A sensitive spectrophotometric method for the determination of arsenic in environmental samples

We developed a cost-effective and sensitive spectrophotometric method for the determination of arsenic at trace level using a new reagent, leuco malachite green. Here we show that, arsenic reacts with potassium iodate in acidic conditions to liberate iodine, and the liberated iodine selectively oxidizes leuco malachite green to malachite green dye. We studied the Beer’s law at 617 nm, which showed linearity over the concentration range 0.09–0.9 μg ml⁻¹ of arsenic. We show that the molar absorptivity, Sandell’s sensitivity and detection limit of the method are 6.1 × 10⁴ l mol⁻¹ cm⁻¹, 0.0012 μg cm⁻² and 0.025 μg ml⁻¹, respectively. We applied the developed method for the determination of arsenic in environmental samples.     

Automated method for the determination of total arsenic and selenium in natural and drinking water by HG-AAS

A multicommutated flow system was designed and evaluated for the determination of total arsenic and selenium by Hydride Generation Atomic Absorption Spectrometry (HG-AAS). It was applied to the determination of arsenic and selenium in samples of natural and drinking water. Detection limits were 0.46 and 0.08 μg l⁻¹ for arsenic and selenium, respectively; sampling frequency was 120 samples h⁻¹ for arsenic and 160 samples h⁻¹ for selenium. Linear ranges found were 1.54–10 μg l⁻¹ (R = 0.999) for arsenic and 0.27–27 μg l⁻¹ (R = 0.999) for selenium. Accuracy was evaluated by spiking various water samples and using a reference material. Recoveries were in the range 95–116%. Analytical precision (s _r (%), n = 10) was 6% for both elements. Compared with the Standard Methods, APHA, 3114B manual method, the system consumes at least 10 times less sample per determination, and the quantities of acid and reducing agent used are significantly lower with a reduction in the generation of pollutants and waste. As an additional advantage, the system is very fast, efficient and environmentally friendly for monitoring total arsenic and selenium levels in waters.     

The determination of fluoride in water in the presence of organic acids and iron using a fluoride-selective electrode

Surface waters in Scotland, notably from upland catchment areas, are commonly enriched in iron and organic acids. This study investigated the impact of these species on the direct potentiometric determination of fluoride using a fluoride-selective electrode. As the electrode technique is commonly used to monitor the fluoride content of potable waters, it is important that these effects are evaluated if such waters are to be fluoridated. The determination method used was that defined by Nicholson (1983) and Nicholson and Duff (1981) to minimise errors. This employs the TISAB III-TAC buffer system with the following composition (in 1L): 58.0 g sodium chloride, 57.0 mL glacial acetic acid, 4.0 g CDTA, 243.0 g tri-ammonium citrate adjusted to pH 5.4 with 10 M sodium hydroxide. Experimental solutions of fluoride with organic acid or iron were prepared, and the effect on fluoride concentration determined for each combination. Concentrations used: fluoride: 0.1, 1.0 mg L⁻¹; humic acid: 5, 10, 100, 1000, 10,000 mg L⁻¹; oxalic acid: 5, 10, 100, 1000, 10,000 mg L⁻¹; iron(III): 1, 10, 100, 500 mg L⁻¹; Humic acid (HA) concentrations had no impact on the determination of fluoride at the 1.0 mg L⁻¹ level. However, with 0.1 mg L⁻¹; F⁻, an increase in the apparent fluoride concentration was observed when HA > 1,000 mg L⁻¹; this increased with increasing HA content to a maximum of ∼600%. Oxalic acid (OA) generally had no impact on the fluoride determinations at the 1.0 mg L⁻¹; level, but at an OA concentration of 10,000 mg L⁻¹; fluoride concentrations were reduced by ∼50%. At 0.1 mg L⁻¹ F⁻, increasing OA concentrations produce a steady increase in the fluoride concentration of up to 200% with 1,000 mg L⁻¹; OA, greater OA contents produce a fall in the fluoride content. Iron had no effect on the fluoride determinations at both the 0.1 and 1.0 mg L⁻¹ levels. The causes of the apparent increases in fluoride concentration have not been determined, although fluoride contamination by the reagents has been ruled-out. However, the results demonstrate that the defined method and buffer system is suitable for the determination of fluoride in the presence of iron and organic acids at naturally occurring levels, and that fluoride will not be masked from detection.     

Arsenic contamination in water,soil, sediment and rice of central India

Arsenic contamination in the environment (i.e. surface, well and tube-well water, soil, sediment and rice samples) of central India (i.e. Ambagarh Chauki, Chhattisgarh) is reported. The concentration of the total arsenic in the samples i.e. water (n=64), soil (n=30), sediment (n=27) and rice grain (n=10) were ranged from 15 to 825 μg L⁻¹, 9 to 390 mg kg⁻¹, 19 to 489 mg kg⁻¹ and 0.018 to 0.446 mg kg⁻¹, respectively. In all type of waters, the arsenic levels exceeded the permissible limit, 10 μg L⁻¹. The most toxic and mobile inorganic species i.e. As(III) and As(V) are predominantly present in water of this region. The soils have relatively higher contents of arsenic and other elements i.e. Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Ga, Zr, Sn, Sb, Pb and U. The mean arsenic contents in soil of this region are much higher than in arsenic soil of West Bengal and Bangladesh. The lowest level of arsenic in the soil of this region is 3.7 mg kg⁻¹ with median value of 9.5 mg kg⁻¹. The arsenic contents in the sediments are at least 2-folds higher than in the soil. The sources of arsenic contamination in the soil of this region are expected from the rock weathering as well as the atmospheric deposition. The environmental samples i.e. water, soil dust, food, etc. are expected the major exposure for the arsenic contamination. The most of people living in this region are suffering with arsenic borne diseases (i.e. melanosis, keratosis, skin cancer, etc.).     

Growth and development rates of Calanus finmarchicus nauplii during a diatom spring bloom

Growth and development rates were determined for nauplii of Calanus finmarchicus (Gunnerus) in the near-shore waters of a western Norwegian fjord from in situ mesocosm incubations. The major food source for the nauplii was diatoms, but Phaeocystis sp., dinoflagellates and ciliates were also part of the diet. At local temperatures ranging from 4.8 to 5.2 °C the cumulative median development time from hatching to Nauplius VI was 19 d. The time taken to molt to the next naupliar stage was approximately constant (3 d) from Stages IV to VI, but Stage III needed the longest development time (5 d). The instantaneous growth rate in terms of body carbon was negative from hatching to Nauplius Stage II, but as high as 0.25 to 0.30 d⁻¹ from Stage III to V. Enhancement of food resources by nutrient addition led to no significant change in specific growth rates. Additionally, the cohorts from different nutrient regimes showed almost equal development time, size and body carbon within stages. Length–weight relationships of nauplii from the two different food resources were: W _{low resources} = 4.17 × 10⁻⁶ × L ^2.03 (r ² = 0.84) and W _{high resources} = 4.29 × 10⁻⁶ × L ^2.05 (r ² = 0.92), where weight (W) is in micrograms of C and body length (L) in micrometers. The natural body morphology of naupliar stages I to VI is illustrated with digital images, including the final molt from Nauplius VI to Copepodid Stage I. In general, development of the nauplii was faster than that of the copepodids of C. finmarchicus, and structural growth was exponential from naupliar stages III to VI. This study validates our earlier results that nauplii of C. finmarchicus can obtain high growth and nearly maximal developmental rates at relatively low food levels (∼50 μg C l⁻¹), suggesting that nauplii exhibit far less dependence on food supply than copepodids. Received: 30 July 1999 / Accepted: 7 March 2000     

Inhibition of Na+/K+-ATPase and of active ion-transport functions in the gills of the shore crab Carcinus maenas induced by cadmium

Inhibition of Na⁺/K⁺-ATPase from gill plasma membranes of the shore crab Carcinus maenas by cadmium was investigated and compared with inhibitory effects by known antagonists (ouabain and Ca²⁺). For comparative considerations the Cd²⁺-inhibition of the enzyme from dog kidney was also tested. Na⁺/K⁺-ATPase from dog kidney and from crab gill differed greatly in sensitivity against ouabain. The inhibition constant K _i of the dog enzyme amounted to 9.1 × 10⁻⁷ mol l⁻¹, i.e. more than 300-fold smaller than the K _i of 2.9 × 10⁻⁴ mol l⁻¹ determined for the crab enzyme. Ca²⁺ inhibited the activity of Na⁺/K⁺-ATPase from crab gill plasma membranes with a K _i of 4.3 × 10⁻⁴ mol l⁻¹. The Na⁺/K⁺-ATPase from crab gill was inhibited by Cd²⁺ with a K _i of 9.1 × 10⁻⁵ mol l⁻¹. Cd²⁺ inhibited the Na⁺/K⁺-ATPase from dog kidney with a K _i (6.4 × 10⁻⁵ mol l⁻¹) comparable to that observed in the crab gill enzyme. Under experimental conditions Cd²⁺-inhibition of Na⁺/K⁺-ATPase was irreversible. Repeated washing, centrifugation and homogenization of the plasma membranes (four times) with Cd²⁺-free buffer did not restore any activity lost in the presence of 1 × 10⁻³ mol l⁻¹ Cd²⁺. Since ouabain-insensitive (nonspecific) ATPases in the plasma membrane fraction of crab gills were inhibited by Cd²⁺ in the same way as Na⁺/K⁺-ATPase, the heavy metal is considered as an unspecific ATPase inhibitor. Comparing these results with literature data on Cd²⁺-binding to electrophoretically separated proteins suggests that Na⁺/K⁺-ATPase is a Cd²⁺-binding enzyme. The results obtained on Na⁺/K⁺-ATPase were reflected by Cd²⁺-inhibition of the branchial ion-transport functions depending on this enzyme. The transepithelial short-circuit current of isolated gill half lamellae, a direct measure of area-specific active ion uptake, and the transepithelial potential difference of isolated, perfused whole gills, also indicative of active ion uptake, were inhibited by the heavy metal in a time- and dose-dependent mode. Remarkably these inhibitions were also irreversible. These findings are ecologically and biomedically significant: even when the actual environmental or tissue concentrations measured are low, biological microstructures such as Na⁺/K⁺-ATPase may accumulate the heavy metal by tight binding over prolonged periods until the first inhibitory effects occur. Received: 25 June 1997 / Accepted: 25 August 1997     

Concentrations of inorganic elements in 20 municipal waters in Sweden before and after treatment – links to human health

The water chemistry of 20 municipal water treatment plants in southern Sweden, representing various bedrock situations, and water qualities, were investigated. Four water samples, raw and treated, were collected from each plant and analyzed by predominantly ICP-OES and ICP-MS at four occasions from June to December, 2001. The concentrations of Ca, Mg, K, Na, HCO₃ and a number of micronutrients, varied considerably in treated waters from the studied plants (ranges; Ca: 9.1–53.7 mg L⁻¹, Mg: 1.4–10.9 mg L⁻¹, K: 1.1–4.8 mg L⁻¹, Na; 5.4–75.6 mg L⁻¹, HCO₃: 27–217 mg L⁻¹). The elimination of Fe and Mn from raw water was efficient in all treatments investigated, giving concentrations in treated waters below the detection limits at some plants. Softening filters gave waters with Ca-concentrations comparable to the softest waters in this study. Adjustment of pH by use of chemicals like lye, soda or lime, modified the consumer water composition significantly, besides raising the pH. It was estimated that drinking water contributed to approximately 2.2–13% of the daily Ca uptake, if the gastrointestinal uptake efficiency from food and water was estimated to be around 50%. The corresponding figures for Mg was 1.0–7% and for F 0–59%. None of the studied elements showed any significant time trends in raw or treated waters during the follow-up period. The concentrations of potentially toxic metals such as Al, Pb and U were low and did not indicate risks for adverse health effects (ranges; Al: 0.5–2.3 μg L⁻¹, Pb: 0–0.3 μg L⁻¹, U: 0.2.5 μg L⁻¹).     

Mobilization of arsenic and other trace elements of health concern in groundwater from the Salí River Basin, Tucumán Province, Argentina

The Salí River Basin in north-west Argentina (7,000 km²) is composed of a sequence of Tertiary and Quaternary loess deposits, which have been substantially reworked by fluvial and aeolian processes. As with other areas of the Chaco-Pampean Plain, groundwater in the basin suffers a range of chemical quality problems, including arsenic (concentrations in the range of 12.2–1,660 μg L⁻¹), fluoride (50–8,740 μg L⁻¹), boron (34.0–9,550 μg L⁻¹), vanadium (30.7–300 μg L⁻¹) and uranium (0.03–125 μg L⁻¹). Shallow groundwater (depths up to 15 m) has particularly high concentrations of these elements. Exceedances above WHO (2011) guideline values are 100% for As, 35% for B, 21% for U and 17% for F. Concentrations in deep (>200 m) and artesian groundwater in the basin are also often high, though less extreme than at shallow depths. The waters are oxidizing, with often high bicarbonate concentrations (50.0–1,260 mg L⁻¹) and pH (6.28–9.24). The ultimate sources of these trace elements are the volcanic components of the loess deposits, although sorption reactions involving secondary Al and Fe oxides also regulate the distribution and mobility of trace elements in the aquifers. In addition, concentrations of chromium lie in range of 79.4–232 μg L⁻¹ in shallow groundwater, 129–250 μg L⁻¹ in deep groundwater and 110–218 μg L⁻¹ in artesian groundwater. All exceed the WHO guideline value of 50 μg L⁻¹. Their origin is likely to be predominantly geogenic, present as chromate in the ambient oxic and alkaline aquifer conditions.     

Arsenic in groundwaters of the Lower Mekong

Increasing incidence and awareness of arsenic in many alluvial aquifers of South-east Asia has raised concern over possible arsenic in the Lower Mekong Basin. Here, we have undertaken new research and reviewed many previous small-scale studies to provide a comprehensive overview of the status of arsenic in aquifers of Cambodia and the Cuu Long Delta of Vietnam. In general natural arsenic originates from the Upper Mekong basin, rather than from the local geology, and is widespread in soils at typical concentrations of between 8 and 16 ppm; (dry weight). Industrial and agricultural arsenic is localised and relatively unimportant compared to the natural alluvial arsenic. Aquifers most typically contain groundwaters of no more than 10 μg L⁻¹, although scattered anomalous areas of 10 to 30 μg L⁻¹ are also quite common. The most serious, but possibly ephemeral arsenic anomalies, of up to 600 μg L⁻¹, are associated with iron and organic-rich flood-plain sediments subject to very large flood-related fluctuations in water level, resulting in transient arsenopyrite dissolution under oxidizing conditions. In general, however, high-arsenic groundwaters result from the competing interaction between sorption and dissolution processes, in which arsenic is only released under reducing and slightly alkaline conditions. High arsenic groundwaters are found both in shallow water-tables, and in deeper aquifers of between 100 and 120 m depth. There is no evidence of widespread arsenicosis, but there are serious localised health-hazards, and some risk of low-level arsenic ingestion through indirect pathways, such as through contaminated rice and aquaculture. An almost ubiquitous presence of arsenic in soils, together with the likelihood of greatly increased groundwater extraction in the future, will require continuing caution in water resources development throughout the region.     

Environmental geochemistry study of arsenic in Western Hunan mining area,P.R. China

The geochemical characteristics of arsenic in the soil of the Western Hunan mining area of P.R. China were systematically studied. The results show that the strata of Western Hunan are rich in arsenic and that Western Hunan is a geochemically abnormal region for arsenic. The experimental study on speciation in the strata also indicates that the speciation of arsenic in the Neoproterozoic-Cambrian strata are mainly easily transferred speciation (exchangeable, carbonate-bound, sulfides-bound), which are approaching or exceed 60%. Arsenic content in the main soil of Western Hunan is in the range of 8.8–22.8 μg g⁻¹, the mean value is 16.1 μg g⁻¹, which is larger than the arsenic background value of Hunan soil. The distribution of rock with high arsenic content or high easily transferred arsenic speciation is consistent with the distribution of high arsenic content soil. In the mining region, part soils and river/brook waters were polluted by mine tailings and mining/smelting waste water. The arsenic content in polluted paddy soils and river/brook water is 46.26–496.19 μg g⁻¹, 0.3–16.5 mgL⁻¹, respectively. The positive abnormality and pollution of arsenic in the soil and water affects the arsenic content of the crop and the inhabitants’ health.     

Strong variability in bacterioplankton abundance and production in central and western Bay of Bengal

With large influx of freshwater that decreases sea-surface salinities, weak wind forcing of <10 m s⁻¹ and almost always warm (>28°C) sea-surface temperature that stratifies and shallows the mixed layer leading to low or no nutrient injections into the surface, primary production in Bay of Bengal is reportedly low. As a consequence, the Bay of Bengal is considered as a region of low biological productivity. Along with many biological parameters, bacterioplankton abundance and production were measured in the Bay of Bengal during post monsoon (September–October 2002) along an open ocean transect, in the central Bay (CB, 88°E) and the other transect in the western Bay (WB). The latter representing the coastal influenced shelf/slope waters. Bacterioplankton abundances (<2 × 10⁹cells l⁻¹) were similar to those reported from the HNLC equatorial Pacific and the highly productive northern Arabian Sea. Yet, the thymidine uptake rates along CB (average of 1.46 pM h⁻¹) and WB (average of 1.40 pM h⁻¹) were less than those from the northwestern Indian Ocean. These abundances and uptake rates were higher than those in the oligotrophic northwestern Sargasso Sea (<7 × 10⁸ cells l⁻¹; av 1.0 pM h⁻¹). Concentrations of chlorophyll a (chl a), primary production rates and total organic carbon (TOC) were also measured for a comparison of heterotrophic and autotrophic production. In the WB, bacterioplankton carbon biomass equaled ∼ 95% of chl a carbon than just 31% in the CB. Average bacterial:primary production (BP:PP) ratios accounted for 29% in the CB and 31% in the WB. This is mainly due to lower primary productivity (PP) in the WB (281 mg C m⁻² d⁻¹) than in the CB (306 mg C m⁻² day⁻¹). This study indicates that bacteria–phytoplankton relationship differs in the open (CB) and coastal waters (WB). Higher abundance and contrastingly low bacterial production (BP) in WB may be because of the riverine bacteria, brought in through discharges, becoming dormant and unable to reproduce in salinities of 28 or more psu. Heterotrophic bacteria appear to utilize in situ DOC rather rapidly and their carbon demand is ∼50% of daily primary production. It is also apparent that allochthonous organic matter, in particular in the western Bay, is important for meeting their carbon demand.     

Kinetic measurements of metal accumulation in two marine macroalgae

 We measured the uptake kinetics of four metals (Cd, Cr, Se and Zn) in two marine macroalgae (the green alga Ulva lactuca and the red alga Gracilaria blodgettii). Metal uptake generally displayed a linear pattern with increasing exposure time. With the exception of Cr, which exhibited comparable uptake rate constants at different concentrations, uptake rate constants of Cd, Se and Zn decreased with increasing metal concentration, indicating that the seaweeds had a higher relative uptake at lower metal concentration. Uptake of Cd and Zn was higher in U. lactuca than in G. blodgettii, whereas uptake of Cr and Se was comparable between the two species. Only Cd and Zn uptake in U. lactuca was significantly inhibited by dark exposure. A decrease in salinity from 28 to 10‰ enhanced the uptake of Cd, Cr, Se and Zn in U. lactuca 1.9-, 3.0-, 3.6-, and 1.9-fold, respectively. In G. blodgettii, Cd uptake increased twofold when salinity was decreased from 28 to 10‰, whereas uptake of Cr and Zn was not significantly affected by salinity change. The calculated depuration rate constants of metals in U. lactuca were 0.01 d⁻¹ for Cd, 0.05 to 0.08 d⁻¹ for Cr, 0.14 to 0.16 d⁻¹ for Se, and 0.12 to 0.15 d⁻¹ for Zn, and were relatively independent of the metal body burden in the algae. The predicted bioconcentration factor was 3 × 10⁴ for Cd, 2 × 10³ for Cr, 40 to 150 for Se, and 1 to 2 × 10⁴ for Zn in U. lactuca. Our kinetic study suggested that U. lactuca would be a good biomonitor of Cr and Zn contamination in coastal waters. Received: 14 September 1998 / Accepted: 29 May 1999     

Photolytical property of L(+)-α-phenylglycine in aqueous solution

A wide range of pharmaceutical compounds have been identified in the environment, and their existence is a topic of growing concern, both for human and ecological health. The work described here has investigated the photolytic properties of L(+)-α-phenylglycine (L-α-PG-H) in aqueous solution as it can be degraded by photo-catalysis. In 266 nm laser flash photolysis of aqueous solution of L-α-PG-H saturated with nitrogen, two transient absorption bands are observed at 280–330 nm and 450–800 nm, respectively, due to L-α-PG-H radical cation and hydrated electrons (e_aq⁻). Then e_aq⁻ reacts with L-α-PG-H to form the L-α-PG-H radical anion. Decaying rate constants of e_aq⁻ observed at 720 nm is to be 8.9 × 10⁸ dm³ mol⁻¹ s⁻¹. The rate constant for oxidation of L-α-PG-H by SO₄ ⁻ is calculated as 4.5 × 10⁸ and 4.3 × 10⁸ s⁻¹ mol⁻¹ dm³, respectively. The dissociation constants (pKa) of L-α-PG-H is 3. Excited triplet of L-α-PG-H in solution is formed by laser flash photolysis. The quench rate constant of L-α-PG-H excited triplet (k _s) is determined to be 1.3 × 10⁷ dm³ mol⁻¹ s⁻¹ and k ₀ is equal to 1.7 × 10⁵ s⁻¹.     

Human risk assessment of As,Cd, Cu and Zn in the abandoned metal mine site

The cancer risk and the non-cancer hazard index for inhabitants exposed to As, Cd, Cu and Zn in the soils and stream waters of the abandoned Songcheon Au–Ag mine area were evaluated. Mean concentrations of As, Cd, Cu, Pb and Zn in agricultural soils were 230, 2.5, 120, 160, and 164 mg kg⁻¹, respectively. Mean concentrations of As, Cd and Zn of the water in the stream where drinking water was drawn was 246 μg L⁻¹, 161 μg L⁻¹ and 3899 μg L⁻¹, respectively. These levels are significantly higher than the permissible levels for drinking water quality recommended by Korea and WHO. The resulting human health risks to farmers who inhabited the surrounding areas due to drinking water were summarized as follows: (1) the non-cancer health hazard indices showed that the toxic risk due to As and Cd in drinking water were 10 and 4 times, respectively, greater than those induced by the safe average daily dosages of the respective chemicals. (2) the cancer risk of As for exposed individuals through the drinking water pathway was 5 in 1000, exceeded the acceptable risk of 1 in 10,000 set for regulatory purposes.     

Solid phase extraction and preconcentration of cobalt in mineral waters with PAR-loaded Amberlite XAD-7 and flame atomic absorption spectrometry

A simple, sensitive, accurate, and selective method for determination of ultratrace levels of Co is modified. The method is based on preconcentration of Co on the PAR-loaded Amberlite XAD-7 at pH 2.0 ± 0.2 for contact time as low as 45 min. The adsorbed cobalt was eluted with concentrated nitric acid and measured by flame atomic absorption spectrometry. Recoveries up to 90% were achieved. The optimized preconcentration method was applied to cobalt determination in natural mineral waters. The detection limit was found to be 0.1 ng mL⁻¹. The relative standard deviation was found to be 13% for 600 mL of 2.0 ng mL⁻¹, for 10 replicate preconcentration procedures. Cobalt concentrations in the studied water samples were found to be in the ranges of 0.5–3.5 ng mL⁻¹.     

Field based speciation of arsenic in UK and Argentinean water samples

A field method is reported for the speciation of arsenic in water samples that is simple, rapid, safe to use beyond laboratory environments, and cost effective. The method utilises solid-phase extraction cartridges (SPE) in series for selective retention of arsenic species, followed by elution and measurement of eluted fractions by inductively coupled plasma mass spectrometry (ICP-MS) for “total” arsenic. The method is suitable for on-site separation and preservation of arsenic species from water. Mean percentage accuracies (n = 25) for synthetic solutions of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA), and dimethylarsinic acid (DMA) containing 10 μg l⁻¹ As, were 98, 101, 94, and 105%, respectively. Data are presented to demonstrate the effect of pH and competing anions on the retention of the arsenic species. The cartridges were tested in the UK and Argentina at sites where arsenic was known to be present in surface and groundwaters, respectively, at elevated concentrations and under challenging matrix conditions. In Argentinean groundwater, 4–20% of speciated arsenic was present as MA and 20–73% as As^III. In UK surface waters, speciated arsenic was measured as 7–49% MA and 12–42% DMA. Comparative data from the field method using SPE cartridges and the laboratory method using liquid chromatography coupled to ICP-MS for all water samples provided a correlation of greater than 0.999 for As^III and DMA, 0.991 for MA, and 0.982 for As^V (P < 0.01).     

Biomass partitioning of benthic microbes in a Baltic inlet: relationships between bacteria, algae, heterotrophic flagellates and ciliates

 The structure of a benthic microbial food web and its seasonal changes were studied in the shallow brackish waters of the island of Hiddensee, northeastern Germany, at two sites in close proximity by monthly or bimonthly sampling from July 1995 to June 1996. Abundance and biomass of phototrophic and non-phototrophic bacteria, heterotrophic flagellates (HF) and ciliates as well as the biomass of microphytobenthos were determined in the upper 0.3 cm sediment layer. Abundance of organisms showed strong positive correlation with water temperature, with the exception of the bacteria. Non-phototrophic bacterial numbers ranged from 7 × 10⁸ to 6.7 × 10⁹ cells cm⁻³ and phototrophic bacterial abundance from 4 × 10⁷ to 2.7 × 10⁸. Heterotrophic protist abundance ranged from 8 × 10³ to 104 × 10³ ind cm⁻³ for HF and from 39 to 747 ind cm⁻³ for ciliates. The biomass partitioning demonstrated the primary importance of non-phototrophic bacteria (min. 0.83, max. 84.87 μg C cm⁻³), followed by the microphytobenthos (min. 1.32, max. 50.93 μg C cm⁻³). The heterotrophic protists contributed roughly the same fraction to the total microbial biomass, with the biomass of the HF being slightly higher (HF 0.23 to 1.76 μg C cm⁻³, ciliates 0.04 to 1.17 μg C cm⁻³). Taxonomic classification of the benthic HF revealed the euglenids to be the most important group in terms of abundance and biomass, followed by thaumatomastigids and kinetoplastids. Other important groups were apusomonads, cercomonads, pedinellids and cryptomonads. The structure of the HF assemblage showed strong seasonal changes with euglenids being the most abundant taxa in summer, while apusomonads and thaumatomastigids were predominant in winter. Similar to the pelagic microbial food web, benthic picophototrophic bacteria were occasionally abundant, and the feeding modes of heterotrophic protists exhibited a great variety (predominantly omnivores, bacterivores, herbivores or predators). Filter-feeding HF were of little importance. Contrary to the pelagic environment, a top-down control on total benthic bacterial numbers by HF seemed unlikely at the studied stations which were characterised by muddy sand. Received: 6 January 1999 / Accepted: 21 October 1999     

Water-soluble extracts of the diatom Thalassiosira rotula induce aberrations in embryonic tubulin organisation of the sea urchin Paracentrotus lividus

Eggs and embryos of the sea urchin Paracentrotus lividus were used as a model to study the effect at the cellular level of potential anti-mitotic compounds extracted from the diatom Thalassiosira rotula. Eggs and embryos incubated in a water-soluble diatom extract, corresponding to 5 × 10⁶ and 10⁷ cells ml⁻¹, were totally blocked (i.e. cell division was blocked) at the one-cell stage. At lower concentrations (2.5 and 1.25 × 10⁶ cells ml⁻¹), the first mitotic division was inhibited in 32 ± 26% and 25 ± 3.5% of the zygotes, respectively, demonstrating the dose-dependent effect of diatom extracts on sea urchin development. Immunofluorescence dyes, specific for DNA and α-tubulin subunits, were used to stain nuclei and microtubules in sea urchin embryos during various phases of development. Images with the confocal laser scanning microscope showed that tubulin was not organised in filaments at the sperm aster and cortex levels, and that the pronuclei were not fused in embryos incubated soon after fertilisation with water-soluble diatom extracts corresponding to 10⁷ cells ml⁻¹. At lower diatom-extract concentrations (4 × 10⁶ cells ml ⁻¹), fusion of the pronuclei occurred but the mitotic spindle was not formed. Microtubules were clearly de-polymerised and the chromatin appeared globular and compacted at the centre of the cell. A similar structure was observed for sea urchin embryos incubated with 0.1 mM colchicine, a potent anti-mitotic compound. When sea urchin embryos were incubated in water-soluble diatom extracts at different times prior to the first mitotic division, microtubules appeared de-polymerised at each step, from pronuclear fusion to telophase, and cell division was blocked. At the histological level, embryos incubated with 4 × 10⁶ cells ml⁻¹ diatom extract showed nuclear fragmentation without cytokinesis. The possible use of sea urchin embryos as a bioassay to test for other unknown compounds with cytotoxic activity in phytoplankton species is discussed. Received: 7 May 1998 / Accepted: 9 December 1998     

Irradiance and temperature regulation of oxygenic photosynthesis and O2 consumption in a hypersaline cyanobacterial mat (Solar Lake, Egypt)

 Short-term effects of temperature and irradiance on oxygenic photosynthesis and O₂ consumption in a hypersaline cyanobacterial mat were investigated with O₂ microsensors in a laboratory. The effect of temperature on O₂ fluxes across the mat–water interface was studied in the dark and at a saturating high surface irradiance (2162 μmol photons m⁻² s⁻¹) in the temperature range from 15 to 45 °C. Areal rates of dark O₂ consumption increased almost linearly with temperature. The apparent activation energy of 18 kJ mol⁻¹ and the corresponding Q ₁₀ value (25 to 35 °C) of 1.3 indicated a relative low temperature dependence of dark O₂ consumption due to mass transfer limitations imposed by the diffusive boundary layer at all temperatures. Areal rates of net photosynthesis increased with temperature up to 40 °C and exhibited a Q ₁₀ value (20 to 30 °C) of 2.8. Both O₂ dynamics and rates of gross photosynthesis at the mat surface increased with temperature up to 40 °C, with the most pronounced increase of gross photosynthesis at the mat surface between 25 and 35 °C (Q ₁₀ of 3.1). In another mat sample, measurements at increasing surface irradiances (0 to 2319 μmol photons m⁻² s⁻¹) were performed at 25, 33 (the in situ temperature) and 40 °C. At all temperatures, areal rates of gross photosynthesis saturated with no significant reduction due to photoinhibition at high irradiances. The initial slope and the onset of saturation (E _k = 148 to 185 μmol photons m⁻² s⁻¹) estimated from P versus E _d curves showed no clear trend with temperature, while maximal photosynthesis increased with temperature. Gross photosynthesis was stimulated by temperature at each irradiance except at the lowest irradiance of 54 μmol photons m⁻² s⁻¹, where oxygenic gross photosynthesis and also the thickness of the photic zone was significantly reduced at 40 °C. The compensation irradiance increased with temperature, from 32 μmol photons m⁻² s⁻¹ at 25 °C to 77 μmol photons m⁻² s⁻¹ at 40 °C, due to increased rates of O₂ consumption relative to gross photosynthesis. Areal rates of O₂ consumption in the illuminated mat were higher than dark O₂ consumption at corresponding temperatures, due to an increasing O₂ consumption in the photic zone with increasing irradiance. Both light and temperature enhanced the internal O₂ cycling within hypersaline cyanobacterial mats. Received: 30 November 1999 / Accepted: 11 April 2000     

Are barnacle larvae able to escape from the threat of UV?

Earlier laboratory experiments suggested that environmental levels of UV-B radiation can damage the eyes of barnacle naupliar larvae and impair their phototactic behaviors. However, since barnacle larvae may avoid UV by migrating to deeper waters, it is not known whether such impairment would actually occur under field conditions. For the first time, this study provides both field and laboratory evidences to show that prevailing UV-B in the natural habitat of barnacle larvae could be an important environmental factor affecting natural barnacle populations. We here showed that although barnacle nauplii may avoid UV-B irradiation by downward migration, the amount of UV energy (9.8 × 10⁻⁶ J) received by a naupliar eye during downward migration in the natural water column is within the same order of magnitude as the total energy (7.5 × 10⁻⁶ J) sufficient to cause damages to naupliar eye and impair their phototactic responses. It is possible that solar UV-B prevailing at shallow waters would pose a similar threat to other zooplankton species over large geographic scale.