Chemical Concentration Data Research Articles

Staying the course: chemical signal spatial properties and concentration mediate cross-stream motion in turbulent plumes

This study examined the role of broadly distributed sensor populations in chemosensory searching, especially cross-stream heading adjustment. We used three-dimensional laser-induced fluorescence to collect chemical concentration data simultaneously with behavior observations of actively tracking blue crabs (Callinectes sapidus). Our analysis indicates that the spatial distribution of the odorant concentration field is necessary and sufficient to mediate correct cross-stream motion, although concentration provides information that supplements that obtained from the spatial distribution. Crab movement is continually adjusted to maintain an upstream heading, with corrections toward the source modulated only in the presence of chemical cues. Crabs detect and respond to shifts in the position of the center-of-mass (COM) of the odorant concentration distribution as small as 5% of the leg span, which corresponds to ∼0.8-0.9 cm. The reaction time after a 5% threshold shift in the position of the COM is in the range of 2-4 s. Data also indicate that these steering responses are dependent on stimulus history or other characteristics of the plume, with crabs taking longer to respond in conditions with large-scale spatial meanders. Although cross-stream motion is determined by chemical signal inputs to receptors on the walking legs, crabs do make rotational movements in response to chemical signals impinging on the antennules. These rotational movements do not affect the direction of travel, but rather, determine the crab's body angle with respect to the flow. Interestingly, these body angles seem to represent a compromise between reducing drag and obtaining better chemical signal information, and this trade-off is resolved differently under different plume conditions.

Getting ahead: context-dependent responses to odorant filaments drive along-stream progress during odor tracking in blue crabs

The chemosensory signal structure governing the upstream progress of blue crabs to an odorant source was examined. We used a three-dimensional laser-induced fluorescence system to collect chemical concentration data simultaneously with behavior observations of actively tracking blue crabs (Callinectes sapidus) in a variety of plume types. This allowed us to directly link chemical signal properties at the antennules and legs to subsequent upstream motion while altering the spatial and temporal intermittency characteristics of the sensory field. Our results suggest that odorant stimuli elicit responses in a binary fashion by causing upstream motion, provided the concentration at the antennules exceeds a specific threshold. In particular, we observed a significant association between crab velocity changes and odorant spike encounters defined using a threshold that is scaled to the mean of the instantaneous maximum concentration. Thresholds were different for each crab, indicating a context-sensitive response to signal dynamics. Our data also indicate that high frequency of odorant spike encounters terminate upstream movement. Further, the data provide evidence that the previous state of the crab and prior stimulus history influence the behavioral response (i.e. the response is context dependent). Two examples are: (1) crabs receiving prior odorant spikes attained elevated velocity more quickly in response to subsequent spikes; and (2) prior acceleration or deceleration of the crab influenced the response time period to a particular odorant spike. Finally, information from both leg and antennule chemosensors interact, suggesting parallel processing of odorant spike properties during navigation.

Improved mapping of National Atmospheric Deposition Program wet-deposition in complex terrain using PRISM-gridded data sets

High-elevation regions in the United States lack detailed atmospheric wet-deposition data. The National Atmospheric Deposition Program/National Trends Network (NADP/NTN) measures and reports precipitation amounts and chemical constituent concentration and deposition data for the United States on annual isopleth maps using inverse distance weighted (IDW) interpolation methods. This interpolation for unsampled areas does not account for topographic influences. Therefore, NADP/NTN isopleth maps lack detail and potentially underestimate wet deposition in high-elevation regions. The NADP/NTN wet-deposition maps may be improved using precipitation grids generated by other networks. The Parameter-elevation Regressions on Independent Slopes Model (PRISM) produces digital grids of precipitation estimates from many precipitation-monitoring networks and incorporates influences of topographical and geographical features. Because NADP/NTN ion concentrations do not vary with elevation as much as precipitation depths, PRISM is used with unadjusted NADP/NTN data in this paper to calculate ion wet deposition in complex terrain to yield more accurate and detailed isopleth deposition maps in complex terrain. PRISM precipitation estimates generally exceed NADP/NTN precipitation estimates for coastal and mountainous regions in the western United States. NADP/NTN precipitation estimates generally exceed PRISM precipitation estimates for leeward mountainous regions in Washington, Oregon, and Nevada, where abrupt changes in precipitation depths induced by topography are not depicted by IDW interpolation. PRISM-based deposition estimates for nitrate can exceed NADP/NTN estimates by more than 100% for mountainous regions in the western United States.

CHEMISTRY VERSUS DATA DISPERSION: IS THERE A BETTER WAY TO ASSESS AND INTERPRET ARCHAEOMETRIC DATA?

Given the common use of chemical concentration data to define ceramic groups that aid in the exploration of ancient technology, trade and provenance, it is important to reflect on how we collectively establish and define both chemical groups and outliers. In this paper, we argue that commonly used data analysis procedures, such as principal component analysis and centred log‐ratio principal component analysis favoured in the examination of ceramic chemical data, although rapid and easy, may overlook existing chemical groups and outliers, especially when the ratio of non‐diagnostic to diagnostic elements is high. To evaluate whether geochemistry is more important than data dispersion in data assessment, we re‐examine chemical concentration data from previously published ceramic, clay and daub samples from the lower Ohio River Valley. We begin by briefly discussing steps we took to ensure that the data set reflects geochemical differences, rather than analytical or data transfer errors. Next, we use bivariate plots, as well as PCA and CLR–PCA, to examine different versions of our altered data, using varying numbers of element combinations. We propose that the careful examination of bivariate plots is critical in establishing the elements that should be included in PCA and other multivariate analyses.

Using TOUGHREACT to Model Laboratory Tests on the Interaction of NaNO3-NaOH Fluids with Sandstone Rock at a Deep Radionuclide Repository Site

TOUGHREACT V1.0 modeling was used to reproduce laboratory tests involving sandstone samples collected from a deep radionuclide repository site at the Siberia Chemical Plant, Seversk, Russia. Laboratory tests included injection of alkaline fluids into sandstone samples at 70°C. Some minerals were constrained in the model to precipitate or dissolve, according to laboratory test results. Modeling results were compared with observed test data (mineral phase changes, transient concentration data at the outlet of a sample column). Reasonable agreement was obtained between calculated and measured mineral phases (Na-smectite and kaolinite precipitation, quartz, microcline, chlorite, and muscovite dissolution). After a cation exchange option was used in the model, the most abundant secondary mineral generated was dawsonite, which corresponds to sodium carbonates observed in the sample after an injection test. Time-dependent chemical concentrations (transient chemical concentration data) at the outlet of the sample column qualitatively matched the data observed.

Household vacuum cleaners vs. the high-volume surface sampler for collection of carpet dust samples in epidemiologic studies of children

BackgroundLevels of pesticides and other compounds in carpet dust can be useful indicators of exposure in epidemiologic studies, particularly for young children who are in frequent contact with carpets. The high-volume surface sampler (HVS3) is often used to collect dust samples in the room in which the child had spent the most time. This method can be expensive and cumbersome, and it has been suggested that an easier method would be to remove dust that had already been collected with the household vacuum cleaner. However, the household vacuum integrates exposures over multiple rooms, some of which are not relevant to the child's exposure, and differences in vacuuming equipment and practices could affect the chemical concentration data. Here, we compare levels of pesticides and other compounds in dust from household vacuums to that collected using the HVS3.MethodsBoth methods were used in 45 homes in California. HVS3 samples were collected in one room, while the household vacuum had typically been used throughout the home. The samples were analyzed for 64 organic compounds, including pesticides, polycyclic aromatic hydrocarbons, and polychlorinated biphenyls (PCBs), using GC/MS in multiple ion monitoring mode; and for nine metals using conventional microwave-assisted acid digestion combined with ICP/MS.ResultsThe methods agreed in detecting the presence of the compounds 77% to 100% of the time (median 95%). For compounds with less than 100% agreement, neither method was consistently more sensitive than the other. Median concentrations were similar for most analytes, and Spearman correlation coefficients were 0.60 or higher except for allethrin (0.15) and malathion (0.24), which were detected infrequently, and benzo(k)fluoranthene (0.55), benzo(a)pyrene (0.55), PCB 105 (0.54), PCB 118 (0.54), and PCB 138 (0.58). Assuming that the HVS3 method is the "gold standard," the extent to which the household vacuum cleaner method yields relative risk estimates closer to unity by increasing random measurement error varies by compound and depends on the method used to calculate relative risk.ConclusionThe household vacuum cleaner method appears to be a reasonable alternative to the HVS3 for detecting, ranking, and quantifying the concentrations of pesticides and other compounds in carpet dust.

Honey classification from semi-arid, Atlantic and transitional forest zones in Bahia, Brazil

In this study, samples of honey produced in three different regional climates in the southwest Bahia, Brazil (semi-arid, Atlantic and Transitional Forest Zones) were characterized on the basis of their mineral and trace elements, ash content and electrical conductivity. The metals were determined by atomic absorption spectrophotometry. The cluster and principal component analysis (PCA) methods were applied to the chemical concentration data in order to study the chemistry variables capable of promoting a characterization of the honey produced in each area. Cluster analysis and PCA distinguishes the different groups of honey samples corresponding to each region of the three geographical origins. The high correlation between electrical conductivity and Cu observed in honey samples from transitional forest zones suggested a coupling to the nutrient cycle, and can be attributed to use of copper compounds in coffee production, a major activity developed in all transitional forest zones.

Thermal-hydrodynamic modeling of laboratory tests on the interaction of NaNO3-NaOH fluids with sandstone rock at a deep radionuclide repository site

Thermal-hydrodynamic modeling was used to reproduce laboratory tests involving sandstone samples collected from a deep radionuclide repository site at the Siberia Chemical Plant, Seversk (Russia). Laboratory tests included injection of alkaline fluids into sandstone samples at 70°C. Some minerals were forced in the model to precipitate or dissolve, according to laboratory test results. Modeling results were compared with observed test data (mineral phase changes, transient concentration data at the outlet of a sample column). Reasonable agreement was obtained between calculated and measured mineral phases (Na-smectite and kaolinite precipitation; quartz, microcline, chlorite, and muscovite dissolution). After the cation exchange option used in the model, the most abundant secondary mineral generated was dawsonite, which corresponds to sodium carbonates observed in the sample after the injection test. Time-dependent chemical concentrations (transient chemical concentration data) at the outlet of the sample column were qualitatively matched to the data observed.

Exposure Elements in Oil Spill Risk and Natural Resource Damage Assessments: A Review

ABSTRACT The use of the ecological risk assessment (ERA) framework for assessing effects of oil spills is applicable to the injury assessment component of natural resource damage assessment (NRDA). Central to the ERA process is the assessment of exposure, the critical component linking the release of oil to the assessment of effects. Exposure of biological receptors to the toxic fractions of spilled oil, usually considered the polycyclic aromatic hydrocarbons (PAH), requires carefully designed and implemented assessment studies, which are periodically refocused on various environmental pathways and the various biological receptors of concern over the life history of an oil spill from initial release to recovery. As important is the detailed assessment of the exposure regime in the absence of a spill (i.e., the baseline or background exposure). A release of petroleum may not, in itself, equate to an effect on a natural resource. The presence of residual petroleum hydrocarbons does not imply either availability to living organisms or injury to a biological resource. Precise and accurate chemical concentration and compositional data for 2–6 ringed PAHs and alkylated homologues are the key toxicologically important chemical components that are central to the exposure assessment. These principles are illustrated in several oil spill case studies.

Enhanced detection of m-xylene using a preconcentrator with a chemiresistor sensor

Chemiresistor chemical microsensors are being investigated as a tool for environmental monitoring. These devices can provide real-time in situ chemical concentration data for solvent-contaminated sites of interest. Detection limits of an unaided chemiresistor, however, are typically in the range of 1/1000th of the saturated vapor pressure of a given analyte, which may not be sufficient for chemicals with high vapor pressures and low desired detection limits. Tests were conducted in this study to determine the response of a chemiresistor sensor to m-xylene with and without preconcentration. Results showed that by adding a microfabricated preconcentrator to a chemiresistor sensor, detection limits of m-xylene were decreased by more than two orders of magnitude, from 13.5 ppm to 61.8 ppb, without significantly increasing the complexity of the sensing system.

Development of databases for use in validation studies of probabilistic models of dietary exposure to food chemicals and nutrients

The data currently available in the European Union in terms of food consumption and of food chemical and nutrient concentration data present many hnitations when used for estimating intake. The most refined techniques currently available were used within the European Union FP5 Monte Carlo project to estimate, as accurately as possible, the intake of food additives, pesticide residues and nutrients. Databases of ‘true’ intakes of food additives (based on brand level food consumption records and additive concentration data), pesticide residues (based on duplicate diet studies) and nutrients (based on biomarker studies) have thus been generated. These kind of estimates are rarely repeatable because the databases generated and used to calculate them require an extraordinary expenditure of time and resources. The databases created served the purpose of estimating as accurately as possible ‘true’ chemical intakes for assessing the validity of additive, nutrient and pesticide probabilistic models.

The use of food consumption data in assessments of exposure to food chemicals including the application of probabilistic modelling.

Emphasis on public health and consumer protection, in combination with globalisation of the food market, has created a strong demand for exposure assessments of food chemicals. The food chemicals for which exposure assessments are required include food additives, pesticide residues, environmental contaminants, mycotoxins, novel food ingredients, packaging-material migrants, flavouring substances and nutrients. A wide range of methodologies exists for estimating exposure to food chemicals, and the method chosen for a particular exposure assessment is influenced by the nature of the chemical, the purpose of the assessment and the resources available. Sources of food consumption data currently used in exposure assessments range from food balance sheets to detailed food consumption surveys of individuals and duplicate-diet studies. The fitness-for-purpose of the data must be evaluated in the context of data quality and relevance to the assessment objective. Methods to combine the food consumption data with chemical concentration data may be deterministic or probabilistic. Deterministic methods estimate intakes of food chemicals that may occur in a population, but probabilistic methods provide the advantage of estimating the probability with which different levels of intake will occur. Probabilistic analysis permits the exposure assessor to model the variability (true heterogeneity) and uncertainty (lack of knowledge) that may exist in the exposure variables, including food consumption data, and thus to examine the full distribution of possible resulting exposures. Challenges for probabilistic modelling include the selection of appropriate modes of inputting food consumption data into the models.

Reducing Uncertainty in Site Characterization Using Bayes Monte Carlo Methods

A Bayesian uncertainty analysis approach is developed as a tool for assessing and reducing uncertainty in ground-water flow and chemical transport predictions. The method is illustrated for a site contaminated with chlorinated hydrocarbons. Uncertainty in source characterization, in chemical transport parameters, and in the assumed hydrogeologic structure was evaluated using engineering judgment and updated using observed field data. The updating approach using observed hydraulic head data was able to differentiate between reasonable and unreasonable hydraulic conductivity fields but could not differentiate between alternative conceptual models for the geological structure of the subsurface at the site. Updating using observed chemical concentration data reduced the uncertainty in most parameters and reduced uncertainty in alternative conceptual models describing the geological structure at the site, source locations, and the chemicals released at these sources. Thirty-year transport projections for no-action and source containment scenarios demonstrate a typical application of the methods.

Growth and Contaminant Dynamics of Lake Superior Lake Trout

Lean lake trout ( Salvelinus namaycush) and the endemic siscowet are ecologically distinct phenotypes of char inhabiting Lake Superior. To examine growth and contaminant concentration dynamics of these fishes, and to assess their utility as indicators of environmental contamination, length, weight, estimated age, and muscle tissue lipid and organochlorine (OC) chemical concentration data were analyzed. Lean lake trout grew faster in length and weight than siscowet. Siscowet muscle tissue lipid concentrations were on average greater than in lean lake trout and increased with length and age, while lean lake trout muscle tissue lipid concentrations decreased in larger, older fish. Polychlorinated biphenyls (PCBs) were the most often detected contaminant, found in 95% of the lean lake trout analyzed and 100% of the siscowets. PCBs attained the highest concentration of the OC compounds quantified, followed by p,p’-DDE, dieldrin, and trans-nonachlor, respectively. Siscowet had greater total concentrations of PCBs at length than lean lake trout, but siscowet and lean lake trout had similar concentrations of PCBs at age. Based on 1990s growth and contaminant data, it is estimated that an 88 cm total length (16-year-old) lean lake trout and a 62 cm total length (15-year-old) siscowet from Lake Superior will exceed the 2.0 mg/kg “Action Level” for total concentrations of PCBs set by the United States Food and Drug Administration. Study results show phenotypic differences in growth and contaminant dynamics between lean lake trout and siscowet, findings that may improve our understanding and management of Lake Superior's aquatic resources.

The potential for long-range transport of air-pollutants into Greece: a climatological analysis

A flow climatology using 5 years (1983–1987) of back trajectories has been created for the Aliartos meteorological–chemical station (Greece’s EMEP-station ϕ=38° 13′N, λ=23° 00′E) using the Air Resources Laboratory (ARL) trajectory model. Air mass back trajectories were analysed to quantify the contributions of major source areas to the air pollution concentration in the area of Greece. The trajectories were produced two times a day at the 850-hPa and 700-hPa pressure surface. The trajectories were classified and summarised in order to produce a long range trajectory climatology. The purpose of this paper is to use the above flow climatology to improve understanding to atmospheric transport pathways to Greece (and to the greater south-eastern area of Europe) and to evaluate the polluting potential of distant source regions outside the country. The limited chemical concentration data available from Aliartos are used to evaluate the conclusions reached from the flow climatology and emissions analysis. The results show that trajectories reach Greece from five major source areas: (i) Northwest Europe, (ii) west Europe, (iii) north Europe, (iv) Northwest Asia, and (v) Northwest Africa. Sector analysis of air pollution concentrations and emissions also showed that: (i) Most air pollutants transport from distances beyond 1800 km takes place, and the most probable source areas are the industrialised countries of Europe. (ii) Countries of west and north-central Europe emit the greater amounts of air pollutants (S and N). (iii) Sulphate and nitrate concentrations are similar among transport sectors.

Factors affecting two-dimensional dopant profiles obtained by transmission electron microscopy of etched p-n junctions in Si

Transmission electron microscopy (TEM) was used to characterize image contrast obtained from doping-dependent etching of p-n junctions in silicon. The local variations in crystal thickness give rise to the appearance of thickness fringes which may be interpreted as two-dimensional iso-concentration contours that map the dopant distribution. The samples used for the study consisted of solid source diffusions of boron into substrates of varying resistivities of both n- and p-type. The factors which affect the interpretation of dopant profiles obtained from selective chemical etching of cross section TEM samples is addressed. One-dimensional chemical dopant concentration data were derived from secondary ion mass spectroscopy and one-dimensional carrier concentration data were derived from spreading resistance profiling.

Size distributions of atmospheric trace elements at dye 3, Greenland — I. Distribution characteristics and dry deposition velocities

Cascade impactor samples were collected at Dye 3 on the south-central Greenland Ice Sheet during March 1989. The impactor was calibrated in the laboratory, and the resulting collection efficiency curves were used to derive the impactor response for use in a data inversion procedure. The impactor samples were chemically analysed by proton-induced X-ray emission (PIXE), and the chemical concentration data were used with the inversion procedure to generate smooth size distributions for 15 elements. Results show three distinct size distribution categories. The first category includes elements that mainly originate from gas to particle conversion, with a substantial fraction from anthropogenic combustion (S, Pb, Zn, Br and Ni). These elements exhibit a unimodal size distribution with geometric mean aerodynamic diameter close to 0.6 μm, although S and Zn show a weak second mode centered at about 2 μm. Elements in the second category (Ti, Si, Fe, Mn, Ca, K) exhibit bimodal size distributions, with geometric mean diameters for the two modes of 0.6 and 2 μm, respectively. These elements results from a variety of sources, including crustal erosion as well as combustion from natural and anthropogenic sources. For elements in the third category (Al, Cl, Na, Mg), most of the mass occurs in particle sizes above 1 μm. Their size distribution is generally unimodal, with the geometric mean aerodynamic diameter around 2 μm. These elements are most likely to be of crustal and/or marine origin. The best-fit size distributions were used with curves of dry deposition velocity vs aerodynamic particle diameter to estimate the overall dry deposition velocity expected from the entire distribution. The deposition velocities for S, Pb, Zn, Br and Ni are all very low, with values less than about 0.02 cm s −1 if hygroscopic growth in the humid layer is neglected. For the other elements, deposition velocities are in the range 0.2-0.7 cm s −1. For those distributions that are bimodal, the upper mode generally dominates deposition even when most of he airborne mass is associated with the lower modes, as in the case of S and Zn.

An Estimation of the Risk Associated with the Organic Constituents of Hazardous and Municipal Waste Landfill Leachates

Although restrictions on the landfilling of hazardous industrial wastes have greatly increased, most municipal wastes are still disposed of in soil lined pits that can readily leak contaminated leachates to the subsurface environment. Since municipal waste landfills are numerous and contain many of the same compounds as found in industrial wastes, it is essential to evaluate the risks to human health and the environment from exposure to ground water contaminated with municipal waste landfill leachate. The present study was undertaken to compile chemical constituent and concentration data and, also, to estimate the risk which would be associated with exposure to the organic pollutants found in leachate from industrial and municipal waste landfills. Toxic and cancer causing chemicals were found in the leachates from all 58 landfills for which data were available irrespective of the type of waste which they received. Although different groups of pollutants are found in the different landfills, the concentrations and toxicity are such that the leachate from some municipal waste landfills may cause as great a cancer risk as those from industrial waste landfills. The risk calculations based on suspect carcinogens only indicate that the estimated carcinogenic potency for the leachate from some municipal landfills may be similar to the carcinogenic potency for the leachate from the Love Canal landfill.

Distribution and chemistry of fine roots in a white spruce – subalpine fir stand in British Columbia: implications for management

The vertical distribution of fine-root biomass, its chemical content, and the vertical distribution of overstory root tips were measured in a mature white spruce – subalpine fir stand (Piceaglauca (Moench) Voss – Abieslasiocarpa (Hook.) Nutt.) growing on an infertile sandy soil near Prince George, British Columbia, during July and August, 1975. The study was part of a larger project which described the biomass and chemical content of the tree and minor vegetation. The objective of the project was to provide information on nutrient losses accompanying whole-tree logging and to estimate the possible consequences of such losses for future tree production. Questions concerning the magnitude of the soil nutrient capital available to the vegetation indicated the need for information on the exploitation of the soil by the roots. This paper reports the results of an investigation of the fine roots. Living fine roots (<6.4 mm) of overstory trees and understory plants were sampled separately from 11 soil pits to an average depth of 94 cm. Overstory fine-root biomass was estimated to be about 1870 kg/ha of which 67% was in the forest floor (LFH horizon) and the Ae horizon. The average combined depth of these two horizons was only 8.3 cm, but they contained 88% of the overstory root tips sampled. The 3.3-cm-thick forest floor alone contained half of the fine-root biomass and approximately 70% of the overstory root tips. Understory fine-root biomass was estimated to be about 7880 kg/ha of which 69% was in the forest floor and the Ae horizon. The concentrations of N, P, K, Ca, and Mg generally decreased with increasing depth, while Fe and Al exhibited the opposite pattern.The marked concentration of fine-root biomass and root tips in the forest floor is interpreted as reflecting the very low nutrient status of the mineral soil on the study site. The high value of fine-root biomass for understory vegetation results from the open structure of the stand and is thought to reflect the great importance of this vegetation in nutrient cycling on the study site. The biomass data, together with root chemical concentration data, are consistent with the hypothesis that the forest floor is the major source of several of the macronutrients for the vegetation on the site.

Oil Saturation Measurements at Brown and East Voss Tannehill Fields

The partitioning tracer method was used to measure in-situ oil saturation in the Glorieta formation of the Brownfield and in the Tannehill sand of the East Voss Tannehill Unit. Such measurements are needed to evaluate the economic potential of applying an enhanced oil recovery process. Results obtained with this method also are presented. Introduction The amount of oil present in a reservoir is needed to evaluate applications of enhanced oil recovery processes. The residual oil saturation near the wellbore can be determined from cores and logs, but such data can be biase by abnormally high pressure drops and accompanying saturation changes. To measure in-situ oil saturation away from the wellbore, we employed the partitioning tracer method developed and licensed by Exxon Production Research Co. Measurements were made in the Glorieta (dolomite) formation of the Brown field and in the Tannehill sand of the East Voss Tannehill Unit. Tomich et al. and Bragg et al. have described the partitioning tracer method for measuring residual oil partitioning tracer method for measuring residual oil saturation and the theory behind it. In brief, the over-all procedure consists of three parts: (1) laboratory tests at procedure consists of three parts:laboratory tests at reservoir conditions to determine the chemical partitioning coefficients and rate of hydrolysis of the ester used,a mini-test to check the validity of the reaction-rate measurement and reservoir parameters, andthe main test to determine the oil saturation. The mini-test follows the same procedure as the main test. The oil saturation found with the mini-test can be the same as that of the main test. However, as the names imply, the volume of the reservoir contacted is different in each test. The mini-test may show that some change should be made in the test procedure and incorporated in the main test. Test Procedure The oil saturation measurement in the field requires the following sequence of steps.A slug of water is injected. The first portion of the slug contains both an ester (such as propyl formate) and methanol. The next portion contains only methanol. The selection of the ester depends on reservoir temperature.The slug is kept in the formation for a selected period of time to hydrolyze part of the propyl formate, period of time to hydrolyze part of the propyl formate, forming propanol and formic acid.The well is placed on production and samples of the produced water are analyzed for the tracer chemicals. produced water are analyzed for the tracer chemicals.Injection and production profiles are run several times during the test to determine where the fluids are entering and leaving the wellbore. Such information is necessary to define the reservoir model.The chemical concentrations measured for methanol, propyl formate, and propanol are plotted as a function of production. Then, these are compared with chemical concentration values generated by a computer model of the test application developed from pertinent reservoir and fluid parameters. The residual oil saturation is obtained by the best fit between computed and measured chemical concentration data determined by trial-and-error. Laboratory experiments using crude oil and brine samples (preferably from the test well) determine the partitioning coefficients of the propyl formate and partitioning coefficients of the propyl formate and propanol at reservoir temperature and pressure. propanol at reservoir temperature and pressure. JPT P. 17