Variations In Chemical Concentrations Research Articles

Physicochemical Hydrodynamics of Particle Diffusiophoresis Driven by Chemical Gradients

Chemical gradients, the spatial variations in chemical concentrations and components, are omnipresent in environments ranging from biological and environmental systems to industrial processes. These thermodynamic forces often play a central role in driving transport processes taking place in such systems. This review focuses on diffusiophoresis, a phoretic transport phenomenon driven by chemical gradients. We begin by revisiting the fundamental physicochemical hydrodynamics governing the transport. Then we discuss diffusiophoresis arising in flow systems found in natural and artificial settings. By exploring various scenarios where chemical gradients are encountered and exploited, we aim to demonstrate the significance of diffusiophoresis and its state-of-the-art development in technological applications.

Swimming Behavior of Daphnia magna Is Altered by Pesticides of Concern, as Components of Agricultural Surface Water and in Acute Exposures

Pesticides with novel modes of action including neonicotinoids and anthranilic diamides are increasingly detected in global surface waters. Little is known about how these pesticides of concern interact in mixtures at environmentally relevant concentrations, a common exposure scenario in waterways impacted by pesticide pollution. We examined effects of chlorantraniliprole (CHL) and imidacloprid (IMI) on the sensitive invertebrate, Daphnia magna. Exposures were first performed using surface waters known to be contaminated by agricultural runoff. To evaluate the seasonal variation in chemical concentration and composition of surface waters, we tested surface water samples taken at two time points: during an extended dry period and after a first flush storm event. In surface waters, the concentrations of CHL, IMI, and other pesticides of concern increased after first flush, resulting in hypoactivity and dose-dependent photomotor responses. We then examined mortality and behavior following single and binary chemical mixtures of CHL and IMI. We detected inverse photomotor responses and some evidence of synergistic effects in binary mixture exposures. Taken together, this research demonstrates that CHL, IMI, and contaminated surface waters all cause abnormal swimming behavior in D. magna. Invertebrate swimming behavior is a sensitive endpoint for measuring the biological effects of environmental pesticides of concern.

Chemical Concentration and Spatial Uniformity of a Premixing In-Line Injection System Attached to a Variable-Rate Orchard Sprayer

HighlightsA newly developed premixing in-line injection system attached to a variable-rate orchard sprayer was evaluated.Tests were conducted to verify the in-line injection system performance using a vertical spray patternator.Concentration accuracy and spatial distribution uniformity were determined with a fluorescent tracer.Uniform spray mixtures were obtained for different spray viscosities and duty cycle combinations.Abstract. Pesticide spray application efficiency is highly dependent on the chemical concentration accuracy and spatial distribution uniformity. In this study, the performance of a newly developed premixing in-line injection system was evaluated when it was attached to a laser-guided, pulse width modulated (PWM), variable-rate orchard sprayer. The chemical concentration accuracy was determined with respect to spray deposition with a fluorescent tracer, and the spatial distribution uniformity was determined with spray deposits at different heights on a vertical spray patternator. Outdoor tests were conducted with 27 combinations of target chemical concentration (1.0%, 1.5%, and 2.0%), viscosity of the simulated pesticide (1.0, 12.0, and 24.0 mPa·s), and various spray outputs manipulated with PWM duty cycles. For each injection loop, the amounts of the chemical concentrate and water discharged into the mixing line were measured separately in response to preset target concentrations. The results showed that the measured concentrations were consistent across the patternator heights, spray viscosities, and duty cycle combinations. For all treatments, the mean absolute percentage error (MAPE) of the measured concentration was 6.96%, indicating that the concentration accuracy of the system was acceptable. The mean coefficient of variation was 3.35%, indicating that the spatial distribution uniformity of the system was in the desirable range. In addition, there was little variation in chemical concentration for spray mixtures collected at different heights on the patternator. Thus, the premixing in-line injection system could adequately dispense chemical concentrate and water to produce accurate concentrations and uniform spray mixtures for variable-rate nozzles to discharge to targets. Keywords: Environment protection, Precision pesticide application, Laser-guided sprayer, Tank mixture disposal, Specialty crop.

Community De-fluoridation - Experience in Kaiwara Village, Chikkaballapur District, Karnataka, India

Background and objective: Reverse osmosis technique is an adequate method for treating ground water for reducing the burden of abnormal levels of fluorides. The method protects the general population from diseases associated with high fluoride levels in the body. The objective of the present study was to assess the suitability and sustainability of reverse osmosis technology for community de-fluoridation of water used for cooking and drinking purposes in Kaiwara village, Karnataka. Methodology: This interventional study was conducted between July 2012 and June 2014 at Kaiwara village, Karnataka using reverse osmosis technique for de-fluoridation of water used for drinking and cooking. Complete chemical analysis of water was done before intervention, and processed water supplying the village was tested every six months after intervention for about two years. The variation in chemical concentrations of various components were analysed. Results: The mean baseline level of fluoride in untreated water was 2.075 mg/dl (above the safety limit), which dropped to 0.08 mg/dl at the end of first six months following the intervention, 0.042 mg/dl in 12 months, 0.1 mg/dl at 18 months and 0.01 mg/dl at 24 months after intervention, which were all below the safety limits for India in the treated water. The mean total dissolved solids in the water was 542.25 mg/dl in the untreated water, which dropped to zero after the first six months, remained at zero in the next six months, rose to 120 mg/dl at 18 months and then dropped to 70 mg/dl at 24 months in the treated water. The observed values were reduced significantly. Discussion: The study concluded that it is possible to set up a community de-fluoridation plant using reverse osmosis technique at Kaiwara village, Karnataka which is economically sustainable and acceptable by local population.

Multimineral reactions controlling secondary phase evolution in a hyperalkaline plume

This paper presents a modelling study of the influence of a hyperalkaline leachate on a host rock in a geological disposal facility for low- to intermediate-level nuclear waste disposal, when compared with a 15-year experiment designed to simulate the geochemical and mineralogical evolution of the system. The hyperalkaline leachate may be produced by the interaction of groundwater with the cementitious backfill surrounding the waste form. The rock sample is from the Borrowdale Volcanic Group, which comprises orthoclase, quartz, dolomite, muscovite, haematite and calcite as the major mineral phases, with various kinetic dissolution/precipitation rates. Multimineral reactions with the multiple chemicals in the leachate are responsible for the variation in chemical concentration and temporal evolution of different primary and secondary phases observed in the experimental study. The temporal variation in the concentrations of calcium (Ca2+), silicate (SiO3 2−), magnesium (Mg2+) and carbonate (CO3 2−) ions and pH has been modelled, which agrees well with the experimental results. The mineral evolution process has confirmed that dolomite and calcium silicate hydrate (CSH) gel (CSH phases) will dissolve and generate new secondary phases, such as calcite and saponite-K over the 15-year experiment.

Patterns and Variability of Endocrine-disrupting Chemicals During Pregnancy: Implications for Understanding the Exposome of Normal Pregnancy.

The exposome is a novel research paradigm offering promise for understanding the complexity of human exposures, including endocrine-disrupting chemicals (EDCs) and pregnancy outcomes. The physiologically active state of pregnancy requires understanding temporal changes in EDCs to better inform the application of the exposome research paradigm and serve as the impetus for study. We randomly selected 50 healthy pregnant women with uncomplicated pregnancies from a pregnancy cohort who had available serum/urine samples in each trimester for measuring 144 persistent and 48 nonpersistent EDCs. We used unsupervised machine-learning techniques capable of handling hierarchical clustering of exposures to identify EDC patterns across pregnancy, and linear mixed-effects modeling with false-discovery rate correction to identify those that change over pregnancy trimesters. We estimated the percent variation in chemical concentrations accounted for by time (pregnancy trimester) using Akaike Information Criterion-based R methods. Four chemical clusters comprising 80 compounds, of which six consistently increased, 63 consistently decreased, and 11 reflected inconsistent patterns over pregnancy. Overall, concentrations tended to decrease over pregnancy for persistent EDCs; a reverse pattern was seen for many nonpersistent chemicals. Explained variance was highest for five persistent chemicals: polybrominated diphenyl ethers #191 (51%) and #126 (47%), hexachlorobenzene (46%), p,p'-dichloro-diphenyl-dichloroethylene (46%), and o,p'-dichloro-diphenyl-dichloroethane (36%). Concentrations of many EDCs are not stable across pregnancy and reflect varying patterns depending on their persistency underscoring the importance of timed biospecimen collection. Analytic techniques are available for assessing temporal patterns of EDCs during pregnancy apart from physiologic changes.

A 15-year record (2001–2015) of the ratio of nitrate to non-sea-salt sulfate in precipitation over East Asia

Abstract. Acidifying species in precipitation can have severe impacts on ecosystems. The chemical composition of precipitation is directly related to the amount of precipitation; accordingly, it is difficult to identify long-term variation in chemical concentrations. The ratio of the nitrate (NO3−) to non-sea-salt sulfate (nss-SO42−) concentration in precipitation on an equivalent basis (hereinafter, Ratio) is a useful index to investigate the relative contributions of these acidifying species. To identify the long-term record of acidifying species in precipitation over East Asia, the region with the highest emissions worldwide, we compiled ground-based observations of the chemical composition of precipitation over China, Korea, and Japan from 2001 to 2015 based on the Acid Deposition Monitoring Network in East Asia (EANET). The spatial coverage was limited, but additional monitoring data for Japan, southern China, and northern China around Beijing were utilized. The period of analysis was divided into three phases: Phase I (2001–2005), Phase II (2006–2010), and Phase III (2011–2015). The behaviors of NO3− and nss-SO42− concentrations and hence the Ratio in precipitation were related to these precursors. The anthropogenic NOx and SO2 emissions and the NOx ∕ SO2 emission ratio were analyzed. Further, satellite observations of the NO2 and SO2 column density to capture the variation in emissions were applied. We found that the long-term trend in the NO3− concentration in precipitation was not related to the variation in NOx emission and the NO2 column. In comparison, the nss-SO42− concentration in precipitation over China, Korea, and Japan was partially connected to the changes in SO2 emissions from China, but the trends were not significant. The long-term trends of Ratio over China, Korea, and Japan were nearly flat during Phase I, increased significantly during Phase II, and were essentially flat again during Phase III. This variation in Ratio in East Asia clearly corresponded to the NOx ∕ SO2 emission ratio and the NO2 ∕ SO2 column ratio in China. The initial flat trend during Phase I was due to increases in both NOx and SO2 emissions in China, the significantly increasing trend during Phase II was triggered by the increase in NOx emissions and decrease in SO2 emissions in China, and the return to a flat trend during Phase III was caused by declines in both NOx and SO2 emissions in China. These results suggest that emissions in China had a significant impact not only on China but also on downwind precipitation chemistry during the 15-year period of 2001–2015. In terms of wet deposition, the NO3− wet deposition over China, Korea, and Japan did not change dramatically, but the nss-SO42− wet deposition declined over China, Korea, and Japan from Phase II to III. These declines were caused by a strong decrease in the nss-SO42− concentration in precipitation accompanied by a reduction in SO2 emission from China, which counteracted the increase in precipitation. These findings indicated that the acidity of precipitation shifted from sulfur to nitrogen.

Tensile properties of AlCrCoFeCuNi glassy alloys: A molecular dynamics simulation study

High-entropy alloys (HEAs) are among multi-component alloys with attractive microstructures and mechanical properties. In this study, molecular dynamics simulation was used to determine the tensile behaviour of glassy AlxCrCoFeCuNi HEAs from 300°K to 1300°K. For this purpose, this alloy with variations in chemical concentration of aluminum were heated and then cooled at a high cooling rate of 21.1×1012K/s. Results from radial distribution functions (RDF) and common neighbor analysis (CNA) indicated that no crystalline structures were formed for these glassy alloys. The deformation behaviour and mechanisms of the glassy alloys at room and high temperatures and various strain rates were investigated and reported. The tensile test results showed that the yield stress decreased markedly as temperature was increased for all the alloys. The alloys exhibited superplastic behaviour for all test conditions. More importantly, by increasing the molar ratio of aluminum from 0.5 to 3.0, the yield stress and elastic modulus decreased considerably. Also, the yield stress increased with increasing the strain rate for all samples with different aluminum concentrations. Free volume content of the alloys as well as shear banding were evaluated for these alloys to aid explanation of these results.

Effects of dynamic synapses, neuronal coupling, and time delay on firing of neuron

Neuronal firing plays a key role in the neuronal information transmission, and different neuronal firing patterns are reported, such as spiking, bursting. A number of neuron models are introduced to reproduce the firing patterns of single neuron or neuronal network. The key factors determining the firing pattern gain more and more attention in the study of neuron system, such as noise, network topology. Noise is able to induce sub-or super-threshold coherent neuronal firing easily, and a number of coherence resonances are reported in the noise induced firing. The network topology determines the synchronization of the firing patterns of the neuronal network, and the change of network topology may induce fruitful synchronization transitions. It is well known that synapses exhibit a high variability with a diverse origin during information transmission, such as the stochastic release of neurotransmitters, variations in chemical concentration through synapses, and spatial heterogeneity of synaptic response over dendrite tree. The collective effect of all of these factors might result in the notion of dynamic synapses. In reality, the neuronal network often involves time delay due to the ?nite signal propagation time in biological networks. Recently, neuronal networks with time delay have received considerable attention. Delay-sustained neuronal firing patterns may be relevant to neuronal networks for establishing a concept of collective information processing in the presence of delayed information transmission. According to the above-mentioned motivations, the firing dynamics of the single postsynapic neuron is investigated based on a simple postsynaptic neuron model by using numerical simulation and Fourier transform analysis. In this model, the postsynapic neuron receives dynamic synaptic currents from a population of presynaptic neurons. It is found that the firing rate resonance between the pre-and postsynaptic neuron determines the firing of the postsynaptic neuron. Stimulus currents in specific frequency range are easy to stimulate postsynaptic neuron firing. The random currents released from dynamic synapses determine the postsynaptic firing rate. Then the single postsynaptic neuron is extended to a neuronal network, in which 100 neurons connect to its 4 nearest neighbors regularly and receive delayed synaptic currents from connected neurons. All the neurons in the network receive the same dynamic synaptic currents from the presynaptic neurons. The results show that the synaptic coupling in the network is able to promote the neuron firing in the network, and time delay in the synaptic coupling could reinforce the promotion, but the mode of the promotion is not changed.

How the soil chemical composition is affected by seven tree species planted at a contaminated and remediated site

Abstract. Trees modify the physico-chemical and biological properties of the soil underneath. Here we present results for seven tree species planted at a site that was contaminated by a mine spill – after which soil was cleaned up and remediated – and later was afforested. We studied the chemical composition (24 elements) in five ecosystem compartments (leaves, forest floor, roots, topsoil and deep soil). The variation in chemical concentration was highest at the level of canopy leaves and lowest at deep soil. The identity of tree species significantly affected the composition of all elements in the canopies but none in the deep soil underneath. Although the observed tree effects on topsoil chemistry were weak, the footprint is expected to be reinforced with age of the plantation, contributing to the phytostabilization of contaminating elements and to the carbon sequestration.

Mapping hotspots of underground water quality based on the variation of chemical concentration in Amman, Zarqa and Balqa regions, Jordan

This study uses geographic information systems to map the hotspots level changes in underground water quality based on pH, nitrate and conductivity in Amman, Zarqa and Balqa regions, Jordan using data from 57 wells. The chemical concentration for each parameter was obtained from the Water Authority of Jordan. The data were tested according to ISO/IEC 17025 standards by the Jordan Inorganic Laboratory of the Laboratories and Quality Department of Water Authority for 2004 and 2010 and were processed using Getis-Ord Gi statistics. The study indicated that there are periodic fluctuations for the values of selected chemical elements of groundwater that are localized, creating contamination hotspots within the study regions. The pH, nitrate and conductivity all indicated specific hotspots of higher than average values in 2004 and 2010 in the Zarqa region. The evidence indicates that there are two major localized areas of high value for all parameters centered in the western Zarqa region, an area dominated by urban infrastructure and irrigated lands. These findings have implications for the management of aquifer water quality through the identification of high-value hotspots. Because the aquifers in the regions are connected, understanding the hotspots with high pH, nitrate and conductivity values may enable improvements in the water quality across the aquifer systems in the regions.

Generation of Chemical Concentration Gradients in Mobile Droplet Arrays via Fragmentation of Long Immiscible Diluting Plugs

We report a one-step passive microfluidic technique to generate arrays of moving droplets containing variation of chemical concentration between individual drops. We find that a concentration gradient can be established in a long diluting plug by on-chip dilution and extraction of samples via orthogonal coalescence of the plug with a static array of sample drops. The diluting plug containing the gradient is subsequently fragmented by a droplet generator. We show that the technique is flexible, as the dilution range can be tuned by a variety of control parameters including the carrier fluid flow rate, volume of diluting plugs, and stationary drops. We also find that the concentration gradients have a fine resolution and are reproducible to within 2% relative standard deviation. As one demonstrative application, we show the suitability of the technique for generating a dose-response curve for an enzyme inhibition assay. Because of the ability to inject multiple plugs, our technique has the potential for unlimited as well as sequential dilution of a series of substrates. Thus, our method could be valuable as a high-throughput and high-resolution screening tool for assays that require interrogation of the response of one or more target species to numerous distinct chemical concentrations.

Soil‐Aggregate‐Scale Heterogeneity in Microbial Selenium Reduction

Given the role of Se as both an environmental contaminant and a micronutrient, the microbial reduction and subsequent sequestration of bioavailable Se in soils are of great ecological interest. Primary particles in surface soils are typically bound into loosely packed, microporous aggregates, which may be critical spatial units in determining the fate of Se in soils. Surrounded by macropores where preferential flow rapidly advects dissolved compounds, soil aggregates are domains of slow diffusive transport where spatial variations in chemical concentrations and biogeochemical reactions can prevail. We conducted a series of controlled flow‐through experiments utilizing three‐dimensional, artificial soil aggregates (2.5‐cm i.d.) surrounded by a macropore. Aggregates were composed of either quartz sand or ferrihydrite‐coated sand inoculated with one of two Se‐reducing bacteria (Thauera selenatis or Enterobacter cloacae SLD1a‐1). Selenite export rates varied between 0.02 ± 0.01 and 3.4 ± 0.2 nmol h−1 g−1 as a function of aeration condition and input solution composition (higher SeO42− or C‐source concentrations led to higher SeO32− export). Oxic input conditions significantly decreased Se reduction; however, the detection of SeO32− in effluent samples indicates the occurrence of anoxic microzones within aggregates. Furthermore, we found that solid‐phase concentrations of reduced Se increased toward the core of aggregates and are estimated to at least double within the first millimeter into the aggregate under all conditions investigated. This indicates that concentrations of reduced Se may generally be expected to increase with distance from the advection boundary (macropore) inside aggregates, which would imply that soils with larger aggregates retain more Se.

Hydrothermal Synthesis of Zinc Oxide Nanowires on Kevlar using ALD and Sputtered ZnO Seed Layers

AbstractLow temperature hydrothermal methods allow for growth of nanowires on novel substrates. We examine the impact of variations in chemical concentration, time, temperature, and seed layer on nanowire (NW) growth and crystallite formation. The majority of growth (NWs and crystallites) was found to occur within the first two hours. Lower Zn(NO3)2 concentrations produced a reduction in the undesired large crystallites, whereas hexamethylene tetramine (HMT) concentration did not largely impact crystallite density or nanowire morphology. Growth temperature appeared to impact NW diameter variation. Nanowires grow only on the ZnO seed layer and crystallites seem to attach preferentially to the bare Kevlar surface.

Change in MSW characteristics under recent management strategies in Taiwan

Reduction and recycling initiatives such as producer responsibility and pay-as-you-throw are being implemented in Taiwan. This paper presents a study assessing the impact of recently implemented municipal solid waste (MSW) reduction and recycling management strategies on the characteristics of waste feedstock for incineration in Taiwan. Through the periodic sampling of two typical MSW incineration plants, proximate and ultimate analyses were conducted according to standard methods to explore the influence of MSW reduction and recycling management strategies on incineration feed waste characteristics. It was observed that the annual amount of MSW generated in 2005 decreased by about 10% compared to 2003 and that the characteristics of MSW have changed significantly due to recent management strategies. The heating value of the MSW generated in Taiwan increased yearly by about 5% after program implementation. A comparison of the monthly variations in chemical concentrations indicated that the chlorine content in MSW has changed. This change results from usage reduction of PVC plastic due to the recycling fund management (RFM) program, and the food waste as well as salt content reduction due to the total recycling for kitchen garbage program. This achievement will improve the reduction of dioxin emissions from MSW incineration. In summary, management strategies must be conducted in tandem with the global trend to achieve a zero-waste-discharge country. When implementing these strategies and planning for future MSW management systems, it is important to consider the changes that may occur in the composition and characteristics of MSW over time.

Using landscape ecology to focus ecological risk assessment and guide risk management decision-making.

Ecological risk assessment (EcoRA) generally suffers from limited application of ecological knowledge in the definition and characterization of real-world sites. Not surprisingly, most remediation decisions, which follow, have little or no relationship to the valued ecological resources of the site or the broader region. The practice has evolved to favor engineering-based mitigation strategies, which eliminate excess chemical concentrations at sites, or otherwise break exposure pathways, but which may not be ecologically beneficial. The heavy emphasis of EcoRA on toxicity threshold levels tends to focus dollars on clean up of small areas or volumes with high concentrations. Moreover, intrusive remediation technologies often render an area uninhabitable to the very species that were to be protected. Infusion of ecological knowledge into EcoRA has been difficult. Most professional ecologists choose not to venture into the messy applied fields, leaving their impressive knowledge untapped. Moreover, narrowly defined responsibilities within government circles can limit cooperation and coordination. The realization that land use activities often have greater adverse consequences to wildlife than do chemicals provides an opportunity to change attitudes and practices. We are developing procedures that incorporate landscape features into the environmental management process. Specifically, we are using an iterative approach to: a) identify scenarios where habitat value is important in EcoRAs; b) guide selection of appropriate assessment species, i) keyed to wildlife distribution ranges; ii) keyed to a database of habitat suitability models; iii) cross-linked with the EPA exposure handbook species; iv) referenced to wildlife distributions (e.g., breeding bird survey); c) define data collection needs for reconnaissance-, screening-, and definitive-level characterization of habitat quality for potential assessment species; d) generate spatially explicit descriptions of habitat quality for various assessment species; and e) allocate exposure estimates using both habitat quality and spatial variations in chemical concentration. These refinements in theEcoRA process are expected to improve risk estimates and provide valuable information to be used instructuring risk management options. The approach can guide the planning process so that an assessment considers the most relevant species of the area and defines the relevant parameters to be measured. In risk characterization, these data are used to calculate more realistic exposure assessments. In guiding remediation, the approach logically considers a wider range of land management options than are considered at most sites today. For example, habitat enhancement can be used to draw animals away from contaminated zones. Contaminated localities that also have poor-quality habitat may be allowed to go through a slower, less costly bioremediation process until the risk level is lowered to acceptable levels. And direct comparisons of lost resources stemming from destructive remediation options can be assessed instead of merely focusing on the lowering of contaminant concentrations. This paper presents the conceptual foundation for incorporating landscape ecology into the risk assessment process.

Agricultural Chemicals in the Alluvial Aquifer of a Typical County of the Arkansas Delta

Statistical methods and a Geographic Information System (GIS) were used to investigate potential indicators of ground water vulnerability to agricultural chemical contamination in a representative area of the Mississippi River alluvial aquifer. A total of 47 wells were sampled for analysis of nitrate, phosphorus, potassium, and 13 pesticides commonly-used in the area. Ten soil and hydrogeologic variables and five ground water vulnerability indices were examined to explain the variations of chemical concentrations. The results showed that no individual soil or hydrogeologic variables or their linear combinations could explain more than 25% of the variation of the chemical concentrations. A quadratic response surface model with the values of confining unit thickness, slope, soil permeability, depth to ground water, and recharge rate accounted for 62% of the variation of nitrate, 43% of P, and 83% of K, suggesting that the interactions among soil and hydrogeologic variables were significant. Observed trends of decreasing nitrate and P concentrations with increasing well depth and/or depth to ground water seemed to correlate with carbonate equilibrium in the aquifer and more reduced environment with depth. In view of uncertainties involved, it was recognized that the limitations associated with input data resolution used in GIS and the formulation of leaching indices limited their use for predicting ground water vulnerability. Misuse of pesticides could be another factor that would complicate the relationships between pesticide concentrations and the vulnerability indices.

Organochlorine contaminant concentrations in eggs and their relationship to body size, and clutch characteristics of the female common snapping turtle (Chelydra serpentina serpentina) in lake Ontario, Canada

Statistical analyses were used to determine relationships between body size, clutch size and mass, and relative clutch mass and levels of organochlorine pesticides and seven polychlorinated biphenyl congeners in the eggs of adult female common snapping turtles (Chelydra serpentina serpentina). No significant correlations were found between body size (body mass, carapace length, carapace width, plastron length) and lipid normalized concentrations of p,p′-DDE, mirex, dieldrin, and polychlorinated biphenyl (PCB) congeners (IUPAC): #52, #105, #118, #138, #153, #180, #194, and the sum concentration of those congeners. Small sample size and clumping of data around the mode of the body size values prevented inferences of nonlinear relationships. It was concluded that body size and clutch characteristics are not strong or reliable predictors of the level of contaminants in snapping turtle eggs and that adjustment for those parameters would not reduce variation in contaminant levels among clutches. Other variables such as individual food preferences and/or foraging activities are more likely to cause variation in chemical concentrations among clutches of eggs within a population. In order to reduce interclutch variation in contaminant levels to 38.6–55.9% in snapping turtles, sample sizes of at least 15 clutches per site are recommended.

BOOM FLOW CHARACTERISTICS WITH DIRECT CHEMICAL INJECTION

ABSTRACT A metered rate of a tracer chemical was injected directly into the diluent stream at three points on a boom sprayer: immediately upstream of the pump, immediately downstream of the pump, and at the individual nozzles. Time from initiation of injection to achievement of uniform chemical concentration at the nozzles was measured. Uniformity of chemical concentration in the nozzle effluent both across the boom and with time was also monitored. As the injection point was moved downstream in the system, the transient time required to produce uniform chemical concentration in the nozzle effluent was reduced. Variations in chemical concentration in the nozzle effluent were usually increased as the injection point was moved farther downstream.

Time-related changes in snow chemistry — Ross Ice Shelf, Antarctica

Snow from seven two-meter deep pits on the Ross Ice Shelf has been analysed for Na, Mg, Ca and K. The concentrations vary with depth, the peaks and minima covering ranges of 10:1. The changes in concentration for all four elements were found to be coincident in depth at any one site. When concentrations are highest, elemental ratios are close to sea-water values, indicating a predominantly marine influence. At lower concentrations the chemical ratios are different from sea water and the Mg, Ca and K are enriched with respect to Na. The chemical profile characteristics have been found to be highly correlated between sites. The slopes of the regression lines describing the correlations provide a means for estimating the ratios of the snow accumulations at these sites. The ratios agree well with independent determinations of accumulation based upon β-activity measurements. The concentration changes do not appear to be entirely seasonal in nature. The present interpretation is that the variations in chemical concentrations are caused by meteorological events (storms) large enough to influence substantial geographical areas simultaneously. The frequency and intensity of these events are known to be greatest in autumn and spring, and hence there are probably some seasonal relationships, but these are expected to vary from year to year. The results obtained lead to the development of a hypothesis that the shearing stress conditions in the boundary layer in proximity to the Ross Ice Shelf have a strong influence on the concentrations and ratios of chemical components in the snow on the Shelf. High-shearing-stress conditions in the boundary layer in proximity to the Ross Ice Shelf are conducive to the production of extensive snow storms (particularly in the autumn months), over substantial areas of the Shelf. The trajectories of these storms across southern oceans suggests the sea surface as the principal source of chemical impurities observed in the snow over wide areas of the Shelf. Low-shearing-stress (stable) conditions lead to precipitation events in which the chemistry manifests elemental enrichment with respect to Na. Under these conditions the crustal origin impurities become a more predominant component of the snow chemistry.