Control of Globodera pallida Using Brassica juncea Seed Meal Extract and the Trap Crop Solanum sisymbriifolium.

Globodera pallida, the pale cyst nematode, is a regulated potato pest which is economically detrimental. Restrictions on use of the soil fumigant methyl bromide and lack of resistant russet type varieties for U.S. markets have led to investigations of alternative strategies to control this pest. The efficacy of Brassica juncea seed meal extract (SME; 0, 0.14, 0.28, 0.56, 1.12, and 2.24 t/ha) was studied, either alone or in combination with the trap crop Solanum sisymbriifolium under greenhouse and field conditions. The impact of the application of SME pre- or postplanting of S. sisymbriifolium was also determined. S. sisymbriifolium only induced hatch of G. pallida and significantly fewer (up to 57 and 55% in pre- and postplant experiments, respectively) encysted eggs remained at termination of the experiment compared with the untreated control. However, when SME was applied preplant, the encysted eggs remained unchanged, which may indicate that SME inhibited egg hatch in the presence of S. sisymbriifolium. When applied individually, S. sisymbriifolium in all experiments, or SME at all rates tested in the greenhouse or 0.56 t/ha or higher rates of SME in the field, significantly reduced the viability, hatch, and reproduction of G. pallida. Combined treatment with S. sisymbriifolium and SME at lower rates (0.14 t/ha for preplant or 0.56 t/ha or less for the greenhouse postplant experiment) reduced G. pallida egg hatch further than each strategy alone. In the field, a combination of S. sisymbriifolium and SME at 1.12 t/ha or less reduced G. pallida more effectively than SME alone. SME alone applied at higher rates (0.56 and 1.12 t/ha) in preplant greenhouse trials, whether or not combined with S. sisymbriifolium, eliminated G. pallida reproduction. Under field conditions, SME applied at a rate of 1.12 t/ha highly reduced G. pallida reproduction compared with the untreated control by 97 and 61% in 2019 and 2020, respectively. Furthermore, reproduction of G. pallida was eliminated when SME was combined with S. sisymbriifolium. Our results indicated that a combination of SME and S. sisymbriifolium reduces the amount of SME needed to control G. pallida and further decreases the potential reserve of the viable population remaining after individual treatment with each strategy.

Dairy manure as a potential source of crop nutrients and environmental contaminants.

Although animal manure is applied to agricultural fields for its nutrient value, it may also contain potential contaminants. To determine the variability in such contaminants as well as in valuable nutrients, nine uncomposted manure samples from Idaho dairies collected during 2.5 years were analyzed for macro- and micro-nutrients, hormones, phytoestrogens, antibiotics, veterinary drugs, antibiotic resistance genes, and genetic elements involved in the spread of antibiotic resistance. Total N ranged from 6.8 to 30.7 (C:N of 10 to 21), P from 2.4 to 9.0, and K from 10.2 to 47.7 g/kg manure. Zn (103 - 348 mg/kg) was more abundant than Cu (56 - 127 mg/kg) in all samples. Phytoestrogens were the most prevalent contaminants detected, with concentrations fluctuating over time, reflecting animal diets. This is the first study to document the presence of flunixin, a non-steroidal anti-inflammatory drug, in solid stacked manure from regular dairy operations. Monensin was the most frequently detected antibiotic. Progesterones and sulfonamides were regularly detected. We also investigated the relative abundance of several types of plasmids involved in the spread of antibiotic resistance in clinical settings. Plasmids belonging to the IncI, IncP, and IncQ1 incompatibility groups were found in almost all manure samples. IncQ1 plasmids, class 1 integrons, and sulfonamide resistance genes were the most widespread and abundant genetic element surveyed, emphasizing their potential role in the spread of antibiotic resistance. The benefits associated with amending agricultural soils with dairy manure must be carefully weighed against the potential negative consequences of any manure contaminants.

Fate of the nonsteroidal, anti-inflammatory veterinary drug flunixin in agricultural soils and dairy manure.

A large percentage of flunixin, a nonsteroidal anti-inflammatory drug widely used for treating livestock, is excreted in intact form and thus potentially available for environmental transport. As the fate of flunixin in the environment is unknown, our objective was to quantify sorption, desorption, and transformation in five agricultural soils and manure using batch equilibrium methods. Concentrations of flunixin and degradation products were determined by high performance liquid chromatography time of flight mass spectrometry. For all studied soils, sorption of flunixin exhibited linear character, with both linear and Freundlich models providing adequate fit. Linear sorption coefficients varied from 8 to 112 L kg-1. The strongest Pearson correlations with sorption coefficients were for clay content (r = 0.8693), total nitrogen (r = 0.7998), and organic carbon (r = 0.6291). Desorption of the reversibly bound fraction (3-10% of total sorbed flunixin) from all five studied soils exhibited non-hysteretic character suggesting low affinity of this fraction of flunixin to soil. Flunixin degradation in soils was relatively slow, exhibiting half-lives of 39-203 days, thus providing time for off-site transport and environmental contamination. The biological impacts of flunixin at environmentally relevant concentrations must be determined given its environmental behavior and extensive use as a nonsteroidal anti-inflammatory drug in livestock. Graphical abstract.

Feeding intensity of insect herbivores is associated more closely with key metabolite profiles than phylogenetic relatedness of their potential hosts.

Determinants of the host ranges of insect herbivores are important from an evolutionary perspective and also have implications for applications such as biological control. Although insect herbivore host ranges typically are phylogenetically constrained, herbivore preference and performance ultimately are determined by plant traits, including plant secondary metabolites. Where such traits are phylogenetically labile, insect hervivore host ranges are expected to be phylogenetically disjunct, reflecting phenotypic similarities rather than genetic relatedness among potential hosts. We tested this hypothesis in the laboratory with a Brassicaceae-specialized weevil, Ceutorhynchus cardariae Korotyaev (Coleoptera: Curculionidae), on 13 test plant species differing in their suitability as hosts for the weevil. We compared the associations between feeding by C. cardariae and either phenotypic similarity (secondary chemistry-glucosinolate profile) or genetic similarity (sequence of the chloroplast gene ndhF) using two methods-simple correlations or strengths of association between feeding by each species, and dendrograms based on either glucosinolates or ndhF sequence (i.e., a phylogram). For comparison, we performed a similar test with the oligophagous Plutella xylostella (L.) (Lepidoptera: Plutellidae) using the same plant species. We found using either method that phenotypic similarity was more strongly associated with feeding intensity by C. cardariae than genetic similarity. In contrast, neither genetic nor phenotypic similarity was significantly associated with feeding intensity on the test species by P. xylostella. The result indicates that phenotypic traits can be more reliable indicators of the feeding preference of a specialist than phylogenetic relatedness of its potential hosts. This has implications for the evolution and maintenance of host ranges and host specialization in phytophagous insects. It also has implications for identifying plant species at risk of nontarget attack by potential weed biological control agents and hence the approach to prerelease testing.

Association between extracted copper and dissolved organic matter in dairy-manure amended soils.

Dairy manure often has elevated concentrations of copper (Cu) that when applied to soil may create toxicity risks to seedlings and soil microbes. Manure application also increases dissolved organic matter (DOM) in soil solution. We hypothesize that high rates of dairy manure amendment over several years will cause increased DOM in the soil that complexes Cu, increasing its mobility. To test this hypothesis, this study investigated water soluble Cu concentrations and dissolved organic carbon (DOC) in soil samples from 3 years of manure-amended soils. Samples were collected at two depths over the first 3 years of a long-term manure-amendment field trial. DOC, Cu, Fe, and P concentrations were measured in water extracts from the samples. Ultraviolet/visible (UV/Vis) spectra were used to assess the DOC characteristics. After 3 years of manure application, extractable Cu concentration was approximately four times greater in the surface and two times greater in subsurface samples of manure-amended soils as compared to non-amended control soils and traditional mineral fertilizer-amended soils. The extractable Cu concentration was greatest in plots that had the highest manure amendment rates (35 t ha-1 and 52 t ha-1, dry weight). The UV/Vis parameters SUVA254 and E2/E3 correlated with Cu concentration in the extracts (p < 0.05), suggesting that DOC characteristics are important in Cu-binding. The molecular characteristics of the DOC in the subsurface after 3 years of manure amendment were distinct from the DOC in the control plot, suggesting that manure amendment creates mobile DOC that may facilitate Cu mobilization through soil. The 10-fold increase in extractable Cu concentration after only 3 years of manure application indicates that repeated applications of the dairy manure sources used in this study at rates of 35 t/ha or greater may create risks for Cu toxicity and leaching of Cu into ground and surface waters.

Transport of Potential Manure Hormone and Pharmaceutical Contaminants through Intact Soil Columns.

Although adding manure to agricultural soils is a commonly practiced disposal method and a means to enhance soil productivity, potential environmental contamination by any associated chemicals of emerging concern (CECs) such as hormones and pharmaceuticals is not well understood. Our objective was to provide field-relevant predictions of soil transport and attenuation of 19 potential manure CECs using undisturbed soil columns irrigated under unsaturated conditions. The CEC concentrations in leached water were monitored for 13 wk using high performance liquid chromatography-time of flight-mass spectrometry (HPLC-TOF-MS), after which time soil in the cores was removed and sampled for extractable CECs. Compounds quantified in column leachate included all four of the added sulfonamide antibiotics and the nonsteroidal, anti-inflammatory drug flunixin. Only trace amounts of several of the seven hormones, five remaining antibiotics, and two antimicrobials leached from the columns from exogenous soil additions. Soil residues of all 19 compounds were detected, with highest extractable amounts for 17α-hydroxyprogesterone > triclosan (antimicrobial) > flunixin > oxytetracycline. Those CECs with the highest recoveries as calculated by summing leached and extractable amounts were flunixin (14.5%), 17α-hydroxyprogesterone (5.3%), triclosan (4.6%), and sulfadimethoxine (4.8%). Manure management to prevent CEC contamination should consider the potential environmental problems caused by negatively charged compounds with the greatest mobility (flunixin and sulfadimethoxine) and those that have long residence times in soil (triclosan, 17α-hydroxyprogesterone, flunixin, and oxytetracycline). Flunixin is particularly important given its mobility and long residence time in soil.

Pressurized liquid extraction of six tetracyclines from agricultural soils.

Veterinary antibiotics used in agriculture can be introduced into the environment through land application of animal manure, accumulating in soils and groundwaters and posing a significant risk to human health and animal well-being. As the analysis of tetracyclines in soil is challenging due to their strong interaction with soil minerals and organic carbon, the objective of this study was to develop a reliable and reproducible method for quantitative analysis of chlortetracycline and oxytetracycline, and their respective metabolites in soils. A method based on pressurized liquid extraction (PLE) with in-cell clean-up was developed for the extraction of chlortetracycline and oxytetracycline and four likely metabolites from a set of four soils. Optimized conditions included a cell size of 22 mL, soil loading of 5 g, pH of 8.0, methanol:water ratio of 3:1, 50 °C, and two cycles. Soil extracts were analysed by high-performance liquid chromatography (HPLC) coupled with ion trap mass spectrometry (MS). Recoveries of seven tetracyclines from soil ranged from 41% to 110%. The limits of detection for tetracyclines were 0.08-0.3 µg g-1 soil, and intra- and inter-day variation ranged from 0.12-0.34%. The proposed PLE method is suitable for quantification of tetracyclines in agricultural soils at typical concentrations expected in contaminated environments.

The Influence of Microneedles on the Percutaneous Penetration of Selected Antihypertensive Agents: Diltiazem Hydrochloride and Perindopril Erbumine.

BACKGROUND: It is well documented in the scientific literature that high blood pressure can lead to cardiovascular disease. Untreated hypertension has clinical consequences such as coronary artery disease, stroke or kidney failure. Diltiazem hydrochloride (DH), a calcium-channel blocker, and perindopril erbumine (PE), an inhibitor of the angiotensin converting enzyme are used for the management of hypertension. OBJECTIVE: This project will examine the effect of microneedle rollers on the transport of DH and PE across pig ear skin. The use of the transcutaneous route of administration reduces and in sometimes eliminates the trauma and pain associated with injections. Furthermore, there is increased patient compliance. The purpose of this project was to study the effect of stainless steel microneedles on the transdermal delivery of DH and PE. METHOD: We utilized vertical Franz diffusion cells to study in vitro transport of DH and PE across microneedle- treated pig ear skin. Confocal laser scanning microscopy (CLSM) was used to characterize microchannel depth. Transdermal flux values were determined from the slope of the linear portion of the cumulative amount versus time curve. RESULTS: There was a 113.59-fold increase in the transdermal permeation of DH following the application of microneedle roller compared to passive diffusion. CONCLUSION: In the case of PE, there was an 11.99-fold increase in the drug transport across pig skin following the application of microneedle rollers in comparison with passive diffusion. Student's t-test and Mann-Whitney's rank sum test were used to determine statistically significant differences between experimental and control groups.

Dual-guild herbivory disrupts predator-prey interactions in the field.

Plant defenses often mediate whether competing chewing and sucking herbivores indirectly benefit or harm one another. Dual-guild herbivory also can muddle plant signals used by specialist natural enemies to locate prey, further complicating the net impact of herbivore-herbivore interactions in naturally diverse settings. While dual-guild herbivore communities are common in nature, consequences for top-down processes are unclear, as chemically mediated tri-trophic interactions are rarely evaluated in field environments. Combining observational and experimental approaches in the open field, we test a prediction that chewing herbivores interfere with top-down suppression of phloem feeders on Brassica oleracea across broad landscapes. In a two-year survey of 52 working farm sites, we found that parasitoid and aphid densities on broccoli plants positively correlated at farms where aphids and caterpillars rarely co-occurred, but this relationship disappeared at farms where caterpillars commonly co-occurred. In a follow-up experiment, we compared single and dual-guild herbivore communities at four local farm sites and found that caterpillars (P. rapae) caused a 30% reduction in aphid parasitism (primarily by Diaeretiella rapae), and increased aphid colony (Brevicoryne brassicae) growth at some sites. Notably, in the absence of predators, caterpillars indirectly suppressed, rather than enhanced, aphid growth. Amid considerable ecological noise, our study reveals a pattern of apparent commensalism: herbivore-herbivore facilitation via relaxed top-down suppression. This work suggests that enemy-mediated apparent commensalism may override constraints to growth induced by competing herbivores in field environments, and emphasizes the value of placing chemically mediated interactions within their broader environmental and community contexts.

Environmental transport of endogenous dairy manure estrogens.

Although estrogens originating from dairy manure applied to agricultural soils as a fertilizer can potentially contaminate surface water and groundwater, the variables that control transport are poorly understood. Our objective was to assess the potential for off-site movement of endogenous dairy cattle estrogens when manure is applied on fields at agronomically relevant fertilization rates. Estrone (E1), 17α-estradiol (α-E2), and 17ß-estradiol (ß-E2) were used in laboratory sorption, desorption, and transformation incubations with both manure and an agriculturally relevant soil. Sorption on manure containing 44% organic carbon exceeded sorption on soil containing 0.8% organic carbon by 20 to 150 times, following the pattern of ß-E2 > α-E2 > E1. Approximately 20% of E1 and 17% of α-E2 were desorbed from manure, whereas only about 4% of ß-E2 was desorbed. Thirty to seventy percent of α-E2 and ß-E2 were converted to E1 in soil and manure, making it imperative that transformation reactions be considered when predicting transport and potential biological effects in the environment. Overall results indicate that high organic carbon concentrations and relatively low amounts of desorption inhibit the potential for off-site transport of endogenous dairy manure estrogens.

The Influence of Solid Microneedles on the Transdermal Delivery of Selected Antiepileptic Drugs.

The aim of this project was to examine the effect of microneedle rollers on the percutaneous penetration of tiagabine hydrochloride and carbamazepine across porcine skin in vitro. Liquid chromatography-mass spectrometric analysis was carried out using an Agilent 1200 Series HPLC system coupled to an Agilent G1969A TOF-MS system. Transdermal flux values of the drugs were determined from the steady-state portion of the cumulative amount versus time curves. Following twelve hours of microneedle roller application, there was a 6.74-fold increase in the percutaneous penetration of tiagabine hydrochloride (86.42 ± 25.66 µg/cm²/h) compared to passive delivery (12.83 ± 6.30 µg/cm²/h). For carbamazepine in 20% ethanol, passive transdermal flux of 7.85 ± 0.60 µg/cm²/h was observed compared to 10.85 ± 0.11 µg/cm²/h after microneedle treatment. Carbamazepine reconstituted in 30% ethanol resulted in only a 1.19-fold increase in drug permeation across porcine skin (36.73 ± 1.83 µg/cm²/h versus 30.74 ± 1.32 µg/cm²/h). Differences in flux values of untreated and microneedle-treated porcine skin using solid microneedles for the transdermal delivery of tiagabine were statistically significant. Although there were 1.38- and 1.19-fold increases in transdermal flux values of carbamazepine when applied as 20% and 30% ethanol solutions across microneedle-treated porcine skin, respectively, the increases were not statistically significant.

An ecological risk assessment of pesticides and fish kills in the Sixaola watershed, Costa Rica.

Along the southeastern coast of Costa Rica, a variety of pesticides are intensively applied to produce export-quality plantains and bananas. In this region, and in other agricultural areas, fish kills are often documented by local residents and/or in the national news. This study examines principal exposure pathways, measured environmental concentrations, and selected toxicity thresholds of the three most prevalent pesticides (chlorpyrifos, terbufos, and difenoconazole) to construct a deterministic risk assessment for fish mortality. Comparisons of observed pesticide concentrations, along with estimated biological effects and observations during actual fish kills, highlight gaps in knowledge in correlating pesticide environmental concentration and toxicity in tropical environments. Observations of fish kill events and measured pesticide concentrations in the field, along with other water quality indicators, suggest that a number of environmental conditions can interact to cause fish mortality and that current species toxicity datasets may not be applicable for estimating toxicological or other synergistic effects, especially in tropical environments.

Reconstructing the history of mining and remediation in the Coeur d'Alene, Idaho Mining District using lake sediments.

Mining that began in the late 1800s intensified during World War II contaminating Lake Coeur d'Alene sediments with potentially toxic elements. We used 80y of the sediment record to reconstruct metal(loid) loadings to the lake and quantitatively evaluate the effectiveness of tailings management. Sediment core analysis for pollen, chronological markers, and metal(loid)s permitted stratigraphic reconstruction showing that contaminant loading decreased after tailings pond construction, but that most metal(loid) concentrations exceed recommended limits. Arsenic concentrations (250-450 mg kg(-)(1)) at the sediment-water interface are potentially toxic; however, low P concentrations in recent sediments (1.0-1.4 mg kg(-)(1)) inhibit eutrophication and the concomitant release of soluble As. Zinc (3 g kg(-)(1)), Cd (10 mg kg(-)(1)), Ag (10 mg kg(-)(1)), and Cu (90 mg kg(-)(1)) concentrations are now lower than in sediments deposited during active mining, but remain an environmental concern. Sedimentary Cr and Pb concentrations have not changed in the last 50y, because tailings continue to enter the lake. Although modern Cr concentrations (40 mg kg(-)(1)) are unlikely to cause toxicity, current Pb concentrations (4 g kg(-)(1)) exceed acceptable limits, creating challenges for remediation. Strategies to manage other mining-contaminated watersheds should include consideration of elemental differences when evaluating remediation effectiveness.

Simultaneous quantification of sinigrin, sinalbin, and anionic glucosinolate hydrolysis products in Brassica juncea and Sinapis alba seed extracts using ion chromatography.

Although mustards such as Sinapis alba and Brassica juncea contain glucosinolates (sinalbin and sinigrin, respectively) that hydrolyze to form biopesticidal products, routine quality control methods to measure active ingredients in seed and seed meals are lacking. We present a simple and fast ion chromatography method for the simultaneous quantification of sinigrin, sinalbin, and anionic hydrolysis products in mustard seed to assess biological potency. Optimum conditions include isocratic elution with 100 mM NaOH at a flow rate of 0.9 mL/min on a 4 × 210 mm hydroxide-selective anion-exchange column. All anion analytes including sinigrin, sinalbin, SO4(2-), and SCN(-) yielded recoveries ranging from 83 to 102% and limits of detection ≤0.04 mM, with samples displaying little interference from plant matrix components. Sample preparation is minimized and analysis times are shortened to <90 min as compared with previous methods that took days and multiple instruments.

Antioxidant extraction from mustard (Brassica juncea) seed meal using high-intensity ultrasound.

Brassicaceae oilseeds provide feedstocks for the biofuels industry, but value-added coproducts are necessary to supply financial incentives for increased production. Our objective was to use high-intensity ultrasound to optimize extraction of antioxidants from mustard (Brassica juncea) seed meal. The ultrasound-assisted extraction (UAE) variables included temperature, solvent-to-material ratio, sonication duration, and EtOH concentration. Extracts were analyzed for total phenolics content (TPC), antioxidant activity, and sinapine content. Conventional extraction using water and 70% EtOH (v/v) at 80 °C for 3×30 min yielded 7.83 ± 0.07 and 8.81 ± 0.17 mg sinapic acid equivalents (SAE)/g meal, respectively. UAE extraction at 40 °C for 30 min yielded similar phenolics content (8.85 ± 0.33 mg SAE/g meal) as conventional hot ethanolic extraction, but required less time and lower temperature. The highest TPC (13.79 ± 0.38 mg SAE/g meal) was in the 7-d aqueous extracts. Sonicated solutions of pure sinapine and sinapic acid showed 1st-order reaction kinetics with greater degradation of isolated compounds than those present in extracts. Sinapine contained in extracts showed insignificant (P < 0.05) degradation after 30 min of sonication. Our research indicates that ultrasound treatment can assist the extraction of antioxidants from B. juncea meal by reducing both the temperature and time requirement without significant degradation of the primary antioxidants present.

Mustard seed meal mixtures: management of Meloidogyne incognita on pepper and potential phytotoxicity.

Meals produced when oil is extracted from seeds in the Brassicaceae have been shown to suppress weeds and soilborne pathogens. These seed meals are commonly used individually as soil amendments; the goal of this research was to evaluate seed meal mixes of Brassica juncea (Bj) and Sinapis alba (Sa) against Meloidogyne incognita. Seed meals from Bj 'Pacific Gold' and Sa 'IdaGold' were tested alone and in combinations to determine rates and application times that would suppress M. incognita on pepper (Capsicum annuum) without phytotoxicity. Rates of soil application (% w/w) for the phytotoxicity study were: 0.5 Sa, 0.2 Bj, 0.25 Sa + 0.25 Bj, 0.375 Sa + 0.125 Bj, 0.125 Sa + 0.375 Bj, and 0, applied 0 - 5 weeks before transplant. Overall, 0.2% Bj was the least toxic meal to pepper seedlings. By comparison, 0.5% S. alba seed meal did not reduce lettuce (Lactuca sativa) seed germination at week 0, but all seed meal treatments containing B. juncea prevented or significantly reduced germination at week 0. The seed meals did not affect lettuce seed germination at weeks 1-5, but hypocotyl growth was reduced by all except 0.2% Bj at weeks 1, 4 and 5. Brassica juncea and Sa meals were tested for M. incognita suppression at 0.2, 0.15, 0.1 and 0.05%; mixtures were 0.1% Sa + 0.1% Bj, 0.15% Sa + 0.05% Bj, and 0.05% Sa + 0.15% Bj. All treatments were applied 2 weeks before transplant. The 0.2% Bj and 0.05% Sa + 0.15% Bj treatments overall had the longest shoots and highest fresh weights. Eggs per g root were lowest with 0.1 - 0.2% Bj amendments and the seed meal mixtures. The results indicate that Bj and some Bj + Sa mixtures can be applied close to transplant to suppress M. incognita populations on pepper; consequently, a seed meal mixture could be selected to provide activity against more than one pest or pathogen. For pepper, care should be taken in formulating mixtures so that Sa rates are low compared to Bj.

Selenium biogeochemical cycling and fluxes in the hyporheic zone of a mining-impacted stream.

The influence of hyporheic exchange on selenium (Se) biogeochemistry and mobility in sediments is unknown. A multiscale investigation of Se biogeochemistry in the hyporheic zone of East Mill Creek (EMC), southeastern Idaho, USA, was performed using in situ surface water and pore water geochemical measurements, a field-based stream tracer test, and energy-dependent micro synchrotron X-ray fluorescence (mu-SXRF) measurements of Se speciation in sediments. The active hyporheic zone was determined to be 12 +/- 3 cm. Pore water redox profiles indicated that a transition to suboxic conditions begins at approximately 6 cm. Modeling pore water Se and solid phase analysis suggested Se uptake is occurring. Micro-SXRF analysis of sediments showed reduced elemental Se or selenides throughout the profile and selenite in surface sediments. Field geochemical measurements and microscale analysis both support the hypothesis that reduction in the hyporheic zone promotes sequestration of surface water Se.

Pesticide sequestration in passive samplers (SPMDs): considerations for deployment time, biofouling, and stream flow in a tropical watershed.

Semi-permeable membrane devices (SPMDs) provide an informative and cost-effective approach for monitoring contaminants in remote tropical streams. Estimation and interpretation of contaminant concentrations in streams derived from SPMDs can vary based on a number of environmental factors, including stream flow, biofouling, and deployment time. In three one-month long trials, SPMDs were concurrently deployed for 4, 15, and 28 days at three stream sites in an extensive agricultural area of southeastern Costa Rica. Water, bottom sediment, and suspended solids grab samples were also collected and several environmental variables were monitored at corresponding time intervals during each month-long study period. At all three sites, SPMD concentrations of the widely used insecticide chlorpyrifos increased with deployment time, with no relationship between SPMD biofouling and pesticide sequestration. Differences in SPMD chlorpyrifos sequestration among sites are likely due to differences in stream chlorpyrifos concentration rather than differences in SPMD sampling rates. The longer exposure period of SPMDs allowed for the detection of lower concentrations of chlorpyrifos, terbufos, and difenoconazole compared to water grab samples. In addition to the use of appropriate performance reference compounds (PRCs), other environmental variables such as stream turbidity, flow regime, stream morphology, and knowledge of pesticide application methods are important considerations for optimizing SPMD deployment and data interpretation in tropical regions.

Brassicaceae tissues as inhibitors of nitrification in soil.

Brassicaceae crops often produce an unexplained increase in plant-available soil N possibly related to bioactive compounds produced from glucosinolates present in the tissues. Our objective was to determine if glucosinolate-containing tissues inhibit nitrification, thereby potentially explaining this observation. Ammonium, NO(2)(-), and NO(3)(-) N were measured in soils amended with Brassicaceae ( Isatis tinctoria L., Brassica napus L., Brassica juncea L., and Sinapis alba L.) tissues containing different glucosinolate types and concentrations or Kentucky bluegrass ( Poa pratensis L.) residues with equivalent C/N ratios as the Brassicaceae samples. There was greater accumulation of NH(4)(+) N in soils amended with tissues containing high glucosinolate concentrations as compared to soils amended with tissues containing no or low glucosinolate concentrations. Nitrite N was detected only in soils amended with Brassicaceae tissues having the highest glucosinolate concentrations. The positive correlation of both NH(4)(+) and NO(2)(-) N accumulation with the glucosinolate concentration indicates the participation of glucosinolate hydrolysis products in nitrification inhibition.

Ecology of sulfate-reducing bacteria in an iron-dominated, mining-impacted freshwater sediment.

A legacy of lead and silver mining in its headwaters left Lake Coeur d'Alene, Idaho with a sediment body that is highly reduced and contains up to 100 g kg(-1) iron and a smaller fraction of chemically active sulfide phases. The dynamic character of these sulfides and their importance for the sequestering of contaminating trace elements prompted this study of the sulfate-reducing bacteria (SRB) involved in their production. We estimated parameters indicative of the distribution and activity of SRB in relation to season, site, and depth. Most probable number estimates and quantitative PCR assays of an SRB-specific functional gene, alpha-adenosine 5'-phosphosulfate reductase, indicated 10(3) to 10(6) cultivable cells and 10(5) to 10(7) gene copy numbers g(-1) dry wt sediment, respectively. Although culture-based estimates of SRB abundance correlated poorly with site, season, depth, total S, or pore water SO(4), non-culture-based estimates of SRB abundance were markedly higher at contaminated sites and positively correlated with pore water SO(4). Ex situ estimates of (35)SO(4) respiration and acid volatile sulfides abundance also showed strong among-site effects, indicating elevated sulfidogenesis at contaminated sites. These observations support the view that biogenic sulfides may act in concert with reduced iron to retain soluble metal(loid)s in the solid phase.