrence of biologically active secondary metabolites in white clover plants. Such studies are critical to better understand beneficial fungi and pathogens.     

Does iodine gas released from seaweed contribute to dietary iodine intake?

Thyroid hormone levels sufficient for brain development and normal metabolism require a minimal supply of iodine, mainly dietary. Living near the sea may confer advantages for iodine intake. Iodine (I₂) gas released from seaweeds may, through respiration, supply a significant fraction of daily iodine requirements. Gaseous iodine released over seaweed beds was measured by a new gas chromatography–mass spectrometry (GC–MS)-based method and iodine intake assessed by measuring urinary iodine (UI) excretion. Urine samples were obtained from female schoolchildren living in coastal seaweed rich and low seaweed abundance and inland areas of Ireland. Median I₂ ranged 154–905 pg/L (daytime downwind), with higher values (~1,287 pg/L) on still nights, 1,145–3,132 pg/L (over seaweed). A rough estimate of daily gaseous iodine intake in coastal areas, based upon an arbitrary respiration of 10,000L, ranged from 1 to 20 μg/day. Despite this relatively low potential I₂ intake, UI in populations living near a seaweed hotspot were much higher than in lower abundance seaweed coastal or inland areas (158, 71 and 58 μg/L, respectively). Higher values >150 μg/L were observed in 45.6% of (seaweed rich), 3.6% (lower seaweed), 2.3% (inland)) supporting the hypothesis that iodine intake in coastal regions may be dependent on seaweed abundance rather than proximity to the sea. The findings do not exclude the possibility of a significant role for iodine inhalation in influencing iodine status. Despite lacking iodized salt, coastal communities in seaweed-rich areas can maintain an adequate iodine supply. This observation brings new meaning to the expression “Sea air is good for you!”     

An investigation into the occurrence and distribution of polycyclic aromatic hydrocarbons in two soil size fractions at a former industrial site in NE England,UK using in situ PFE–GC–MS

Polycyclic aromatic hydrocarbon (PAH) concentrations were determined in 16 topsoils (0–10 cm) collected across the site of a former tar works in NE England. The soils were prepared in the laboratory to two different particle size fractions: <250 μm (fraction A) and >250 μm to <2 mm (fraction B). Sixteen priority PAHs were analysed in the soils using in situ pressurised fluid extraction (PFE) followed by gas chromatography—mass spectrometry (GC–MS). The average total PAH concentration in the soils ranged from 9.0 to 1,404 mg/kg (soil fraction A) and from 6.6 to 872 mg/kg (soil fraction B). These concentrations are high compared with other industrially contaminated soils reported in the international literature, indicating that the tar works warrants further investigation/remediation. A predominance of higher-molecular-weight compounds was determined in the samples, suggesting that the PAHs were of pyrogenic (anthropogenic) origin. Statistical comparison (t-test) of the mean total PAH concentrations in soil fractions A and B indicated that there was a significant difference (95% confidence interval) between the fractions in all but two of the soil samples. Additionally, comparisons of the distributions of individual PAHs (i.e. 16 PAHs × 16 soil samples) in soil fractions A and B demonstrated generally higher PAH concentrations in fraction A (i.e. 65.8% of all individual PAH concentrations were higher in soil fraction A). This is important because fraction A corresponds to the particle size thought to be most important in terms of human contact with soils and potential threats to human health.     

A novel soil bacterial strain degrading pyridines

Environmental pollution has become one of the most crucial problems of the modern society. Pyridine and its derivatives are one of the most widespread classes of heterocyclic industrial contaminants. Due to rather tough safe levels, thorough purification of the waste waters containing these ecotoxicants is required. However the existing chemical methods are not efficient. On the contrary, microbiological approach seems quite promising. A new strain degrading alkylpyridines was isolated from the soil contaminated with pyridine containing wastes. The strain was identified as Arthrobacter sp. KM-4 (VKM Ac-1098D). The strain completely consumes pyridine (2.5 g/l), 2-methylpyridine (2.5 g/l), 4-methylpyridine (1.5 g/l) and 2,6-dimethylpyridine (3 g/l) in aquatic solutions in 24 h. The intermediate products of the biodegradation process were identified using gas chromatography-mass spectrometry (GC–MS). Degradation schemes were proposed for pyridine and 2-methylpyridine. Previously unknown pathway of pyridines microbial degradation via intermediate formation of pyrrolidines was reliably proved by mass spectra and following synthesis of the identified compounds. New culture significantly surpasses all the known strains in the pyridines’ degrading efficiency. Arthrobacter sp. KM-4 is a promising culture for application for the purification of waste water.     

A pilot study on iodine in soils of Greater Kabul and Nangarhar provinces of Afghanistan

A robust and rapid methodology for the determination of iodine by inductively coupled plasma mass spectrometry in environmental samples is presented. Data were initially obtained for the validation of the analytical measurements, using 17 commercially available soil reference materials. The methodology was then tested on soil and water samples collected in Afghanistan where iodine deficiency and its effects are reportedly prevalent. Sample collections were conducted in Greater Kabul; the iodine in agricultural soils was determined to be in the range of 1.6–4.2 mg/kg and that in water drawn for drinking and irrigation was found to range from 9.9 to 22.7 μg/L. Samples were also collected in a second region, Nangarhar province, which is located to the east of Kabul, where goitres in the local population had been reported. The iodine content in soils and water at this location was 0.5–1.9 mg/kg and 5.4–9.4 μg/L, respectively. The organic content of soils in Kabul was found to be in the range of 1.9–4.2%; in Nangarhar, organic content ranged from 1.7 to 4.5%. All of the Afghan soils were slightly alkaline at pH 7.6–8.2.     

Chemical speciation and bioaccessibility of lead in surface soil and house dust,Lavrion urban area,Attiki, Hellas

In the Lavrion urban area study, Hellas, a five-step sequential extraction method was applied on samples of ‘soil’ (n = 224), affected by long-term mining and metallurgical activities, and house dust (n = 127), for the purpose of studying the potential bioaccessibility of lead and other metals to humans. In this paper, the Pb concentrations in soil and house dust samples are discussed, together with those in rocks and children’s blood. Lead is mainly associated with the carbonate, Fe–Mn oxides and residual fractions in soil and house dust. Considering the very low pH of gastric fluids (1–3), a high amount of metals, present in soil (810–152,000 mg/kg Pb) and house dust (418–18,600 mg/kg Pb), could be potentially bioaccessible. Consequently, children in the neighbourhoods with a large amount of metallurgical processing wastes have high blood-Pb concentrations (5.98–60.49 μg/100 ml; median 17.83 μg/100 ml; n = 235). It is concluded that the Lavrion urban and sub-urban environment is extremely hazardous to human health, and the Hellenic State authorities should urgently tackle this health-related hazard in order to improve the living conditions of local residents.     

Arsenic levels in rice grain and assessment of daily dietary intake of arsenic from rice in arsenic-contaminated regions of Bangladesh—implications to groundwater irrigation

Chronic exposure to arsenic (As) causes significant human health effects, including various cancers and skin disorders. Naturally elevated concentrations of As have been detected in the groundwater of Bangladesh. Dietary intake and drinking water are the major routes of As exposure for humans. The objectives of this study were to measure As concentrations in rice grain collected from households in As-affected villages of Bangladesh where groundwater is used for agricultural irrigation and to estimate the daily intake of As consumed by the villagers from rice. The median and mean total As contents in 214 rice grain samples were 131 and 143 μg/kg, respectively, with a range of 2–557 μg/kg (dry weight, dw). Arsenic concentrations in control rice samples imported from Pakistan and India and on sale in Australian supermarkets were significantly lower (p < 0.001) than in rice from contaminated areas. Daily dietary intake of As from rice was 56.4 μg for adults (males and females) while the total daily intake of As from rice and from drinking water was 888.4 and 706.4 μg for adult males and adult females, respectively. From our study, it appears that the villagers are consuming a significant amount of As from rice and drinking water. The results suggest that the communities in the villages studied are potentially at risk of suffering from arsenic-related diseases.     

Comparison of photoelectrochemical properties of TiO2-nanotube-array photoanode prepared by anodization in different electrolyte

Self-organized, well-crystallized and high aspect-ratio TiO₂ nanotube arrays (TNAs) have been prepared by anodic oxidation in dimethyl sulfoxide (DMSO) containing 5 wt% HF at 40 V (vs. Pt). A 50 h anodization results in a nanotube arrays approximately 19.4 μm in length, referred as long tube. As a comparison, the short titania nanotube arrays, about 500 nm in length, was obtained by anodization in HF aqueous solution, referred as short tube. Different characterization techniques (viz. FESEM, TEM, XRD and DRS) are used to study the nanotubular microstructure. The morphology of the nanotube electrodes shows an evident influence on their photocatalytic (PC) and photoelectrochemical reactivity. The long tube reveals enhanced photocurrent response and PC degradation efficiency of organic compounds. The kinetic constant of PC degradation of methylic orange (MO) for long tube electrode is found 1.55 times as high as the short tube. A significant photoelectrochemcial synergetic effect in MO degradation was observed on the long tube electrode and the photoelectrocatalytic (PEC) degradation of MO on long tube is 27% higher than its PC process.     

A 25-year record of polycyclic aromatic hydrocarbons in soils amended with sewage sludges

We studied polycyclic aromatic hydrocarbons (PAHs) in crop soils amended with 1000 tonnes dry weight of sewage sludges per 10,000 m² from 1974 to 1992, then after sludges addition from 1993 to 1999. The absence of variations of total PAHs levels of control soils, averaging at 123 μg/Kg, shows the absence of horizontal contamination. During sludges addition, the total PAHs levels in amended soils increased from 232 to 402 μg/Kg. Seven years after sludges addition, it decreased to 275 μg/Kg, which is still more than twice –the levels of control soils. This finding shows that sludges PAHs are preserved in crop soils for long periods of time, on a human scale.     

Growth, carbon, nitrogen and caloric content of Solea senegalensis (Pisces: Soleidae) from egg fertilization to metamorphosis

Eggs and larvae of the Senegal sole, Solea senegalensis Kaup, were reared from fertilization until the end of metamorphosis, which occurs by Day 17 after hatching at 19.5 °C. Changes in energy content and biomass quality were studied in terms of dry weight and of carbon, nitrogen and energy content. S. senegalensis spawned eggs of about 1 mm diameter which hatched 38 h after fertilization. Average dry weight of individual eggs was 46 μg, the chorion accounting for about 18% of total dry weight. Gross energy of recently fertilized sole eggs was approximately 1 J egg⁻¹. From fertilization to hatching, eggs lost 8% of their total energy (chorion not included). After hatching, larvae lost 14% of their initial energy until the start of feeding which occurred about 48 h afterwards. The principal components catabolized during embryogenesis were carbon-rich compounds that decreased by 26%, while nitrogen-rich compounds decreased by only 10% and were practically unaltered from hatching to the start of feeding. Feeding larvae displayed constant growth during the period studied (specific growth rate on a dry weight basis was 0.26 d⁻¹). The relative proportion of carbon and nitrogen content revealed an accumulation of high energy compounds in the days before metamorphosis. By Day 14, the energy content reached values similar to those of recently hatched embryos, but decreased again during metamorphosis. Received: 10 June 1998 / Accepted: 28 January 1999     

HCH residues in point-source contaminated samples of the Teltow Canal in Berlin,Germany

Contaminated groundwater and a riverine sediment core heavily affected by the same industrial point source were analysed for hexachlorocyclohexanes (HCH) and its degradation products. A detailed quantification by GC/MS revealed contamination levels up to 730 μg/L and 396 ng/g in sum for the water and sediment samples, respectively. The isomer pattern differed significantly in both compartments. The ground water samples were depleted in γ-HCH, whereas a significant loss of α-HCH was evident in the sediments as compared to the technical composition. The data obtained revealed interesting insights into the transformation behaviour and fate of HCH mixtures in anaerobic environmental compartments. In the affected groundwater system an ongoing microbial degradation was pointed out by the identification of indicative anaerobic metabolites. On the contrary in the sedimentary system a high environmental stability or rather a hindered degradation was observed as indicated by unaltered concentration levels as compared to production rates as well as by the absence of metabolites. Interestingly, the environmental fate of HCH in subaquatic sediments as well as in anaerobic ground water differs highly in contrast to the behaviour in anaerobic soil or surface water systems. Further on, it has to be stated, that the knowledge about the long-term behaviour of HCH residues in sedimentary material under anaerobic conditions is rather limited so far.     

Tracing the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain,India: a source identification perspective

Arsenic contamination in groundwater is of increasing concern because of its high toxicity and widespread occurrence. This study is an effort to trace the factors responsible for arsenic enrichment in groundwater of the middle Gangetic Plain of India through major ion chemistry, arsenic speciation, sediment grain-size analyses, and multivariate statistical techniques. The study focuses on the distinction between the contributions of natural weathering and anthropogenic inputs of arsenic with its spatial distribution and seasonal variations in the plain of the state Bihar of India. Thirty-six groundwater and one sediment core samples were collected in the pre-monsoon and post-monsoon seasons. Various graphical plots and statistical analysis were carried out using chemical data to enable hydrochemical evaluation of the aquifer system based on the ionic constituents, water types, hydrochemical facies, and factors controlling groundwater quality. Results suggest that the groundwater is characterized by slightly alkaline pH with moderate to strong reducing nature. The general trend of various ions was found to be Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ > NH₄ ⁺; and HCO₃ ⁻ > Cl⁻ > SO₄ ²⁻ > NO₃ ⁻ > PO₄ ³⁻ > F⁻ in both seasons. Spatial and temporal variations showed a slightly higher arsenic concentration in the pre-monsoon period (118 μg/L) than in the post-monsoon period (114 μg/L). Results of correlation analyses indicate that arsenic contamination is strongly associated with high concentrations of Fe, PO₄ ³⁻, and NH₄ ⁺ but relatively low Mn concentrations. Further, the enrichment of arsenic is more prevalent in the proximity of the Ganges River, indicating that fluvial input is the main source of arsenic. Grain size analyses of sediment core samples revealed clay (fine-grained) strata between 4.5 and 7.5 m deep that govern the vertical distribution of arsenic. The weathering of carbonate and silicate minerals along with surface-groundwater interactions, ion exchange, and anthropogenic activities seem to be the processes governing groundwater contamination, including with arsenic. Although the percentage of wells exceeding the permissible limit (50 μg/L) was less (47%) than that reported in Bangladesh and West Bengal, the percentage contribution of toxic As(III) to total arsenic concentration is quite high (66%). This study is vital considering that groundwater is the exclusive source of drinking water in the region and not only makes situation alarming but also calls for immediate attention.     

Biotransformation of 4-nerolidylcatechol by Heraclides brasiliensis (Lepidoptera: Papilionidae) reduces the toxicity of Piper umbellata (Piperaceae)

Heraclides brasiliensis (Lepidoptera: Papilionidae) larvae feed preferably on Piperaceae, foraging successfully on leaf tissues even though species of this contain high levels of secondary metabolites such as amides and lignans, associated with diverse biological activities including insecticidal properties. Studies examining the metabolism of chemical constituents in Piperaceae by insects are rare. In this study, we characterized the metabolites of 4-nerolidylcatechol (4-NC), the major constituent of Piper umbellata (Piperaceae), and E-2,3-dihydro-3-(3,4-dihydroxyphenyl)farnesoic acid, compounds from fecal material of H. brasiliensis larvae fed a diet containing only P. umbellata leaves. The biotransformed product was also detected in larval and pupal tissues. Moreover, we observed deactivation of the toxicity of P. umbellata leaves against brine shrimp after their metabolism in H. brasiliensis larvae from a LC₅₀ of 523.3 to 3,460.7 μg/mL. This deactivation is closely associated with the biotransformation of 4-NC to E-2,3-dihydro-3-(3,4-dihydroxyphenyl)farnesoic acid, which showed LC₅₀ of 8.0 and >1,000 μg/mL, respectively.     

Effect of acclimatization to low temperature and reduced light on the response of reef corals to elevated temperature

This study tested the effects of acclimatization on the response of corals to elevated temperature, using juvenile massive Porites spp. and branching P. irregularis from Moorea (W149°50′, S17°30′). During April and May 2006, corals were acclimatized for 15 days to cool (25.7°C) or ambient (27.7°C) temperature, under shaded (352 μmol photons m⁻² s⁻¹) or ambient (554 μmol photons m⁻² s⁻¹) natural light, and then incubated for 7 days at ambient or high temperature (31.1°C), under ambient light (659 μmol photons m⁻² s⁻¹). The response to acclimatization was assessed as biomass, maximum dark-adapted quantum yield of PSII (F _v/F _m), and growth, and the effect of the subsequent treatment was assessed as F _v/F _m and growth. Relative to the controls (i.e., ambient temperature/ambient light), massive Porites spp. responded to acclimatization through increases in biomass under ambient temperature/shade, and low temperature/ambient light, whereas P. irregularis responded through reduced growth under ambient temperature/shade, and low temperature/ambient light. Acclimatization affected the response to thermal stress for massive Porites spp. (but not P. irregularis), with an interaction between the acclimatization and subsequent treatments for growth. This interaction resulted from a lessening of the negative effects of high temperature after acclimatizing to ambient temperature/shade, but an accentuation of the effect after acclimatizing to low temperature/shade. It is possible that changes in biomass for massive Porites spp. are important in modulating the response to high temperature, with the taxonomic variation in this effect potentially resulting from differences in morphology. These results demonstrate that corals can acclimatize during short exposures to downward excursions in temperature and light, which subsequently affects their response to thermal stress. Moreover, even con-generic taxa differ in this capacity, which could affect coral community structure. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

13C-dating, the first method to calculate the relative age of molecular substance homologues in soil

This article reports the design of ¹³C-dating, the first method to calculate the relative age of molecular substance homologues occurring in fractions from the same soil sample. Soil is a major carbon pool impacting modern climate by CO₂ release and uptake. Molecular substances that sequester carbon in soils are poorly known due to the absence of methods to study molecular-level C dynamics over agricultural time scales, e.g., 0–200 years. Here, I design a method to calculate the relative age of the plant-derived C₃₁ n-alkane occurring in 6 fractions from a soil sample naturally ¹³C-labelled by maize cropping during 23 years. Soil fractions are the bulk soil extract, two humin-encapsulated fractions and three particle-size fractions. Results show that C₃₁ n-alkane homologues have relative ages ranging from −6.7 years for the humin-encapsulated homologue to +25.1 years for the 200–2,000-μm fraction homologue. Such a wide variation of 31.8 years evidences temporal pools of molecular substances in soil. This finding also reveals that physical encapsulation can strikingly change the dynamics of a single molecular substance. ¹³C-dating thus allows to assess the carbon storage potential of molecular substances from crop soils. Such knowledge will help to identify molecular compounds, associated soil pools and agricultural practices that favour carbon sequestration. ¹³C-dating is further applicable to any environmental sample containing organic matter subjected to a ¹³C isotope shift with time. ¹³C-dating will also help to study the sequestration and delayed release of chemicals in various disciplines, such as pollutants in environmental sciences, pharmaceuticals in medicine, and nutrients in food science.     

Diurnal cycle and kinetics of ammonium assimilation in the green alga <Emphasis Type="Italic">Ulva pertusa</Emphasis>

The kinetics of ammonium assimilation was investigated in Ulva pertusa (Chlorophyceae, Ulvales) from northeastern New Zealand. Ammonium assimilation exhibited Michaelis–Menten kinetics with a maximum rate of assimilation (V _max) of 54 ± 5 μmol g⁻¹ dry weight h⁻¹ and half-saturation constant (K _m) of 23 ± 8 μM. In contrast, values for ammonium uptake were considerably higher with a V _max of 316 ± 59 μmol g⁻¹ dry weight h⁻¹ and K _m of 135 ± 46 μM. At environmentally relevant ammonium concentrations (5 μM), assimilation accounted for most (70%) of the ammonium taken up. Darkness decreased the maximum rate of ammonium assimilation by 83%. We investigated the hypothesis that rates of biosynthetic processes are greater in the early part of the day in Ulva. Consistent with this hypothesis, the maximum rate of ammonium assimilation in U. pertusa peaked in the morning and coincided with low levels of the photosynthetic product sucrose, which peaked in the afternoon. There was a diurnal cycle in the rate of ammonium uptake and assimilation in light and dark, but the amplitude was much greater for assimilation than uptake. Moreover, our data suggest that net ammonium assimilation only occurs during the day in U. pertusa. We suggest that two major roles for diurnal cycles are minimisation of interspecific competition for resources and metabolic costs.     

Effect of body mass,temperature and food deprivation on oxygen consumption rate of common cuttlefish <Emphasis Type="Italic">Sepia officinalis</Emphasis>

Predictions of short and long term changes in Sepia officinalis metabolism are useful, since this species is both economically important for aquaculture and also is an ideal experimental laboratory organism. In this study standard and routine oxygen consumption rates of newly hatched and juvenile laboratory raised cuttlefish S. officinalis ranging between 0.04 and 18.48 g dry body mass (Dm), were measured over a range of temperatures (10, 15, 20 and 25°C). The mass exponent (b) ranged between 0.706 and 0.992 for standard oxygen consumption and between 0.694 and 0.990 for routine oxygen consumption. Oxygen consumption scaled allometrically (b = 0.7) with body mass for cuttlefish <2 g Dm and isometrically (b = 1) thereafter. No significant differences were apparent amongst the slopes of oxygen consumption and body mass at different temperatures for standard and routine oxygen consumption. However, the intercepts differed significantly amongst the regression lines, indicating a significant effect of temperature on the magnitude of oxygen consumption. The combined effect of temperature (T) and dry body mass (Dm) are best described by the following equations: cuttlefish <2 g, MO₂ = 0.116Dm^0.7111.086 ^T and >2 g, MO₂ = 0.076Dm^0.9831.091 ^T for standard oxygen consumption; cuttlefish <2 g, MO₂ = 0.538Dm^0.7291.057 ^T and >2 g, MO₂ = 0.225Dm^0.9621.081 ^T for routine oxygen consumption. Using these equations it was estimated that a cuttlefish of 1 g Dm held at 20°C, eating 5% Dm day⁻¹ and undergoing standard and routine metabolism consumes 21.3 and 35.4%, respectively of its total daily energy intake. Juvenile cuttlefish (3.32–5.08 g Dm) held at 15°C and deprived of food for 27 days maintained a stable standard oxygen consumption rate for the first 6 days following starvation. By the 18th day without food, oxygen consumption rate had declined by 53% and further declined to 65% below the standard oxygen consumption rate on the 27th day. Upon resumption of feeding, the respiration rate returned immediately to the initial level prior to food deprivation. The present study defines the basic energy requirements and general physiological state of young cuttlefish at temperatures of 10–25°C with and without food.     

A comparative study on arsenic and humic substances in alluvial aquifers of Bengal delta plain (NW Bangladesh), Chianan plain (SW Taiwan) and Lanyang plain (NE Taiwan): implication of arsenic mobilization mechanisms

Humic substances in groundwater and aquifer sediments from the arsenicosis and Blackfoot disease (BFD) affected areas in Bangladesh (Bengal delta plain) and Taiwan (Lanyang plain and Chianan plain) were characterized using fluorescence spectrophotometry and Fourier transform infrared (FT-IR) spectroscopy. The results demonstrate that the mean concentration of As and relative intensity of fluorescent humic substances are higher in the Chianan plain groundwater than those in the Lanyang plain and Bengal delta plain groundwater. The mean As concentrations in Bengal delta plain, Chianan plain, and Lanyang plain are 50.65 μg/l (2.8–170.8 μg/l, n = 20), 393 μg/l (9–704 μg/l, n = 5), and 104.5 μg/l (2.51–543 μg/l, n = 6), respectively. Average concentrations and relative fluorescent intensity of humic substances in groundwater are 25.381 QSU (quinine standard unit) and 17.78 in the Bengal delta plain, 184.032 QSU and 128.41 in the Chianan plain, and 77.56 QSU and 53.43 in the Lanyang plain. Moreover, FT-IR analysis shows that the humic substances extracted from the Chianan plain groundwater contain phenolic, alkanes, aromatic ring and amine groups, which tend to form metal carbon bonds with As and other trace elements. By contrast, the spectra show that humic substances are largely absent from sediments and groundwater in the Bengal delta plain and Lanyang plain. The data suggest that the reductive dissolution of As-adsorbed Mn oxyhydroxides is the most probable mechanism for mobilization of As in the Bengal delta plain. However, in the Chianan plain and Lanyang plain, microbially mediated reductive dissolution of As-adsorbed amorphous/crystalline Fe oxyhydroxides in organic-rich sediments is the primary mechanism for releasing As to groundwater. High levels of As and humic substances possibly play a critical role in causing the unique BFD in the Chianan plain of SW Taiwan.     

The influence of iron stores on cadmium body burden in a Thai population

Cadmium is a toxin of increasing public health concern due to its presence in most human foodstuffs and in cigarette smoke. Exposure to cadmium leads to tissue bioaccumulation and, in particular, has nephrotoxic effects. The aim of the present study was to investigate the association between cadmium body burden and iron stores in a Thai population. A total of 182 healthy adult Thai subjects of both genders (89 males, 93 females) aged between 18 and 57 years and weighing 40–95 kg were included in this study. The total amounts of cadmium excreted in urine over 2 h (μg/g creatinine) were used as an index of long-term cadmium exposure. Quantitation of cadmium was performed using electrothermal (graphite furnace) atomic absorption spectrometry. The urinary cadmium excreted displayed a normal frequency distribution. The average urinary cadmium level did not exceed the WHO maximum tolerable internal dose for the non-exposed population (2 μg/g creatinine). Body iron stores reflected by serum ferritin levels did not show any correlation with cadmium burden in both males and females, although a relatively stronger influence of body iron store status on cadmium burden was shown in females. When the levels of serum ferritin were stratified into five levels (<20, 20–100, 101–200, 201–300, and >300 μg/l), a significant difference in total cadmium body burden was observed between females and males only in the group with a low level of serum ferritin of <20 μg/l. The cadmium body burden in females was about twice that in males in this group.     

Human hair mercury levels in the Wanshan mercury mining area,Guizhou Province,China

The total mercury (T-Hg) and methyl mercury (Me-Hg) concentrations in the hair were measured to evaluate mercury (Hg) exposure for the residents in Da-shui-xi Village (DSX) and Xia-chang-xi Village (XCX) in the Wanshan Hg mining area, Guizhou Province, Southwestern China. The mean concentrations in the hair of DSX residents were 5.5 ± 2.7 μg/g and 1.9 ± 0.9 μg/g for T-Hg and Me-Hg, respectively. The concentrations in the hair of XCX residents were 3.3 ± 1.4 μg/g and 1.2 ± 0.5 μg/g for T-Hg and Me-Hg, respectively. Hair Me-Hg concentrations were significantly correlated to T-Hg (r = 0.42, P < 0.01) in the two sites; on average, hair Me-Hg concentration accounted for 40 and 44% of T-Hg for DSX and XCX residents, respectively. Age has no obvious correlation with hair Hg and the hair Hg levels showed a significant gender difference, with higher T-Hg and Me-Hg concentrations in the hair from males than females. The rice collected from the two sites showed high levels of T-Hg and Me-Hg concentration. The results indicated a certain Hg exposure for the residents in DSX and XCX in the Wanshan Hg mining area.