Concentrations and amounts of methylmercury in water and fish in the limed and acid basins of a small lake

Three months after neutralization concentrations of methylmercury (MeHg) were higher in the water of the limed than in the control basin of a small lake. After two years, the concentrations in the limed basin were somewhat lower than in the control (0.056–2.19 ng L^?1 and 0.129–2.65 ng L^?1, respectively). The highest concentrations were found in the anoxic hypolimnia. The total amount of MeHg in the water mass of the lake varied from 19 to 68 mg, showing a drop after spring and autumn overturns and a maximum during stratification periods. The total Hg concentrations of fish in L. Iso Valkjärvi varied from 0.06 to 0.14 μg g^?1 (ww) in whitefish to 0.1 to 0.7 μg g^?1 in perch and to 0.2 to 1.4 μg g^?1 in pike. The total amount of MeHg bound in the fish of the lake was quite similar to that in the water column, 43 to 59 mg in 1990–1993, 33 to 47 mg of which was in the perch population.     

Seasonal variability in the Mercury speciation of Onondaga Lake (New York)

Dissolved and particulate Hg speciation was determined on four occasions in the Spring to Fall interval of 1989, at three depths of the water column of Onondaga Lake, New York; an urban system in which the sediments and fish flesh are contaminated with H_g. Species determined included total Hg (Hg_t), reactive (‘ionic’) Hg (Hg_i), monomethylmercury (CH₃HgX), elemental Hg (Hg°) and dimethylmercury (CH₃)₂Hg). Onondaga Lake was found to contain very high levels of Hg_t (2 to 25 ng L^?1 Hg), Hg_j (0.5 to 10 ng L^?1 Hg), and CH₃HgX (0.3 to 7 ng L^?1 Hg), which generally increased with depth in the lake. These concentrations represent a significant level of contamination, based upon comparisons with other polluted and pristine sites. Elemental Hg levels were typically about 0.05 ng L^?1 and (CH₃)₂Hg was near the limits of detection (?0.001 ng) L^?1 in most samples. The greatest CH₃HgX concentrations in the hypolimnion, as well as the largest gradients of both CH₃HgX and (Hg_t), were observed upon the first onset of stratification, in early summer. These concentrations did not become more pronounced, however, as stratification and H₂S levels in the hypolimnion increased throughout the summer. The very low concentrations of (CH₃)₂Hg in these MeHg and sulfide-rich waters calls into question the belief that CH₃HgX and H₂S will react to yield volatile dimethyl-mercury, which can then escape to the atmosphere by diffusion. Mercury speciation was highly dynamic, indicating active cycling within the lake, and an apparent sensitivity to changes in attendant Iimnological conditions that track the stratification cycle.     

25 years of fission product input to Lakes Superior and Huron

To assess the health significance of fission products in the upper Great Lakes, we have reviewed available data from 1963 to 1980 on ⁹⁰Sr, ¹²⁵Sb, ¹³⁷Cs, and ¹⁴⁴Ce concentrations in the water, sediments, and biota of Lakes Superior and Huron. Activities in water and sediment were compared with predictions based on fallout deposition over the past 25 yr. Estimates have also been derived of the removal half-times of the various fission products from lake water. There are indications that ¹³⁷Cs is re-entering water from sediment. The significance of the various pathways of fission products from the upper lakes system to man has been evaluated. The dose commitments from fission product concentrations over the past 25 yr give no basis for health concern. However, a large-scale release from a nuclear facility on the shore of a lake could have a measurable impact for many years to come.     

The distribution of nitrogen species in polluted Onondaga Lake,N.Y., U.S.A.

The temporal and vertical distributions of four N species, N0₃ ^?, NO₂ ^?, total ammonia (T-NH₃), and free ammonia (NH₃), are documented for Onondaga Lake, an urban, polluted, hypereutrophic, dimictic, lake that receives a very high load of T-NH₃. Nitrate and NO₂ ^? were lost rapidly from the hypolimnion, and T-NH₃ accumulated to high concentrations (maximum > 10 mgN L^?1), after the onset of anoxia, consistent with the lake's high level of productivity. The concentrations of T-NH₃, NH₃ and N0₃ ^? that were maintained in the epilimnion (average concentrations at a depth of 1 m of 2.81, 0.16 and 0.91 mgN L^?1, respectively), and concentrations of N0₂ ^? that developed in the epilimnion (maximum of 0.48 mgN L^?1), were high in comparison to levels reported in the literature. These elevated concentrations are largely a result of the extremely high loads of T-NH₃, and its precursors, received by the lake. Water quality problems in the lake related to the prevailing high concentrations of N species include potential toxicity effects and severe lake-wide oxygen depletion during fall turnover.     

Methylmercury production in the anoxic hypolimnion of a Dimictic Seepage Lake

Experimental results and field data indicated that methyl-Hg was produced within a layer of bacterioplankton near the top of the anoxic hypolimnion of Pallette Lake. In situ incubations at ambient Hg concentrations indicated that the net flux of methyl-Hg from the layer was between 50 and 100 pmol/m^2*d. This input was sufficient to account for the summer accumulation of methyl-Hg in the entire hypolimnion and it exceeded atmospheric inputs by 2 orders of magnitude. Maximum rates of net methylation occurred in the same region of the water column where we observed maximum rates of sulfate reduction. The measured rates were: 100 fmol rriethyl-Hg/L^*d and 90 nmol SO₄/L^*d. Sulfate reducing enrichment cultures isolated from the hypolimnion were also able to methylate Hg in the laboratory. Sulfate reduction did not occur in anoxic profundal sediments during summer and we infer from ancillary data that methylation in profundal sediments was also low. Whole-lake rates of sulfate reduction in the hypolimnetic layer and shallow sediments were roughly equivalent, but we cannot yet compare methylation rates at these sites due to large uncertainties in the littoral flux of methyl-Hg. We propose that zones of Hg methylation and SO4 reduction follow the oxic/anoxic boundary in both the watercolumn and sediments. The relative importance of watercolumn and sediment processes will depend on the physical and chemical structure of a given lake.     

Side Effects of Liming - A Study of Four Dimictic Lakes in Southern Norway

Side effects related to liming have been studied in four dimictic lakes (553–642 m?a.s.l.; 59°57′N) in Finnemarka, a forested area in Southern Norway with poor catchment buffer capacity. Data series from lake profiles have been sampled two decades apart; 10 years prior to liming and after 10 years of liming. Water samples were collected during spring after ice breakup and during summer after the development of thermal stratification. Before liming, there were very low concentrations of bicarbonate (HCO ₃ ^– ; or alkalinity) in the lakes. After 10 years of liming, up to 90% of the ions in hypolimnion originate from lime products. Hence, liming strengthened the chemical stratification and increased the vertical stability. Differences in chemocline developments between lakes were explained by differences in physical properties, i.e. their depth/surface area ratio. The chemocline developments lead to increased concentrations of organic matter in the hypolimnion with a subsequent reduction in oxygen concentrations. Lime additions during late spring, as an alternative to early autumn, lead to pronounced anoxic conditions in the hypolimnion.     

Mercury Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). I: In-lake Processes

The processes affecting the concentrations of total mercury (total Hg) and methylmercury (MeHg) in a freshwater system comprising two connected reservoirs in southwest Tasmania were investigated. Surface concentrations of total mercury (total Hg)were temporally and spatially uniform in both Lake Gordon (2.3±0.4 ng L^-1, n = 27) and Lake Pedder (2.3±0.3 ng L^-1, n = 11). The surface concentrations of MeHg in Lake Gordon (0.35±0.39 ng L^-1, n = 25) were more variable than total Hg and MeHg typically comprised 10–20% of total Hg. The relatively high amount of total mercury present as MeHg in Lake Gordon was attributed to the high proportion of wetlandsin the upper catchment (50% of total area) and in-lake contributions (ca. 40% of total MeHg). Despite the close proximity of the two lakes, MeHg concentrations in Lake Pedder were consistently lower than in Lake Gordon. This phenomenon canbe explained in part by the greater contribution of direct rainfall to Lake Pedder leading to the dilution of MeHg. Water column MeHg concentrations were higher in warmer months in bothlakes, reflecting increased net methylation of inorganic mercury.Unlike previous studies of seasonally anoxic lakes, depth profiles of total mercury and MeHg in Lake Gordon were uniform and were not affected by water column stratification occurringin the summer months, and oxygen depletion with depth. This suggests that redox cycling and accumulation of MeHg in the hypolimnion following seasonally-induced anoxia is not a significant part of the mercury cycle in Lake Gordon. The primary location of MeHg production within the lake's water column is not conspicuous. Mercury speciation measurements made above and below the lake system over a period of 19 months indicates that after 20 yr of impoundment, the reservoirs are not significantly affecting MeHg concentrations in the downstreamriverine environment.     

Phosphorus Dynamics in a Small Eutrophic Italian Lake

Phosphorous dynamics within Lake Sirio (NW Italy) were investigated, considering both water and sediments. The total phosphorus (TP) concentration in the water is about 79 μg l^?1 after the winter mixing, that is in homogeneous conditions; then TP content increases up to an average of 360 μg l^?1 in late autumn in the deep hypolimnium (30–45 m). This deep lake portion accounts for only 1/12 of the water volume. Close to the water-sediment interface, TP concentrations up to 530 μg l^?1 are observed. Sediment sampled at depths of 20 and 33 m contains less than 2,000 mg kg^?1 of TP, whereas cores from the deepest sediments (46 m) display TP values of 2,000–4,000 mg kg^?1 at the water-sediment interface, increasing with depth to 16,000 mg kg^?1 at about 60–100 cm. In these deep sediments the main chemical form is the Al–Fe–Mn bound P (about 90% in the high TP cores) and Fe and Mn are also highly enriched (3 and 9 times more than in the shallow sediments respectively). The P–Fe association is confirmed by SEM-EDS and XRD analyses. The vertical distribution of the P content in the water column is consistent with its release from sediments, but in this hypothesis an unrealistic P release rate from 8.1 to 3.0 g m^?2y^?1 was estimated. A more complex model is therefore proposed, involving a process of P concentration in the sediments of the central (deepest) part of the lake, and a short term sediment-water exchange. The TP vertical variability and speciation in the cores suggests a change in the sediment retention capacity, connected to the lake shift to more eutrophic conditions.     

Accumulation of radioactive cesium in sorghum (Sorghum bicolor (L.) Moench) accessions cultivated in Fukushima in 2011 and 2012

ABSTRACT

The accident at Fukushima 1 Nuclear Power Plant in 2011 caused contamination by radioactive cesium (¹³⁴Cs and ¹³⁷Cs) in surrounding areas. After this accident, concerns about Cs contamination, including food safety, have limited industrial activities and reconstruction in Fukushima. Sorghum (Sorghum bicolor (L.) Moench) is an annual C₄ crop that can be used as biofuel feedstock due to its high biomass. Use of Cs-contaminated fields to produce biofuel feedstock would be more acceptable than use for food or feed crops due to the lower risk of human internal exposure to radioactive Cs. In addition, high-biomass sorghum might be suitable for removal of Cs from fields (phytoremediation). For both applications, it is important to use accessions showing the appropriate level of accumulation of radioactive Cs (low for biofuel feedstock, high for phytoremediation). Here, we examined the accumulation of radioactive Cs in the aerial parts of 56 sorghum accessions grown in Fukushima. Accessions were cultivated in a low-level-contaminated field in 2011 and in a highly contaminated field in a planned evacuation zone in 2012. After cultivation, activity concentrations from ¹³⁴Cs and ¹³⁷Cs were measured in the aerial plant parts. In 2011, the activity concentrations of ¹³⁴Cs and ¹³⁷Cs were 58.2–350 and 58.6–450 Bq kg^?1 dry weight, respectively. In 2012, the concentrations of ¹³⁴Cs and ¹³⁷Cs were 54.2–1320 and 57.1–1960 Bq kg^?1 dry weight, respectively. Relative to the median values of the accessions grown each year, 3 showed lower activity concentrations and 2 showed higher activity concentrations of radioactive Cs under both cultivation conditions. In contrast to a previous report, there was no significant correlation between biomass and Cs activity concentration. Because both biomass and Cs concentration are important in classifying accessions for use in phytoremediation, we also calculated the Cs accumulation index (single-plant biomass × Cs activity concentration) for each accession. The accession AKLMOI WHITE showed the highest values in both years, suggesting that this accession has the high per-plant accumulation capacity for radioactive Cs. Our data collected from actual contaminated fields is irreplaceable for choosing sorghum accessions for cultivation in Cs-polluted sites such as Fukushima.     

Climate Change as the Primary Cause for pH Shifts in a High Alpine Lake

Chemical and biological sedimentary records of a high alpine lake were used to reconstruct palaeoecological conditions and compared with two centuries of instrumental temperature measurements. Air temperature determined the lake water pH throughout the past 200 yr almost regardless of the level of atmospheric deposition. Our data suggest a strong climate forcing of the acid-base balance in sensitive high-altitude lakes. Their physico-chemical conditions and biota strongly depend on the duration of ice and snow cover which is significantly different between warm and cold periods. Beside changes in weathering rates, in-lake alkalinity generation and water-retention time, delayed freezing in autumn and earlier ice-out dates with a shorter duration of CO₂ over-saturation could be crucial for the tight temperature-pH coupling.     

Mercury speciation in Lake Baikal

Research on mercury (Hg) distribution and speciation was carried out in Lake Baikal, a large, strong-oligotrophic freshwater reservoir in Siberia, Russia, during June 1992 and march 1993. In summer, total Hg in the water column ranged from 0.14 to 0.77 ng Hg/L, with the highest concentrations observed in the central basin of the lake in surface water samples. Labile inorganic Hg was found to be 7 to 20 % of the total Hg content. Highest total Hg concentrations were found in river waters: up to 2 ng Hg/L. Labile methylmercury (MeHg) concentrations ranged from 2 to 38 pg Hg/L in the water column, with the higher concentrations in the central part of the lake, and showing a slight increase in near bottom waters. Labile MeHg makes up 1 to 15 % of the total Hg content in the water column, with larger fractions in deep waters. The slight increase of the MeHg gradient with depth corresponds with the O₂ minimum region. Highest MeHg concentrations were observed in river waters (up to 145 pg Hg/L) and in some bays of the lake (up to 160 pg Hg/L). In these high temperature- and phytoplankton-rich water masses, the MeHg-fraction increased up to 35 % of total Hg. Labile MeHg concentrations in water samples taken in winter in the southern basin (under the ice cover), showed slightly higher concentrations than in summer, possibly due to an early spring bloom. In rainwater, total Hg ranged from 3 to 20 ng Hg/L and MeHg from 0.1 to 0.25 ng Hg/L. In snow, a large fraction of total Hg is bound to particulate matter; concentrations of total Hg ranged from 8 to 60 ng Hg/L and labile MeHg from 0.1 to 0.25 ng Hg/L. Atmospheric Hg was found to be 0.73 to 2.31 ng/m³ as gaseous Hg and 0.005 to 0.02 ng/m³ in its particulate form. Spatial distribution patterns of atmospheric Hg show slightly higher concentrations over the central part of the lake and the Selenga river delta. In winter, atmospheric Hg values (measured in the southern region), ranged from 1.2 to 6.1 ng/m³ as total gaseous Hg and 0.02 to 0.09 ng/m³ as total particulate Hg, and are higher than in summer, probably influenced by coal burning and traffic by the local population. MeHg contents in fish ranged from 20 ng Hg/g dry weight in small Cottocomephorus to 300 ng Hg/g dry weight in pike and trout species, which were caught in organic-rich waters.     

Radioactive cesium distribution in bamboo [Phyllostachys reticulata (Rupr) K. Koch] shoots after the TEPCO Fukushima Daiichi Nuclear Power Plant disaster

Abstract

Radioactivity levels of cesium (Cs)-134 and ¹³⁷Cs in bamboo [Phyllostachys reticulata (Rupr) K. Koch] sprouts grown from April to June 2011 over a wide area (including Fukushima Prefecture) were elevated (max. 3100 Bq kg^?1 fresh weight) after the Tokyo Electric Power Company, Inc. (TEPCO) Fukushima Daiichi Nuclear Power Plant disaster in March 2011. Bamboo sprouts in 2012 also contained high radioactivity levels. Radioactivity imaging analysis of bamboo sprouts harvested in 2012 showed increasing concentration gradients of radioactivity from the lower parts to the top of the sprouts. The peels were individually separated from the sprouts, and the inner edible part (trunk) was cross-sectioned at the internodal sections from the top to the lower parts. Each segmented trunk and its corresponding peel were analyzed for radioactive cesium (¹³⁴Cs and ¹³⁷Cs) and stable cesium (¹³³Cs). The concentrations of ¹³⁴Cs and ¹³⁷Cs showed significant increases from the lower part to the top, whereas ¹³³Cs showed an almost constant value in the trunk and peel except in the peel of the top node. We speculated that ¹³⁴Cs and ¹³⁷Cs in newly emerging bamboo sprouts in 2012 were translocated mainly from various plant tissues (where the fallout was layered on the bamboo tissues) in older bamboo, while ¹³³Cs was translocated from the soil through the roots of the new bamboo sprouts and was present in the roots and stems.     

Mercury in fish in the Smallwood Reservoir,Labrador, twenty one years after impoundment

The elevated mercury (Hg) levels in fish flesh found after impoundment of a reservoir, are predicted to decline as the reservoir ages. The length of time required for a return to background levels is dependent on among other things, the trophic status of the fish. Predictions for omnivorous species range between 15 and 20 years while for piscivorous species they vary from 20 to 30 years. Fish in the Smallwood Reservoir, Labrador, Canada, were sampled 6 years after impoundment when hg levels were found to be elevated in most species. Selected of the sites were re-sampled after 16 years and again after 21 years. Mercury in the flesh of omnivorous species such as lake whitefish (Coregonus clupeaformis) had returned to background levels after 16 years as predicted. However, hg in the flesh of piscivores such as northern pike (Esox lucius) and lake trout (Salvelinus namaycush) remained elevated even 21 years after impoundment. While the levels in lake trout have declined somewhat in that time, there is no evidence of decline in the northern pike either within the reservoir or at downstream stations. Models predicting decline in hg levels in piscivorous fish in reservoirs must be re-evaluated in light of this extended data set.     

Chronology of Anthropogenic Heavy-Metal Fluxes and Pb Isotope Ratios Derived from Radiometrically Dated Lake Sediments in Northern Germany

Anthropogenic inventories and fluxes of Pb, Zn, Cu, and Sninto the sediments of two lakes, a drinking water reservoir(Neumühler See) and an urban lake (Ziegelsee), both in ornear Schwerin, Germany, were investigated. A simplefreeze-coring technique was used for reproducible samplingof undisturbed surface sediments. Sediment chronology wasestablished for Ziegelsee by gamma spectrometry of thenuclides ¹³⁴Cs, ¹³⁷Cs, ²⁴¹Am, ²¹⁴Pb,²¹⁴Bi and ²¹⁰Pb; bioturbation in Neumühler Seeprevents this. Anthropogenic heavy-metal loads weredetermined using Co as tracer for the geogenic portion. Anthropogenic heavy-metal inventories of Ziegelsee exceedthose of Neumühler See by factors of 3.0, 6.0, 5.6, and 6.8for the heavy metals Pb, Cu, Zn, and Sn, respectively. Theanthropogenic Pb flux into Ziegelsee increased from 1870 to1965 and decreased below the 1870 level by 1990. Isotoperatios of anthropogenic Pb change with time and indicatedifferent sources (lignite, gasoline). The anthropogenicCu, Zn, and Sn fluxes into Ziegelsee with respect to timeare comparable to that of Pb, but between 1960 and 1980pronounced local peaks appear and this was not determinedin the Pb flux.     

The influence of trophic level as measured by δ15N on mercury concentrations in freshwater organisms

The relationship between mercury (Hg) concentrations in freshwater biota and trophic position, as defined by stable nitrogen isotope ratios (δ¹⁵N), was examined in 6 lakes in northwestern Ontario. The heavier isotope of nitrogen (¹⁵N) increases an average of 3 parts per thousand (‰) from prey to predator and is used as a measure of an organism's trophic position. Dorsal muscle from lake trout, burbot, walleye, northern pike, white sucker, lake cisco, lake whitefish, and yellow perch was analyzed for Hg and δ¹⁵N using flameless atomic absorption and mass spectrometry respectively. Within each lake, log Hg was significantly related to δ¹⁵N (r ² ranged from 0.47 to 0.91,P<0.01). For four species, yellow perch, northern pike, lake cisco, and lake trout, log Hg was positively related to δ¹⁵N (r ² ranged from 0.37 to 0.47,P≤0.09) across all lakes. We also used δ¹⁵N measurements (assuming a 3‰ shift between an organism and its diet) and the developed within-lake regression equations to calculate a prey Hg for each individual fish. These food Hg values were then used to predict predator Hg using Norstromet al's bioenergetics model. Predicted results were strongly correlated to measured Hg concentrations (r=0.91,P<0.001), indicating that δ¹⁵N has potential to be used in modeling.     

Mercury in Small Freshwater Lakes: A Case Study: Lake Velenje, Slovenia

Lake Velenje is located in one of the most polluted regions ofSlovenia, the ?alek Valley. The major source of pollution is the coal-fired thermal power plant in ?o?tanj (?TPP). In the past, dumping of coal ash directly into Lake Velenje and drainage water from the ash disposal site resulted in unique chemical characteristics of the lake water, such as very high pH (10–12) and high concentrations of heavy metals. The introduction of a closed cycle ash transport system in 1995resulted in a very fast recovery of the lake water quality. The aim of our study was to establish the sources, fate and distribution of mercury in Lake Velenje. In order to establishrecent sources of mercury, total mercury and methylmercury concentrations were measured in various environmental samples(lake inflows, outflow, rainwater, sediments, etc.). Total mercury and methylmercury concentrations were measured at thesurface and at different depths to establish mercury cycling, its transport and chemical transformations in the lake. Generalwater quality parameters (such as pH, Eh, O₂, temperature,TDS, conductivity) were also determined. The results show that the major sources of mercury in Lake Velenje are lake inflows and wet deposition. Total mercury andmethylmercury concentrations in the water column are very low (total mercury: 0.2–2.7 ng L^-1; methylmercury: 20–86 pg L^-1) and can be compared to other non-contaminated freshwater lakes. These results suggest that the major form of mercury emitted from thermal power plant stacks is volatile Hg⁰, whichhas no or very little influence on the nearby surroundings, but rather is subject to long-range atmospheric transport.     

The impact of a chlor-alkali plant on Onondaga Lake and adjoining systems

The pervasive effects an adjoining chlor-alkali plant has had on Onondaga Lake, and the river system that receives the lake discharge, are documented. Effects of the ionic waste discharge of the facility include: (1) ionic enrichment, (2) altered stratification regimes, (3) altered exchange between the lake and river, (4) altered hydrodynamics in the river downstream of the lake, (5) precipitation and deposition of large quantities of calcium carbonate, and (6) altered chemistry of lake sediments regulating P availability. Mercury, benzene, chlorobenzene wastes from the plant have contaminated the sediments and fish of the lake. Deleterious effects of the facility have included: the elimination of fish habitat, exacerbation of the problem of limited Oz resources of the hypolimnion, contamination offish flesh, exacerbation of the problem of low transparency of the lake, and severe O₂ depletion in the lower waters of the river system.     

Mercury in Lake Vänern, Sweden Distribution In Surface Sediment And Catchment Budget

Lake Vänern is Sweden's largest lake and freshwater reservoir. Large quantities of mercury were released into the lake during a large part of the 20th century, resulting in serious contamination. The main load originated from one single point source — a chlor-alkali industry. Its releases were drastically reduced in the early 1970's, but nearby sediments displayed alarmingly high concentrations. During summer 2001, fifty-one sediment cores were taken, and analysed for total mercury. It was found that mercury concentrations in surface sediments have decreased significantly between 1974 and 2001, but the influence of the former single point source was still reflected in the concentration patterns. Thirty years ago, sediments around the dominant point source displayed the highest concentrations. Today, the highest concentrations in surface sediments were still found close to it, but also in deep waters in the central part of the lake. Surprisingly, the gradient from the point source is stronger today compared to 1974. A mercury budget, based on the annual sediment accumulation rate, the bulk density, atmospheric load and outflow of mercury, was formed. The surface sediments (0—1 cm, on average corresponding to ～5 yr according to ¹³⁷Cs dating) in accumulation bottoms (water depth >40m) contained approximately 530 kg Hg (corresponding value for year 1974 was 4100 kg Hg). A majority of the present additions of mercury to the lake originates from atmospheric deposition. It was also found that the lake acts as a sink for mercury. In fact, approximately 90—95% of the incoming mercury was retained within the catchment or in the sediments.     

Age-Dependent Bioaccumulation of Organochlorine Compounds in Fish and their Selective Biotransformation in Top Predators from Lake Maggiore (Italy)

Fish and piscivorous bird eggs collected in 2003 from Lake Maggiore (Italy), were analysed for PCB and DDT contamination. Lake Maggiore has been severely polluted by DDT through production of the pesticide within its catchment. Although agricultural application of DDT was banned in Italy in the 1978, industrial production continued until 1996, with enough contamination of water and soil for serious bioaccumulation in the lake biota. PCB and DDT concentrations in a whitefish (Coregonus macrophthalmus Nusslin 1882) were seen to be dependent on season and fish age, but not on sex. The average increase of the lipid-normalised concentration of DDTs and PCBs was two-fold across season and also across age, resulting in an overall increase of four fold. The seasonal variation was related to the eco-physiological cycle of the fish and to the contamination dynamic of the lake, while the effect of the fish age was explained on the base of biomagnification-related mechanisms. A fugacity model was applied to predict the age-dependent bioaccumulation potential of PCBs, whose concentrations were rather stable in recent years in the lake. Predicted values for compounds with negligible biotransformation were in good agreement with experimental data (calculated vs. experimental mean difference of 14%), and a relationship between the increase of experimental age-dependent concentration and K _ow was observed. The good correspondence between the predicted and the measured values for most PCB congeners confirmed the general inability of fishes to biotransform these compounds. On the contrary, the importance of biotransformation processes was recognised in birds; eggs of a fish eating bird (Podiceps cristatus) from the same area selectively bioaccumulated p,p′-DDE. For PCBs, congener 149 appears to be completely metabolized by the bird species, and congeners 95, 101, 132, 151 and 174 were reduced as well. The role of the meta–para free position on at least one phenyl ring of PCB congeners in biotransformation processes was confirmed.     

Potassium bentonites reduce radiocaesium availability to plants

After the Chernobyl accident in 1986 the fate of radiocaesium from the fallout became of pressing concern. Specific soil amendments, as K fertilizer and specific clay minerals, promised to mitigate the worst effects. We therefore investigated the influence of bentonite and the K status of the soil on the radiocaesium equilibria in soil and on its availability to ryegrass. A sample of a sandy soil was contaminated with ¹³⁴Cs and amended with K and Ca salts (0–0.97 mmol kg^?1) and K bentonite (0–2%). After 4 weeks' incubation of the soil mixtures, ryegrass was grown for 18 weeks in a pot trial and harvested on seven occasions. No significant treatment effects on ¹³⁴Cs activity concentrations were found at the first and second harvest. From the third harvest onwards, however, ¹³⁴Cs activity concentrations in the grass were reduced up to twofold (P < 0.05) by increasing rates of K bentonite. Adsorption studies with ¹³⁷Cs revealed that the radiocaesium interception potential (RIP) of the soil–bentonite mixtures (> 1% bentonite) increased about 10‐fold during plant growth. The RIP of the K bentonite after plant growth was up to 10 times larger than that of pure illite. The formation of specific Cs sorption sites is ascribed to the in situ illitization of the K bentonite. The increase in RIP during plant growth is reflected in a decrease in exchangeable K⁺ at 2% K bentonite of about 18%. Radiocaesium concentrations in grass could be reliably predicted from the Cs⁺ and K⁺ concentrations in the soil solution. Adding K bentonite to a soil contaminated with radiocaesium is effective in fixing Cs in the soil.