Cadmium, copper, and lead accumulation and bioconcentration in the vegetative and reproductive organs of Raphanus sativus: implications for plant performance and pollination.

Several studies have found high levels of cadmium (Cd), copper (Cu), and lead (Pb) in honey bee hives located near urbanized or industrial areas. Insect herbivores and pollinators may come in contact with environmental contaminants in the leaves and flowers they forage upon in these areas. Our study quantified which of these metals are accumulated in the tissues of a common weedy plant that can serve as a route of exposure for insects. We grew Raphanus sativus (crop radish) in semi-hydroponic sand culture in the greenhouse. Plants were irrigated with nutrient solutions containing Cd, Cu, or Pb at four concentrations (control, low, medium, high). Plant performance, floral traits, and metal accumulation were measured in various vegetative and reproductive plant organs. Floral traits and flower number were unaffected by all metal treatments. Copper accumulated at the highest concentrations in flowers compared to the other two metals. Copper and Cd had the highest translocation indices, as well as higher bioconcentration factors compared to Pb, which was mostly immobile in the plant. Copper posed the highest risk due to its high mobility within the plant. In particular, accumulation of metals in leaves and flowers suggests that herbivores and pollinators visiting and foraging on these tissues may be exposed to these potentially toxic compounds.

Effect of transpiration on plant accumulation and translocation of PPCP/EDCs.

The reuse of treated wastewater for agricultural irrigation in arid and hot climates where plant transpiration is high may affect plant accumulation of pharmaceutical and personal care products (PPCPs) and endocrine disrupting chemicals (EDCs). In this study, carrot, lettuce, and tomato plants were grown in solution containing 16 PPCP/EDCs in either a cool-humid or a warm-dry environment. Leaf bioconcentration factors (BCF) were positively correlated with transpiration for chemical groups of different ionized states (p < 0.05). However, root BCFs were correlated with transpiration only for neutral PPCP/EDCs (p < 0.05). Neutral and cationic PPCP/EDCs showed similar accumulation, while anionic PPCP/EDCs had significantly higher accumulation in roots and significantly lower accumulation in leaves (p < 0.05). Results show that plant transpiration may play a significant role in the uptake and translocation of PPCP/EDCs, which may have a pronounced effect in arid and hot climates where irrigation with treated wastewater is common.

Impact of selenium on mortality, bioaccumulation and feeding deterrence in the invasive Argentine ant, Linepithema humile (Hymenoptera: Formicidae).

Ants are known for the important roles they play in processes contributing to ecosystem functioning in many habitats. However, pollutants can impact the ecosystem services provided by ants. The Argentine ant, an invasive species in North America, was investigated for the potential impact selenium (Se) may have on ants residing within a contaminated habitat. Mortality tests were conducted using worker ants fed an artificial nectar source containing 1-of-4 environmentally common Se compounds (forms): seleno-l-methionine, methylselenocysteine, selenate or selenite. Accumulation of Se in ant bodies at the end of two weeks was quantified with the use of hydride generation atomic absorption spectroscopy. Lastly, we conducted choice tests using dyes to determine whether ants might avoid a carbohydrate diet containing Se by providing them a choice between sucrose with or without Se. Choice tests also tested the responses of ants to selenium when provided in different background sucrose concentrations. The results of this study indicated that form and quantity of Se, as well as time of exposure, impact mortality in Argentine ant workers. Methylselenocysteine and selenate were found to be the most toxic among the 4 chemical forms when presented in sucrose solutions, whereas seleno-l-methionine and selenite caused greater Se body burdens. Furthermore, choice tests showed that ants did not prefer control sucrose solution to sucrose treated with Se regardless of the background sucrose concentration. These findings serve as first look into the possible detrimental impacts these contaminants may pose for ants that frequent sugary nectar sources.

Effects of selenium on development, survival, and accumulation in the honeybee (Apis mellifera L.).

Apis mellifera L. (Hymenoptera: Apidae) is an important agricultural pollinator in the United States and throughout the world. In areas of selenium (Se) contamination, honeybees may be at risk because of the biotransfer of Se from plant products such as nectar and pollen. Several forms of Se can occur in accumulating plants. In the present study, the toxicity of 4 compounds (selenate, selenite, methylselenocysteine, and selenocystine) to honeybee adult foragers and larvae was assessed using dose-response bioassays. Inorganic forms were more toxic than organic forms for both larvae (lethal concentration [LC50] selenate = 0.72 mg L(-1) , LC50 selenite = 1.0 mg L(-1) , LC50 methylselenocysteine = 4.7 mg L(-1) , LC50 selenocystine = 4.4 mg L(-1) ) and foragers (LC50 selenate = 58 mg L(-1) , LC50 selenite = 58 mg L(-1) , LC50 methylselenocysteine = 161 mg L(-1) , LC50 selenocystine = 148 mg L(-1) ). Inorganic forms of Se caused rapid mortality, and organic forms had sublethal effects on development. Larvae accumulated substantial amounts of Se only at the highest doses, whereas foragers accumulated large quantities at all doses. The present study documented very low larval LC50 values for Se; even modest transfer to brood will likely cause increased development times and mortality. The toxicities of the various forms of Se to honeybee larvae and foragers are discussed in comparison with other insect herbivores and detritivores.

Trophic Transfer of Arsenic from an Aquatic Insect to Terrestrial Insect Predators.

The movement of energy and nutrients from aquatic to terrestrial ecosystems can be substantial, and emergent aquatic insects can serve as biovectors not only for nutrients, but also for contaminants present in the aquatic environment. The terrestrial predators Tenodera aridifolia sinensis (Mantodea: Mantidae) and Tidarren haemorrhoidale (Araneae: Theridiidae) and the aquatic predator Buenoa scimitra (Hemiptera: Notonectidae) were chosen to evaluate the efficacy of arsenic transfer between aquatic and terrestrial environments. Culex tarsalis larvae were reared in either control water or water containing 1000 µg l(-1) arsenic. Adults that emerged from the control and arsenic treatments were fed to the terrestrial predators, and fourth instar larvae were fed to the aquatic predator reared in control or arsenic contaminated water. Tenodera a. sinensis fed arsenic-treated Cx. tarsalis accumulated 658±130 ng g(-1) of arsenic. There was no significant difference between control and arsenic-fed T. haemorrhoidale (range 142-290 ng g(-1)). Buenoa scimitra accumulated 5120±406 ng g(-1) of arsenic when exposed to arsenic-fed Cx. tarsalis and reared in water containing 1000 µg l(-1) arsenic. There was no significant difference between controls or arsenic-fed B. scimitra that were not exposed to water-borne arsenic, indicating that for this species environmental exposure was more important in accumulation than strictly dietary arsenic. These results indicate that transfer to terrestrial predators may play an important role in arsenic cycling, which would be particularly true during periods of mass emergence of potential insect biovectors. Trophic transfer within the aquatic environment may still occur with secondary predation, or in predators with different feeding strategies.

Effects of selenium accumulation on phytotoxicity, herbivory, and pollination ecology in radish (Raphanus sativus L.).

Selenium (Se) has contaminated areas in the western USA where pollination is critical to the functioning of both agricultural and natural ecosystems, yet we know little about how Se can impact pollinators. In a two-year semi-field study, the weedy plant Raphanus sativus (radish) was exposed to three selenate treatments and two pollination treatments to evaluate the effects on pollinator-plant interactions. Honey bee (Apis mellifera L.) pollinators were observed to readily forage on R. sativus for both pollen and nectar despite high floral Se concentrations. Se treatment increased both seed abortion (14%) and decreased plant biomass (8-9%). Herbivory by birds and aphids was reduced on Se-treated plants, indicating a potential reproductive advantage for the plant. Our study sheds light on how pollutants such as Se can impact the pollination ecology of a plant that accumulates even moderate amounts of Se.

Self-control in postsecondary settings: students' perceptions of ADHD college coaching.

OBJECTIVE: The objective of this study was to identify undergraduates' perceptions of the impact of ADHD coaching on their academic success and broader life functioning. METHOD: One-on-one interviews were conducted with 19 students on 10 different U.S. campuses who comprised a purposive sample of gender, cumulative grade point average, and self-regulation skills variables as measured by the learning and study strategies inventory. Interview transcripts were coded using NVivo 8 software, and emergent themes were triangulated with students' descriptions of personal artifacts that symbolized coaching's influence on their lives. RESULTS: Students reported that ADHD coaching helped them become more self-regulated, which led to positive academic experiences and outcomes. Students described ADHD coaching as a unique service that helped them develop more productive beliefs, experience more positive feelings, and engage in more self-regulated behaviors. CONCLUSION: ADHD coaching helped participants enhance their self-control as they responded to the multifaceted demands of undergraduate life.

Survival, reproduction, and arsenic body burdens in Chironomus riparius exposed to arsenate and phosphate.

Despite the increasing awareness of arsenic (As) contamination in surface waters worldwide, little is known about how As alone and in the presence of other chemicals affects aquatic insects. Larvae of Chironomus riparius were exposed in a laboratory investigation to factorial combinations of 0, 0.13, 2.0, 5.3, and 13 µmol As l(-1) and 0, 0.15, and 15 µmol PO(4) l(-1) throughout development from first instar to pupal emergence. The time between male and female emergence increased from 1.8±0.17 days to 2.9±0.34 days with exposure at higher As levels. The highest As exposure also decreased the number of eggs per egg mass, which may affect population maintenance. For these parameters, there was no effect from PO(4), and no interaction between As and PO(4). Total As determination of larval and adult tissues was conducted using Hydride Generated Atomic Absorption Spectroscopy (HGAAS) and revealed concentrations ranging from 2.48±0.363 to 30.5±0.473 µg/g and 1.03±0.286 to 8.97±0.662 µg/g, respectively, indicating elimination of approximately 72% of total As body burdens between the fourth instar and adult stages. There was no effect of PO(4), indicating PO(4) does not alter uptake of As in C. riparius. The potential for movement of As to terrestrial systems exists, though trophic transfer may be more likely during the aquatic larval stage.

Effects of pollutant accumulation by the invasive weed saltcedar (Tamarix ramosissima) on the biological control agent Diorhabda elongata (Coleoptera: Chrysomelidae).

Hydroponic greenhouse studies were used to investigate the effect of four anthropogenic pollutants (perchlorate (ClO4(-)), selenium (Se), manganese (Mn), and hexavalent chromium (Cr (VI))) on the biological control agent Diorhabda elongata Brullé. Contaminant concentrations were quantified for experimental Tamarix ramosissima Ledab. plants and D. elongata beetles. Growth of larvae was significantly reduced by Se contamination, but was not affected by the presence of perchlorate, Mn, or Cr (VI). All of the contaminants were transferred from plants to D. elongata beetles. Only Cr (VI) was accumulated at greater levels in beetles than in their food. Because T. ramosissima grows in disturbed areas, acquires salts readily, and utilizes groundwater, this plant is likely to accumulate anthropogenic pollutants in contaminated areas. This study is one of the first to investigate the potential of an anthropogenic pollutant to influence a weed biological control system.

Glucagon is absorbed from the rectum but does not hasten recovery from hypoglycaemia in patients with type 1 diabetes.

AIMS: A failure to secrete glucagon during hypoglycaemia is near universal in patients with type 1 diabetes 5 years after disease onset and may contribute to delayed counter-regulation during hypoglycaemia. Rectal glucagon delivery may assist glucose recovery following insulin-induced hypoglycaemia in such patients and has not been previously studied. METHODS: Six male patients (age 21-38 years) with type 1 diabetes (median duration 10 years) without microvascular complications, were studied supine after an overnight fast on two separate occasions at least 14 days apart. After omission of their usual morning insulin and 45 min rest, hypoglycaemia was induced by an intravenous insulin infusion which was terminated when capillary glucose concentration reached 2.5 mmol l(-1). Subjects were randomized to insert a rectal suppository containing 100 mg indomethacin alone (placebo) or 100 mg indomethacin plus 1 mg glucagon at the hypoglycaemic reaction. Serial measurements were made for 120 min. RESULTS: In the two groups, mean (SD) plasma glucose concentrations fell to a similar nadir of 1.8 (0.7) mmol l(-1) (placebo) and 2.1 (1.2) mmol l(-1) (glucagon). Peak plasma glucagon following hypoglycaemia was higher in the glucagon group; 176 (32) ng l(-1)vs. 99 (22) ng l(-1) after placebo (P = 0.006). However, the glucose recovery rate over 120 min after hypoglycaemia did not differ significantly. CONCLUSIONS: Our results provide evidence for the absorption of glucagon from the rectum. They also indicate that 1 mg does not constitute a useful mode of therapy to hasten recovery from hypoglycaemia in patients with type 1 diabetes.

Perchlorate in groundwater: a synoptic survey of "pristine" sites in the coterminous United States.

Perchlorate is widely used as an oxidant in solid rocket propellants and energetic applications, and it has frequently been detected in groundwaters at concentrations relevant to human health. The possibility of naturally occurring perchlorate has only recently received significant attention. Relying primarily on domestic, agricultural, and recreational wells, we utilized a network of volunteers to help collect 326 groundwater samples from across the coterminous United States. Care was taken to avoid known, USEPA-documented sites of perchlorate use or release, as well as perchlorate contamination due to disinfection using hypochlorite. Using IC-ESI-MS and a Cl18O4- internal standard, we achieved a method detection limit (MDL) of 40 ng/L perchlorate and a minimum reporting level (MRL) of 120 ng/L. Of the 326 samples, 147 (45%) were below the MDL, while 42 (13%) were between the MDL and the MRL. Of the 137 samples that could be quantified, most (109) contained < 1000 ng/L perchlorate; the remaining 28 samples contained from 1000 to 10400 ng/L. Our results support the notion that perchlorate occurs naturally in many groundwaters, but the unusually high concentrations (> 10000 ng/L) previously reported for the west-central Texas area appear to be anomalous. Perchlorate concentrations were positively correlated with nitrate levels (P < 0.001) but not with chloride concentrations. Opportunities exist for follow-up studies of perchlorate's origins using isotope forensics and for further elucidation of the role of atmospheric processes in the formation or transport of perchlorate.

Is perchlorate metabolized or re-translocated within lettuce leaves? A stable-isotope approach.

Perchlorate is an environmental contaminant that is found in drinking water and a variety of foodstuffs, but many questions regarding its uptake, transport, and persistence in higher plants remain unanswered. In a series of hydroponic experiments, a stable-isotope tracer of perchlorate (95% 37ClO4(-)) was utilized to determine the extent of in vivo metabolism and of phloem re-translocation of perchlorate at low (i.e., nmol/kg of fresh weight (FW)) concentrations in lettuce. Chlorate and chlorite metabolites were not detected in lettuce leaves at detection limits of 13.1 and 291 nmol/kg FW, respectively, and chloride isotopic signatures were not substantially different from natural chloride. Perchlorate exhibited no significant movement from older leaves into new leaves, nor to roots. Stable isotopes proved useful in assessing perchlorate metabolism and re-translocation within lettuce at nmol/kg levels. The absence of any metabolism or re-translocation indicates that perchlorate is relatively persistent within leafy produce, and that the primary mode of transport of perchlorate is through the xylem of higher plants.

Cardinal interpolation.

A Bayesian probability density for an interpolating function is developed, and its desirable properties and practical potential are demonstrated. This density has an often needed but previously unachieved property, here called cardinal interpolation, which ensures extrapolation to the density of the least squares linear model. In particular, the mean of the cardinal interpolation density is a smooth function that intersects given (x, y) points and which extrapolates to their least squares line, and the variance of this density is a smooth function that is zero at the point x values, that increases with distance from the nearest point x value, and that extrapolates to the well-known quadratic variance function for the least squares line. The new cardinal interpolation density is developed for Gaussian radial basis interpolators using fully Bayesian methods that optimize interpolator smoothness. This optimization determines the basis function widths and yields an interpolating density that is non-Gaussian except for large magnitude x and which is therefore not the outcome of a Gaussian process. Further new development shows that the salient property of extrapolation to the density of the least squares linear model can be achieved for more general approximating (not just interpolating) functions.

Effects of genotype and transpiration rate on the uptake and accumulation of perchlorate (ClO4-) in lettuce.

Although evidence of perchlorate accumulation in plants exists, there is a scarcity of information concerning the key factors and mechanisms involved. To ascertain whether genotypic variation in perchlorate accumulation occurs within lettuce, hydroponic plant uptake experiments were conducted with five types of lettuce (Lactuca sativa L.), which were grown to market size atthree perchlorate (ClO4-) concentrations (1, 5, or 10 microg/L). Perchlorate accumulated in the leafy tissues to varying amounts, ranging from 4 to 192 microg/kg fresh weight (FW), and the ranking of perchlorate accumulation was crisphead > butter head > romaine > red leaf > green leaf. The effect of transpiration rate on perchlorate accumulation was further examined using crisphead, butter head, and green leaf lettuce. By growing lettuce in controlled-environment chambers with two climatic regimes, "cloudy, humid, cool" (80% RH, 18/15 degrees C, 250 micromol/m2s photosynthetic photon flux density (PPFD)) and "sunny, dry, warm" (approximately 50% RH, 28/18 degrees C, 500 micromol/m2s PPFD), up to 2.7-fold differences in transpiration rates were achieved. Across all three genotypes, the plants that transpired more water accumulated more perchlorate on a whole-head basis; however, the effect of transpiration rate on perchlorate accumulation was not as great as expected. Despite 2.0-2.7-fold differences in transpiration rate, there were only 1.2-2.0-fold differences in perchlorate accumulation. In addition to whole-head analysis, plants were sectioned into inner, middle, and outer leaves and processed separately. Overall, the ranking of perchlorate accumulation was outer leaves > middle leaves > inner leaves. Transpiration rate has a clear effect on perchlorate accumulation in lettuce, but other factors are influential and deserve exploration.

Determination of low levels of perchlorate in lettuce and spinach using ion chromatography-electrospray ionization mass spectrometry (IC-ESI-MS).

A sample preparation method was developed to quantify environmentally relevant (low micrograms per liter) concentrations of perchlorate (ClO4(-)) in leafy vegetables using IC-ESI-MS. Lettuce and spinach were macerated, centrifuged, and filtered, and the aqueous extracts were rendered water-clear using a one-step solid-phase extraction method. Total time for extraction and sample preparation was 6 h. Ion suppression was demonstrated and was likely due to unknown organics still present in the extract solution after cleanup. However, this interference was readily eliminated using a Cl(18)O4(-) internal standard at 1 microg/L in all standards and samples. Hydroponically grown perchlorate-free butterhead lettuce was spiked to either 10.3 or 37.7 microg/kg of fresh weight (FW), and recoveries were between 91 and 98% and between 93 and 101%, respectively. Five types of lettuce and spinach from a local grocery store were then analyzed; they contained from 0.6 to 6.4 microg/kg of FW. Spike recoveries using the store-bought samples ranged from 89 to 100%. The method detection limit for perchlorate in plant extracts is 40 ng/L, and the corresponding minimum reporting limit is 200 ng/L or 0.8 microg/kg of FW.

Organic acid secretion as a mechanism of aluminium resistance: a model incorporating the root cortex, epidermis, and the external unstirred layer.

The resistance of some plants to Al (aluminium or aluminum) has been attributed to the secretion of Al(3+)-binding organic acid (OA) anions from the Al-sensitive root tips. Evidence for the 'OA secretion hypothesis' of resistance is substantial, but the mode of action remains unknown because the OA secretion appears to be too small to reduce adequately the activity of Al(3+) at the root surface. In this study a mechanism for the reduction of Al(3+) at the root surface and just beneath the epidermis by complexation with secreted OA(2-) is considered. According to our computations, Al(3+) activity is insufficiently reduced at the surface of the root tips to account for the Al resistance of Triticum aestivum L. cv. Atlas 66, a malate-secreting wheat. Experimental treatments to decrease the thickness of the unstirred layer (increased aeration and removal of root-tip mucilage) failed to enhance sensitivity to Al(3+). On the basis of additional modelling, the observed spatial distribution of Al in roots, and the anatomical responses to Al, it is proposed that the epidermis is an essential component of the diffusion pathway for both OA and Al. We suggest that Al(3+) in the cortex must be reduced to small concentrations in order substantially to alleviate the inhibition of root elongation and so that the outer surface of the epidermis can tolerate relatively large concentrations of Al(3+). If OA secretion is required for reducing Al(3+) mainly beneath the root surface, rather than in the rhizosphere, then the metabolic cost to plants will be greatly reduced.

Critical evaluation of the ability of sequential extraction procedures to quantify discrete forms of selenium in sediments and soils.

Sequential extraction procedures (SEPs) have been widely used to characterize the mobility, bioavailibility, and potential toxicity of trace elements in soils and sediments. Although oft-criticized, these methods may perform best with redox-labile elements (As, Hg, Se) for which more discrete biogeochemical phases may arise from variations in oxidation number. We critically evaluated two published SEPs for Se for their specificity and precision by applying them to four discrete components in an inert silica matrix: soluble Se(VI) (selenate), Se(IV) (selenite) adsorbed onto goethite, elemental Se, and a metal selenide (FeSe; achavalite). These were extracted both individually and in a mixed model sediment. The more selective of the two procedures was modified to further improve its selectivity (SEP 2M). Both SEP 1 and SEP 2M quantitatively recovered soluble selenate but yielded incomplete recoveries of adsorbed selenite (64% and 81%, respectively). SEP 1 utilizes 0.1 M K2S2O8 to target "organically associated" Se, but this extractant also solubilized most of the elemental (64%) and iron selenide (91%) components of the model sediment. In SEP 2M, the Na2SO3 used in step III is effective in extracting elemental Se but also extracted 17% of the Se from the iron selenide, such that the elemental fraction would be overestimated should both forms coexist. Application of SEP 2M to eight wetland sediments further suggested that the Na2SO3 in step III extracts some organically associated Se, so a NaOH extraction was inserted beforehand to yield a further modification, SEP 2OH. Results using this five-step procedure suggested that the four-step SEP 2M could overestimate elemental Se by as much as 43% due to solubilization of organic Se. Although still imperfect in its selectivity, SEP 20H may be the most suitable procedure for routine, accurate fractionation of Se in soils and sediments. However, the strong oxidant (NaOCl) used in the final step cannot distinguish between refractory organic forms of Se and pyritic Se that might form under sulfur-reducing conditions.

Soil selenium uptake and root system development in plant taxa differing in Se-accumulating capability.

• Phytoremediation of Se-contaminated soils and sediments may be more feasible if accumulating taxa are identified that can extract the more refractory forms of Se. • In a glasshouse study, the capacity of six plant genotypes to take up labile and nonlabile soil Se was evaluated by amending five high-Se soils (2-21 mg kg-1 total Se) with carrier-free 75 Se, and cropping them with Astragalus bisulcatus, Astragalus canadensis, Brassica juncea, Sporobolus airoides, and two ecotypes of Stanleya pinnata. • The biologically labile pool of soil Se (L-value) was computed from the isotopic signature of the harvested shoots, and ranged from 2 to 37% of the total soil Se. The chemically labile pool (E-value) was determined via extraction in 0.1 m KCl, and ranged from 4 to 73% of total soil Se. None of the plants tested yielded L-values that were consistently greater than the E-values, suggesting that all plants, including Se hyperaccumulators, access the same labile pools of Se. • Root-growth experiments in rhizoboxes using Se-enriched soil were also performed. Although our observations were not as striking as those made for the Zn(Cd)-accumulator Thlaspi caerulescens, the tendency for roots of some Se-accumulators to proliferate in soil where Se is present deserves further investigation.

Vertical distribution of ozone and nitric acid vapor on the Mammoth Mountain, eastern Sierra Nevada, California.

In August and September 1999 and 2000, concentrations of ozone (O3) and nitric acid vapor (HNO3) were monitored at an elevation gradient (2184-3325 m) on the Mammoth Mountain, eastern Sierra Nevada, California. Passive samplers were used for monitoring exposure to tropospheric O3 and HNO3 vapor. The 2-week average O3 concentrations ranged between 45 and 72 ppb, while HNO3 concentrations ranged between 0.06 and 0.52 microg/m3. Similar ranges of O3 and HNO3 were determined for 2 years of the study. No clear effects of elevation on concentrations of the two pollutants were detected. Concentrations of HNO3 were low and at the background levels expected for the eastern Sierra Nevada, while the measured concentrations of O3 were elevated. High concentrations of ozone in the study area were confirmed with an active UV absorption O3 monitor placed at the Mammoth Mountain Peak (September 5-14, 2000, average 24-h concentration of 56 ppb).