Heavy metal capture from the suspended particulate matter by Morus alba and evidence of foliar uptake and translocation of PM associated zinc using radiotracer (65Zn).

In urban set up, increasing combustion and processing activities have contaminated the air with toxic heavy metals which are generally enriched on atmospheric particulate matter. Vegetation around urban area act as a sink where such metal enriched particles generally deposit on the foliar surfaces, however, role of vegetation in uptake of metals adhered on the atmospheric particulate matter is yet not explored properly and is important to study to evaluate their role as bio-remediator. The undertaken work examines the foliar surface of Morus alba for its potential to deposit and accumulate atmospheric heavy metals. Further, to understand foliar uptake mechanism and translocation of atmospheric metal enriched on particulate matter a simulated experiment was conducted by labeling the known particle size (45 µm and 120 µm) with radio labeled 65Zn, applied on the tagged leaf with two particle loads, 25 mg and 50 mg. The study showed that owing to its rough foliar surface with trichomes and grooves, Morus alba efficiently trap heavy metal enriched particles and was capable of accumulating metals from particulate matter into different plant parts. It was recorded that 65Zn adhered on different size particles was taken up by tagged leaf of mulberry and majorly translocated to the lower stem and roots. It was also inferred from the study that both particle size and particle load significantly affect the foliar uptake and translocation of atmospheric heavy metal. The study focuses on the fact that urban avenue trees are capable of taking up atmospheric heavy metals and can play a crucial role in improving air quality.

Regulation of biokinetics of (65)Zn by curcumin and zinc in experimentally induced colon carcinogenesis in rats.

This study was conducted to investigate the role of curcumin and zinc on the biokinetics and biodistribution of (65)Zn during colon carcinogenesis. Male wistar rats were divided into five groups, namely normal control, 1,2-dimethylhydrazine (DMH) treated, DMH + curcumin treated, DMH + zinc treated, and DMH + curcumin + zinc treated. Weekly subcutaneous injections of DMH (30 mg/kg body weight) for 16 weeks initiated colon carcinogenesis. Curcumin (100 mg/kg body weight orally) and ZnSO4 (227 mg/L in drinking water) were supplemented for 16 weeks. This study revealed a significant depression in the fast (Tb1) and slow component (Tb2) of biological half-life of (65)Zn in the whole body of DMH-treated rats, whereas liver showed a significant elevation in these components. Further, DMH treatment showed a significant increase in the uptake values of (65)Zn in colon, small intestine, and kidneys. Subcellular distribution depicted a significant increase in (65)Zn uptake values in mitochondrial, microsomal, and postmicrosomal fractions of colon. However, curcumin and zinc supplementation when given separately or in combination reversed the trends and restored the uptake values close to normal range. Our study concludes that curcumin and zinc supplementation during colon carcinogenesis shall prove to be efficacious in regulating the altered zinc metabolism.

Synthesis, characterization and in vivo evaluation of [(62)Zn]-benzo-δ-sultam complex as a possible pet imaging agent.

OBJECTIVE: The development of a new tracer based on the cyclic sulfonamides (sultams) was investigated. METHODS: 3-(Methoxy-phenyl-methyl)-1,6-dimethyl-1H benzo[c][1,2] thiazine 2,2-dioxide (benzo-δ-sultam) was synthesized and characterized by elemental analysis, FT-IR spectroscopy and single crystal X-ray structure determination. The prepared cyclic sulfonamide was labeled with non-commercial (62)Zn radioisotope for fast in vivo targeting and Coincidence imaging purposes (radiochemical purity 97 % ITLC, 96 % HPLC, specific activity 20-23 GBq/mmol). In vivo biodistribution of the final complex was investigated in Sprague Dawley(®) rats bearing fibro sarcoma tumor after 2, 4 and 8 h post injection and compared with free Zn(+2) cation. RESULTS: Using instant paper chromatography method, the physicochemical properties of labeled compounds were found sufficiently stable in organic phases, e.g. a human serum, to be reliably used in bioapplications. CONCLUSIONS: The complex exhibited a rapid as well as high tumor uptake (tumor to blood ratio 4.38 and tumor to muscle ratio 9.63) resulting in an efficient tumor targeting agent.

Selective uptake, distribution, and redistribution of (109)Cd, (57)Co, (65)Zn, (63)Ni, and (134)Cs via xylem and phloem in the heavy metal hyperaccumulator Solanum nigrum L.

The focus of this article was to explore the translocation of (109)Cd, (57)Co, (65)Zn, (63)Ni, and (134)Cs via xylem and phloem in the newly found hyperaccumulator Solanum nigrum L. Two experiments with the uptake via the roots and transport of (109)Cd, (57)Co, and (65)Zn labeled by roots, and the redistribution of (109)Cd, (65)Zn, (57)Co, (63)Ni, and (134)Cs using flap label in S. nigrum in a hydroponic culture with a standard nutrient solution were conducted. The results showed that (109)Cd added for 24 h to the nutrient medium of young plants was rapidly taken up, transferred to the shoot, and accumulated in the cotyledons and the oldest leaves but was not efficiently redistributed within the shoot afterward leading to a rather low content in the fruits. In contrast, (57)Co was more slowly taken up and released to the shoot, but afterward, this element was redistributed from older leaves to younger leaves and maturing fruits. (65)Zn was rapidly taken up and transferred to the shoot (mainly to the youngest leaves and not to the cotyledons). Afterward, this radionuclide was redistributed within the shoot to the youngest organs and finally accumulated in the maturing fruits. After flap labeling, all five heavy metals tested ((109)Cd, (57)Co, (65)Zn, (63)Ni, (134)Cs) were exported from the labeled leaf and redistributed within the plant. The accumulation in the fruits was most pronounced for (63)Ni and (65)Zn, while a relatively high percentage of (57)Co was finally found in the roots. (134)Cs was roughly in the middle of them. The transport of (109)Cd differed from that previously reported for wheat or lupin and might be important for the potential of S. nigrum to hyperaccumulate cadmium.

Supplementation of zinc mitigates the altered uptake and turnover of 65Zn in liver and whole body of diabetic rats.

Diabetes is a life threatening disease and its onset is linked with both environmental and genetic factors. Zinc metabolism gets altered during diabetes and results in many complications. The present study was designed to elucidate the effects of zinc supplementation on the biokinetics of (65)Zn in whole body, liver and its biodistribution in diabetic rats. The animals were divided into four groups viz; normal control; diabetic (single intraperitoneal injection of alloxan 150 mg/kg body weight); zinc treated (227 mg/l in drinking water); and diabetic + zinc treated. To carry out biokinetics study, each rat was injected intraperitoneally with 0.74 MBq radioactivity of (65)Zn following 4 weeks of different treatments and the radioactivity was determined by using a suitably shielded scintillation counter. Alloxan induced diabetic rats showed a significant decrease in both the fast (Tb(1)) and slow (Tb(2)) components of biological half-life of (65)Zn which, however, were normalized in whole body (P > 0.05) following zinc supplementation. In case of liver, Tb(2) component was brought back to the normal but Tb(1) component was not increased significantly. The present study indicates that the paucity of zinc in the tissues of the diabetic animals was due to decreased retention of tissue zinc as evidenced by increased serum Zn, hyperzincuria and increased rate of uptake of (65)Zn by the liver. Zinc supplementation caused a significant improvement in the retention of zinc in the tissues and is therefore likely to be of benefit in the treatment of diabetes.

Regulatory role of zinc on the biokinetics and biodistribution of (65)Zn during the initiation of experimentally induced colon cancer.

The present study was conducted to evaluate the kinetics of zinc utilization during the formation of colon carcinoma in an animal model of colon carcinogenesis. The rats were segregated into 4 groups: untreated control, 1,2-dimethylhydrazine (DMH) treated, zinc treated, and DMH+zinc treated. Colon carcinogenesis was initiated through weekly subcutaneous injections of DMH (30 mg/kg body weight) for 8 wk. Zinc (in the form of zinc sulphate) was supplemented at a dose level of 227 mg/L in drinking water, ad libitum for the entire duration of study. Whole body (65)Zn kinetics followed two-compartment kinetics, with Tb(1) representing the initial fast component of the biological half-life and Tb(2), the slower component. The Tb(1) component showed a significant elevation while the Tb(2) component was significantly diminished in DMH-treated rats, which, however, got normalized following zinc supplementation. The biodistribution and subcellular distribution of (65)Zn was significantly affected in DMH-treated rats when compared to normal control rats. However, zinc significantly reversed the altered (65)Zn uptake in different organs and various fractions of colon. The present study for the first time demonstrated a faster mobilization of zinc during initiation of experimentally induced colon carcinoma and provides a physiological basis for the role of zinc in colon tumorigenesis.

Polyphenol-rich beverages enhance zinc uptake and metallothionein expression in Caco-2 cells.

The effect of red wine (RW), red grape juice (RGJ), green tea (GT), and representative polyphenols on Caco-2 cell (65)Zn uptake was explored. RW, RGJ, and GT enhanced the uptake of zinc from rice matrix. Fractionation of RW revealed that enhancing activity of zinc uptake was exclusively resided in the polyphenol fraction. Among the polyphenols tested, only tannic acid and quercitin stimulated the uptake of zinc while others did not influence the uptake. In tune with these results, only tannic acid and quercitin competed with zinquin (a zinc selective fluorophore) for zinc in vitro. Although all the polyphenols tested appear to enhance the expression of metallothionein (MT), the induction was higher with tannic acid, quercitin, and RW extract. Furthermore, phytic acid abrogated the tannic acid-induced MT expression. These results suggest that polyphenol-rich beverages, tannic acid, and quercitin bind and stimulate the zinc uptake and MT expression in Caco-2 cells.

65Zn kinetics as a biomarker of DMH induced colon carcinogenesis.

Dietary factors are considered crucial for the prevention of initiating events in the multistep progression of colon carcinoma. There is substantial evidence that zinc may play a pivotal role in host defense against several malignancies, including colon cancer. The present study was conducted to evaluate the kinetics of (65)Zn utilization following experimental colon carcinogenesis in rat model. Twenty rats were segregated into two groups viz., untreated control and dimethylhydrazine (DMH) treated. Colon carcinogenesis was established through weekly subcutaneous injections of DMH (30 mg/kg body weight) for 16 weeks. Whole body (65)Zn kinetics followed two compartment kinetics, with Tb(1) representing the initial fast component of the biological half-life and Tb(2), the slower component. The present study revealed a significant depression in the Tb(1) and Tb(2) components of (65)Zn in DMH treated rats. Further, DMH treatment caused a significant increase in the percent uptake values of (65)Zn in the colon, small intestine, kidney and blood, whereas a significant decrease was observed in the liver. Subcellular distribution revealed a significant increase in (65)Zn uptake in the mitochondrial and microsomal fractions following 16 weeks of DMH supplementation. In conclusion, the present study demonstrated a slow mobilization of (65)Zn during promotion of experimentally induced colon carcinogenesis and provides a physiological basis for the role of (65)Zn in colon tumorigenesis, which may have clinical implications in the management of colon cancer.

Uptake and retention of 65Zn in lithium-treated rat liver: role of zinc.

AIM: To evaluate the effects of zinc on the biokinetics of (65)Zn in rat and its distribution in various organs and in subcellular compartment following lithium therapy. METHODS: Female wistar rats received either lithium treatment at a dose of 1.1g/kg in diet, zinc alone at a dose of 227 mg/L in drinking water, and combined lithium plus zinc for duration of four months. RESULTS: After four months of lithium treatment, liver enzymes increased significantly (glutamic oxaloacetic transaminase, +66.73%; glutamic pyruvic transaminase, +63.70%; alkaline phosphatase, +40.28%; p< or =0.001); zinc supplementation to lithium-treated rats significantly reduced liver enzymes (glutamic oxaloacetic transaminase, -13.11%; glutamic pyruvic transaminase, -21.78%; alkaline phosphatase, -11.77%; p< or =0.001). The biological half-lives of (65)Zn showed an initial fast component (Tb(1)) and a slower component (Tb(2)). A significant increase in Tb(2) (38.82%, p< or =0.001) in liver was observed following lithium treatment, which significantly decreased following zinc treatment (21.71%, p< or =0.001). A significant decrease in the uptake of (65)Zn (53.93%, p< or =0.01) in liver was observed and in nuclear (p< or =0.01), mitochondrial (p< or =0.01), and microsomal (52.67%, p< or =0.001) fractions. A significant increase in the uptake of (65)Zn (82.92%, p< or =0.05) in liver microsomal fraction (34.09%, p< or =0.001) was observed in lithium-treated rats receiving zinc supplementation. CONCLUSION: The study suggests that zinc has the potential to regulate the biokinetics of (65)Zn and its subcellular distribution in rat liver following lithium therapy.

Zinc retention differs between primary and transformed cells in response to zinc deprivation.

Previous studies in our laboratory have demonstrated that reducing the availability of zinc with the extracellular metal chelator DTPA (diethylenetriaminepentaacetate) enhances, rather than inhibits, the thyroid hormone induction of growth hormone mRNA in GH3 rat anterior pituitary tumor cells. To understand the actions of the chelator on cellular zinc status, we observed the effects of DTPA on (65)Zn uptake and retention. DTPA reduced the uptake of (65)Zn by GH3 cells from the medium, but when GH3 cells were prelabeled with (65)Zn, it resulted in greater retention of the isotope. In primary hepatocytes, DTPA both reduced the uptake of (65)Zn from the medium and increased efflux from prelabeled cells. To investigate this difference, we studied the effects of DTPA on radioactive zinc flux in the H4IIE (rat hepatoma), MCF-7 (human breast cancer) and Hs578Bst (nontransformed human mammary) cell lines and in rat primary anterior pituitary cells. DTPA reduced the uptake of (65)Zn in all cell lines examined. DTPA increased the retention of (65)Zn in prelabeled H4IIE, MCF-7 and Hs578Bst cells but reduced it in primary pituitary cells. Time course experiments showed that (65)Zn efflux is shut down rapidly by DTPA in transformed cells, whereas the chelator causes greater efflux from primary hepatocytes over the first 6 h. Experiments with (14)C-labeled DTPA confirmed that this chelator does not cross cell membranes, showing that it operates entirely within the medium. Expression of ZnT-1, the efflux transporter, was not affected by DTPA in H4IIE cells. Thus, zinc deprivation enhanced zinc retention in established cell lines but increased efflux from primary cells, perhaps reflecting differing requirements for this mineral.

Development of a compartmental model of zinc kinetics in mice.

To investigate zinc (Zn) kinetics in mice, tracer ((65)Zn) was administered orally to 9-wk-old female mice in the fed state and tracer and Zn concentration were measured in 21 tissues over the following 8 d. Data were analyzed by compartmental modeling using WinSAAM. A published model for Zn kinetics in rats was modified to fit the data from mice and to calculate transfer rates and pool sizes of Zn. Parallel studies were performed in mice lacking genes for metallothionein (MT), MT-I and MT-II (MT-/-), to quantify differences in Zn kinetics in the absence of these proteins in vivo. We confirmed that tracer time course in most tissues was similar in wild-type mice and those lacking MT, except for the pancreas of MT-/-, which retained less tracer. By fitting tissue and intestinal data simultaneously, we found that intestinal tracer could be explained by unabsorbed isotope and loss of Zn from pancreas went through plasma. Differences in pancreatic data in MT-/- were explained by Zn turning over twice as fast in this tissue (4 h) compared with wild type (9 h). These kinetic studies provide parameter values for normal, fed mice that can be used to assess Zn kinetics in abnormal conditions, as demonstrated by the higher turnover of Zn in the pancreas of MT knockout mice.

Biokinetics and dose estimation of 65Zn in the salivary gland and male reproductive organs.

ICRP is revising its recommendations for radiological protection and has added salivary and secretory glands as new target organs. However, little information is available on the distributions of radionuclides in the salivary gland, secretory glands and male reproductive organs. This study deals with the distribution of 65Zn in the salivary gland and male reproductive organs as a function of time after a single intravenous and oral administration. For the study, 64 Wistar strain male rats, eight weeks of age were used. The rats were periodically sacrificed, the liver, kidney, spleen, pancreas, thymus, salivary gland, testis, epididymitis and prostate gland sampled and the radioactivity of these organs measured with an NaI scintillation counter. The relative concentration of 65Zn was highest in the prostate gland. We estimated the radiation dose in humans using rat data for the salivary and secretory glands as well as reproductive organs after intake of 65Zn.

Laboratory analyses of 60Co2+, 65Zn2+ and (55+59)Fe3+ radiocations uptake by Lemna minor.

The living Lemna minor vascular plant and two different sorbents obtained by chemical treatment of this plant were tested to study the removal process of 60Co2+, 65Zn2+ and (55+59)Fe3+ from low radioactive wastewaters. The most effective sorbent was the protonated biomass, indicating the decisive contribution of the complexation process in the assembly of the uptake mechanisms. The uptake performance of the biosorbent obtained from the L. minor can be increased with approximately 20% by treatment with 0.1 N HNO3. Concerning the metabolically active mechanism, it can be notice the slow elimination of 65Zn2+ and the continuously increase of (55+59)Fe3+ uptake degree. The Na2CO3 generated in situ in systems participates to a double exchange reaction with the metallic cations during the uptake. 60Co2+, 65Zn2+ and (55+59)Fe3+ radiocations prefer for coordination N-donor ligands at the expense O-donors ones.

The influence of lithium on biokinetics and biodistribution of 65Zn under different dietary protein regimens in rats.

The present study was designed to evaluate the effect of lithium on the biological half-lives of 65Zn in the rat liver and whole body and also its biodistribution under different dietary protein regimens. To carry out these investigations, each rat after three weeks of different treatments was injected with 1.85 MBq of 65Zn, intraperitoneally (ip) and its radioactivity was recorded in liver as well as in whole body by using gamma ray spectrometer. The radionuclide 65Zn showed two kinetic components indicating its biological half-life: Tb1 the initial fast component and the Tb2 or slow component. Protein deficiency led to a significant elevation of both components in the whole body but not in the liver when compared to the control group. High protein (HP) diet in rats resulted in marked reduction in both components in the liver but not in the whole body. Lithium treatment alone to normal rats caused a significant reduction in the Tb2 but not in the Tb1 component in the whole body as well as in the liver. The administration of lithium normalized the observed increase in both components in the whole body of protein deficient rats. On the contrary, in rats fed with low protein (LP) diet after lithium treatment the Tb(2) component was significantly reduced in the liver. Lithium treatment to HP fed rats, showed a significant decrease in both components in the liver when compared to normal rats: however this decrease was less pronounced in comparison to the HP group that had not been given lithium. Furthermore, one day prior to the end of the treatment period, the rats were injected ip with a tracer dose of 0.37 MBq 65Zn and 24 h later, various organs were excised for 65Zn biodistribution measurements in vitro. Under different dietary protein regimens as well as after administration of lithium the percent uptake values of 65Zn varied in various organs viz: the brain, liver, kidney, small intestine and large intestine as well as in the blood. In conclusion, different protein dietary conditions on co-administration with lithium in the rats seemed to have a dominant role for the retention of 65Zn in the liver the whole body and in other organs.

Effects of Zn pre-exposure on Cd and Zn bioaccumulation and metallothionein levels in two species of marine fish.

Zinc is an essential trace metal but also a potential toxicant to aquatic organisms. In this study, two juvenile marine fish species, the black sea bream Acanthopagrus schlegeli and the grunt Teraponjarbua, were pre-exposed to Zn either from waterborne (0.74-170 microg L-1) or dietary (39-5926 microg g-1) Zn for 1 or 3 weeks. The concentrations of Zn and metallothionein (MT) in the whole body of the black sea bream and in the gills, viscera and carcass of the grunt were then measured during this pre-exposure. Following the pre-exposure, both fish species were then exposed to 109Cd and 65Zn labeled food or water to quantify the dietary assimilation efficiency (AE) and the uptake rate of dissolved Cd and Zn. Zn concentrations in both fish species were enhanced after pre-exposure, but the increases were much less than the increase of ambient Zn pre-exposure concentration. Following Zn pre-exposure, MT concentrations in the viscera and carcass were significantly elevated, whereas the MT levels were not significantly elevated in the gills. Waterborne and dietary Zn exposure enhanced the uptake rates of dissolved Cd and Zn in both fish. The maximum increases of uptake rate constants of dissolved Cd and Zn were up to 1.9-2.8 and 2.1-2.6 times, respectively, in the seabream and grunt. In contrast, dietary assimilation efficiency of Cd and Zn was not significantly enhanced following Zn pre-exposure. A positive linear relationship was found between the uptake rate constants of dissolved metals and Zn or MT concentrations in the fish. The results suggested that Zn pre-exposure increased the potential of metal uptake from ambient water, but had little effect on dietary metal uptake. Furthermore, the Zn body concentration and metal uptake from the dissolved phase were significantly dependent on the fish body size.

Influence of zinc on the status of hepatic trace elements and biokinetics of 65Zn in ethanol treated rats.

Whole body counting studies of 65Zn indicated that the Tb1 (the faster component) was significantly decreased while the slower component (Tb2) was increased significantly following ethanol treatment. Interestingly, following zinc treatment to ethanol treated rats, slower component (Tb2) of 65Zn came back to within normal limits while the faster component (Tb1) got significantly elevated in comparison to ethanol treatment. Percent uptake values of 65Zn were found to be increased in liver, intestine, muscle, brain and kidney, and decreased in bone under alcoholic conditions. Interestingly, the uptake values of 65Zn in all the organs except muscle were reverted back to within normal limits upon zinc supplementation to these ethanol intoxicated animals. A significant decrease in zinc contents was noticed in ethanol treated rats, which, however, were raised to normal levels upon zinc supplementation: Copper levels, on the other hand, were significantly enhanced in both ethanol fed and combined ethanol + zinc treated rats. Calcium levels were significantly decreased in both ethanol and zinc treated rats, which however were further reduced upon zinc supplementation to ethanol fed rats. However, no significant change was observed in the concentrations of sodium and potassium in any of the treatment groups. In conclusion, zinc appears to play a protective role by normalizing the turnover of 65Zn in whole body as well as in its uptake in different organs under alcoholic conditions.

Biokinetics of 65Zn in liver and whole body and its bio-distribution in nickel treated protein deficient rats.

This study was designed to determine the effect of nickel treatment on biological half-lives of 65Zn in whole body and liver as well as on distribution of 65Zn in different organs of protein deficient rats. Nickel sulfate at a dose level of 800mg/l in drinking water was administrated to normal control as well as to protein deficient rats for 8 weeks. A significant increase was found in fast and slow components of biological half lives of 65Zn in whole body and only fast component in liver of protein deficient rats. Interestingly, slow component in whole body and fast component in liver of nickel treated protein deficient rats were not different from normal controls though they were significantly elevated in protein deficient rats. On the other hand, slow component of 65Zn was also not altered in nickel treated protein deficient rats, which however, was significantly decreased in nickel treated rats. Protein deficiency led to a marked elevation in per cent uptake of 65Zn in brain and caused significant depression in liver, kidney and intestine. However, uptake of 65Zn in brain showed a significant depression in nickel treated rats, whereas the uptake was elevated in brain in nickel treated protein deficient rats. In conclusion, protein deficient conditions seem to be playing a dominant role in context with the distribution of 65Zn in different organs when nickel is administered to protein deficient rats. However nickel alone is seen to cause adverse effect on the distribution of 65Zn.

Evaluation of the biological transfer of 32P, 137Cs and 65Zn by fish in the Yenisei River.

The biological transfer of three radionuclides ((32)P, (137)Cs, (65)Zn) by fish in the Yenisei River (Central Siberia, Russia) was evaluated using a radioecological model. The modelling is based on the general ECOMOD methodology, where radionuclide behavior in an aquatic organism is linked with the processes of growth and metabolism, also with the concentrations of stable analogous elements in the organism, its food and the environment. The model was applied to explain the peculiarities of (32)P, (137)Cs and (65)Zn accumulation in different ecological groups of fish, including non-migratory and migratory fish, non-predatory and predatory fish species. The highest activity concentrations in non-migratory fish from the Yenisei River were found for (32)P. The accumulation of (32)P by fish was shown to depend on the fish size (age, weight); however, it did not depend on the trophic status of fish. The modelling approach was developed to evaluate the biological transfer of radionuclides by the migratory fish, which spend the most part of life in the Yenisei delta, inlet or bay, and go upstream the Yenisei River for spawning. The results of the ECOMOD model calculations are in good agreement with available measurement data.

Interference of three weed extracts on uptake of nutrient in three different varieties of paddy through radio tracer techniques.

Interference of three dominant weed extracts viz., Ageratum conyzoides L., Melilotus indica All. and Parthenium hysterophorus L. were examined on seed germination, seedling growth, and nutrient uptake (32P and 65Zn) in three different varieties (PD-10, PD-12 and PB) of paddy (Oryza sativa L.). Among the three different varieties irrespective of weed extracts, PD-10 and PD-12 were resistant and PB was susceptible in terms of seed germination, radicle length and plumule dry weight; and PD-12 and PB were resistant and susceptible, respectively, in terms of plumule length and total seedling dry weight. A. conyzoides caused maximum reduction in seed germination and M. indica in seedling growth in different varieties of paddy. The weed extracts interfered in uptake of both 32P and 65Zn and there was a gradual decrease in uptake of both nutrients with increasing concentration of extracts in both root and shoot. The uptake of 32P and 65Zn was more inhibitory with the extracts of A. conyzoides and M. indica, respectively in different varieties. The inhibition in seed germination, seedling growth and nutrient uptake may be due to the presence of phenolics and other secondary metabolities. The phenolics such as gallic, vanillic, protocatechuic and p-hydroxybenzoic acids were identified from these weed extracts.

Soil-water distribution coefficients and plant transfer factors for (134)Cs, (85)Sr and (65)Zn under field conditions in tropical Australia.

Measurements of soil-to-plant transfer of (134)Cs, (85)Sr and (65)Zn from two tropical red earth soils ('Blain' and 'Tippera') to sorghum and mung crops have been undertaken in the north of Australia. The aim of the study was to identify factors that control bioaccumulation of these radionuclides in tropical regions, for which few previous data are available. Batch sorption experiments were conducted to determine the distribution coefficient (K(d)) of the selected radionuclides at pH values similar to natural pH values, which ranged from about 5.5 to 6.7. In addition, K(d) values were obtained at one pH unit above and below the soil-water equilibrium pH values to determine the effect of pH. The adsorption of Cs showed no pH dependence, but the K(d) values for the Tippera soils (2300-4100 ml/g) exceeded those for the Blain soils (800-1200 ml/g) at equilibrium pH. This was related to the greater clay content of the Tippera soil. Both Sr and Zn were more strongly adsorbed at higher pH values, but the K(d) values showed less dependence on the soil type. Strontium K(d)s were 30-60 ml/g whilst Zn ranged from 160 to 1630 ml/g for the two soils at equilibrium pH. With the possible exception of Sr, there was no evidence for downward movement of radionuclides through the soils during the course of the growing season. There was some evidence of surface movement of labelled soil particles. Soil-to-plant transfer factors varied slightly between the soils. The average results for sorghum were 0.1-0.3 g/g for Cs, 0.4-0.8 g/g for Sr and 18-26 g/g for Zn (dry weight) with the initial values relating to Blain and the following values to Tippera. Similar values were observed for the mung bean samples. The transfer factors for Cs and Sr were not substantially different from the typical values observed in temperate studies. However, Zn transfer factors for plants grown on both these tropical soils were greater than for soils in temperate climates (by more than an order of magnitude). This may be related to trace nutrient deficiency and/or the growth of fungal populations in these soils. The results indicate that transfer factors depend on climatic region together with soil type and chemistry and underline the value of specific bioaccumulation data for radionuclides in tropical soils.