Weighted least-squares approach to calculating limits of detection and quantification by modeling variability as a function of concentration

Weighted Linear Regression Improves Accuracy of Quantitative Elemental Bioimaging by Means of LA-ICP-MS

The application of ordinary least squares (OLS) linear regression is widely used in order to approximate linear external calibration data. However, the assumption of homoscedasticity is often not considered as a requirement for correct data approximation, which can result in a poor regression fit that is often more prominent in the lower concentration range. Heteroscedasticity in inductively coupled plasma-mass spectrometry (ICP-MS) data has been discussed in literature as an intrinsic problem and was found to be addressed better by the use of weighted least squares (WLS) regression in multiple studies. In this study, the effects of OLS and WLS linear regression models have been investigated for quantitative imaging experiments by means of laser ablation (LA)-ICP-MS using matrix-matched standards. The calibration data produced by this technique was found to be heteroscedastic in all 60 analyzed datasets, which yielded poor regression fits for OLS linear regression. In comparison to conventional ICP-MS analysis, the resulting negative effects were found to become even more visible in imaging LA-ICP-MS due to an inaccurate estimation of the regression line's intercept. Also, the calculation of average concentrations in selected regions of interest (ROIs) yields incorrect quantification results at the lower end of the calibration range. The application of WLS linear regression resulted in an improved goodness of fit (GOF), although the weighting factor should be selected carefully. Besides the reciprocal of the variance of each calibration standard (1/s_i²), more empirical weighting factors that have been discussed in the literature were also evaluated regarding the GOF.

The inadequate use of the determination coefficient in analytical calibrations: How other parameters can assess the goodness-of-fit more adequately

Simple linear regression using ordinary least-squares is the most common function applied in laboratories for analytical calibrations. The determination and/or the correlation coefficients are usually the parameters applied for assessing the goodness-of-fit of a simple linear calibration. However, these parameters are unable to detect the highly biased results at low calibration levels that are obtained with ordinary least-squares. In this study, the use of other parameters based on the relative standard errors of the calculated contents is evaluated. It has been found that these alternative parameters can detect the biased results obtained at low calibration levels with ordinary least-squares, being the relative standard error the one that seems to provide the most adequate results. Ordinary least-squares should only be applied if the lower limit of quantification is set to at least five times above the conventional limit of quantification. For trace analysis, where the lowest possible limit of quantification is required, weighted least-squares should be applied to obtain accurate estimates, especially at low concentrations. One of the greatest advantages of the relative standard error is that this parameter can be determined for all types of regression functions and is not limited to calibrations with linear relationships between the variables.

Rapid self-disassembly of DNA diblock copolymer micelles via target induced hydrophilic-hydrophobic regulation for sensitive MiRNA detection

In this work, a novel DNA nanostructure with a shorter assembly time and larger loading capacity was constructed using amphiphilic DNA-alkane group (Spacer C12)₁₀ conjugates encapsulating plentiful fat-soluble fluorescent dyes into the hydrophobic core to form the DNA micelles, which could be rapidly self-disassembled via target induced hydrophilic-hydrophobic regulation to release fluorescent dyes from micelles to the organic phase, realizing the fast and sensitive detection of microRNA.

Linear calibrations in chromatography: The incorrect use of ordinary least squares for determinations at low levels, and the need to redefine the limit of quantification with this regression model

Ordinary least squares is widely applied as the standard regression method for analytical calibrations, and it is usually accepted that this regression method can be used for quantification starting at the limit of quantification. However, it requires calibration being homoscedastic and this is not common. Different calibrations have been evaluated to assess whether ordinary least squares is adequate to quantify estimates at low levels. All calibrations evaluated were linear and heteroscedastic. Despite acceptable values for precision at limit of quantification levels were obtained, ordinary least squares fitting resulted in significant and unacceptable bias at low levels. When weighted least squares regression was applied, bias at low levels was solved and accurate estimates were obtained. With heteroscedastic calibrations, limit values determined by conventional methods are only appropriate if weighted least squares are used. A "practical limit of quantification" can be determined with ordinary least squares in heteroscedastic calibrations, which should be fixed at a minimum of 20 times the value calculated with conventional methods. Biases obtained above this "practical limit" were acceptable applying ordinary least squares and no significant differences were obtained between the estimates measured using weighted and ordinary least squares when analyzing real-world samples.

Biomimetic 3D DNA Nanomachine via Free DNA Walker Movement on Lipid Bilayers Supported by Hard SiO2@CdTe Nanoparticles for Ultrasensitive MicroRNA Detection

Herein, a novel three-dimensional (3D) DNA nanomachine with high walking efficiency via free DNA walker movement on biomimetic lipid bilayers supported by hard silica@CdTe quantum dots (SiO₂@CdTe) was constructed for ultrasensitive fluorescence detection of microRNA. The synthesized SiO₂@CdTe nanoparticles were adopted as the fluorescence indicator and spherical carrier of lipid bilayers, and then the DNA substrates were anchored on lipid bilayers with biomimetic fluidity through the cholesterol-lipid interaction. Once target microRNA-141 interacted with the 3D DNA nanomachine to release cholesterol labeled arm (Chol-arm), the Chol-arm could generate a series of strand displacement reactions by moving freely on the lipid bilayers, resulting in the releasement of numerous quenchers from the SiO₂@CdTe nanoparticles and inducing a strong fluorescence signal. Impressively, compared with traditional 3D DNA nanomachine conjugating DNA substrates on hard surfaces (such as gold or silica) with limited reactivity, the proposed biomimetic 3D DNA nanomachine not only immobilized DNA substrates rapidly and effectively but also kept it with a favorable fluidity, which significantly enhanced the walking efficiency. As expected, the biomimetic 3D DNA nanomachine for fluorescence detection of microRNA-141 exhibited an excellent performance with a detection limit of 0.21 pM and presented promising properties in cell lysate detection and intracellular imaging. Thus, the described biomimetic 3D DNA nanomachine provided a novel avenue for sensitive detection of biomolecules, which could be useful for bioanalysis and early clinical diagnoses of disease.

Achieving confidence in trace element analysis for nuclear forensic purposes: ICP-MS measurements using external calibration

In this work, problems arising from performing trace element analysis using inductively coupled plasma—mass spectrometry with low measurement uncertainties are addressed. It is shown that some reference materials certified for massic concentration of lanthanides may have either deviating concentrations or underestimated measurement uncertainties. It is also shown that the choice of methods for sample preparation and linear regression to perform external calibration is affecting the outcome of the measurement results and their uncertainties. The results show that, from the selection of methods investigated in this work, the lowest measurement uncertainties can be achieved by using weighted linear regression to evaluate the calibration function and gravimetric dilutions of samples.

Calibration: Detection, Quantification, and Confidence Limits Are (Almost) Exact When the Data Variance Function Is Known

Inverse variance weighting ensures optimal parameter estimation in least-squares fitting, with exact parameter standard errors for linear least-squares with known data variance. In this Feature, I emphasize the virtues of numerical methods for estimating data variance functions and for determining these limits for any calibration model, linear or nonlinear.

Estimating Detection Limits in Chromatography from Calibration Data: Ordinary Least Squares Regression vs. Weighted Least Squares

It is necessary to determine the limit of detection when validating any analytical method. For methods with a linear response, a simple and low labor-consuming procedure is to use the linear regression parameters obtained in the calibration to estimate the blank standard deviation from the residual standard deviation (sres), or the intercept standard deviation (sb0). In this study, multiple experimental calibrations are evaluated, applying both ordinary and weighted least squares. Moreover, the analyses of replicated blank matrices, spiked at 2–5 times the lowest calculated limit values with the two regression methods, are performed to obtain the standard deviation of the blank. The limits of detection obtained with ordinary least squares, weighted least squares, the signal-to-noise ratio, and replicate blank measurements are then compared. Ordinary least squares, which is the simplest and most commonly applied calibration regression methodology, always overestimate the values of the standard deviations at the lower levels of calibration ranges. As a result, the detection limits are up to one order of magnitude greater than those obtained with the other approaches studied, which all gave similar limits.

Nonlinear Regression Improves Accuracy of Characterization of Multiplexed Mass Spectrometric Assays

The need for assay characterization is ubiquitous in quantitative mass spectrometry-based proteomics. Among many assay characteristics, the limit of blank (LOB) and limit of detection (LOD) are two particularly useful figures of merit. LOB and LOD are determined by repeatedly quantifying the observed intensities of peptides in samples with known peptide concentrations and deriving an intensity versus concentration response curve. Most commonly, a weighted linear or logistic curve is fit to the intensity-concentration response, and LOB and LOD are estimated from the fit. Here we argue that these methods inaccurately characterize assays where observed intensities level off at low concentrations, which is a common situation in multiplexed systems. This manuscript illustrates the deficiencies of these methods, and proposes an alternative approach based on nonlinear regression that overcomes these inaccuracies. We evaluated the performance of the proposed method using computer simulations and using eleven experimental data sets acquired in Data-Independent Acquisition (DIA), Parallel Reaction Monitoring (PRM), and Selected Reaction Monitoring (SRM) mode. When the intensity levels off at low concentrations, the nonlinear model changes the estimates of LOB/LOD upwards, in some data sets by 20-40%. In absence of a low concentration intensity leveling off, the estimates of LOB/LOD obtained with nonlinear statistical modeling were identical to those of weighted linear regression. We implemented the nonlinear regression approach in the open-source R-based software MSstats, and advocate its general use for characterization of mass spectrometry-based assays.

A single-source photon source model of a linear accelerator for Monte Carlo dose calculation

PURPOSE

To introduce a new method of deriving a virtual source model (VSM) of a linear accelerator photon beam from a phase space file (PSF) for Monte Carlo (MC) dose calculation.

MATERIALS AND METHODS

A PSF of a 6 MV photon beam was generated by simulating the interactions of primary electrons with the relevant geometries of a Synergy linear accelerator (Elekta AB, Stockholm, Sweden) and recording the particles that reach a plane 16 cm downstream the electron source. Probability distribution functions (PDFs) for particle positions and energies were derived from the analysis of the PSF. These PDFs were implemented in the VSM using inverse transform sampling. To model particle directions, the phase space plane was divided into a regular square grid. Each element of the grid corresponds to an area of 1 mm2 in the phase space plane. The average direction cosines, Pearson correlation coefficient (PCC) between photon energies and their direction cosines, as well as the PCC between the direction cosines were calculated for each grid element. Weighted polynomial surfaces were then fitted to these 2D data. The weights are used to correct for heteroscedasticity across the phase space bins. The directions of the particles created by the VSM were calculated from these fitted functions. The VSM was validated against the PSF by comparing the doses calculated by the two methods for different square field sizes. The comparisons were performed with profile and gamma analyses.

RESULTS

The doses calculated with the PSF and VSM agree to within 3% /1 mm (>95% pixel pass rate) for the evaluated fields.

CONCLUSION

A new method of deriving a virtual photon source model of a linear accelerator from a PSF file for MC dose calculation was developed. Validation results show that the doses calculated with the VSM and the PSF agree to within 3% /1 mm.

COMPARISON OF DIFFERENT PADC MATERIALS AND ETCHING CONDITIONS FOR FAST NEUTRON DOSIMETRY

Etched-track polyallyl diglycol carbonate (PADC) dosemeters have been in use at the Paul Scherrer Institute since 1998 in neutron dosimetry for individual monitoring. In the last years, the availability of PADC materials from different manufacturers has grown, and different etching conditions were proposed, with the intention to improve the quality and overall performance of PADC in individual neutron monitoring. The goal of the present study was to compare the performance of different PADC materials and to investigate the influence of different etching conditions on sensitivity to fast neutrons and lower detection limit. The comparison covers six different PADC materials and eight different etching conditions.

Comparative toxicity of pyrethroid insecticides to two estuarine crustacean species, Americamysis bahia and Palaemonetes pugio

Pyrethroid insecticides are widely used on agricultural crops, as well as for nurseries, golf courses, urban structural and landscaping sites, residential home and garden pest control, and mosquito abatement. Evaluation of sensitive marine and estuarine species is essential for the development of toxicity testing and risk-assessment protocols. Two estuarine crustacean species, Americamysis bahia (mysids) and Palaemonetes pugio (grass shrimp), were tested with the commonly used pyrethroid compounds, lambda-cyhalothrin, permethrin, cypermethrin, deltamethrin, and phenothrin. Sensitivities of adult and larval grass shrimp and 7-day-old mysids were compared using standard 96-h LC50 bioassay protocols. Adult and larval grass shrimp were more sensitive than the mysids to all the pyrethroids tested. Larval grass shrimp were approximately 18-fold more sensitive to lambda-cyhalothrin than the mysids. Larval grass shrimp were similar in sensitivity to adult grass shrimp for cypermethrin, deltamethrin, and phenothrin, but larvae were approximately twice as sensitive to lambda-cyhalothrin and permethrin as adult shrimp. Acute toxicity to estuarine crustaceans occurred at low nanogram per liter concentrations of some pyrethroids, illustrating the need for careful regulation of the use of pyrethroid compounds in the coastal zone.

Laboratory estimation of net trophic transfer efficiencies of PCB Congeners to lake trout (Salvelinus namaycush) from its prey

A technique for laboratory estimation of net trophic transfer efficiency (γ) of polychlorinated biphenyl (PCB) congeners to piscivorous fish from their prey is described herein. During a 135-day laboratory experiment, we fed bloater (Coregonus hoyi) that had been caught in Lake Michigan to lake trout (Salvelinus namaycush) kept in eight laboratory tanks. Bloater is a natural prey for lake trout. In four of the tanks, a relatively high flow rate was used to ensure relatively high activity by the lake trout, whereas a low flow rate was used in the other four tanks, allowing for low lake trout activity. On a tank-by-tank basis, the amount of food eaten by the lake trout on each day of the experiment was recorded. Each lake trout was weighed at the start and end of the experiment. Four to nine lake trout from each of the eight tanks were sacrificed at the start of the experiment, and all 10 lake trout remaining in each of the tanks were euthanized at the end of the experiment. We determined concentrations of 75 PCB congeners in the lake trout at the start of the experiment, in the lake trout at the end of the experiment, and in bloaters fed to the lake trout during the experiment. Based on these measurements, γ was calculated for each of 75 PCB congeners in each of the eight tanks. Mean γ was calculated for each of the 75 PCB congeners for both active and inactive lake trout. Because the experiment was replicated in eight tanks, the standard error about mean γ could be estimated. Results from this type of experiment are useful in risk assessment models to predict future risk to humans and wildlife eating contaminated fish under various scenarios of environmental contamination.

EPR dosimetry intercomparison using smart phone touch screen glass

This paper presents the results of an interlaboratory comparison of retrospective dosimetry using the electron paramagnetic resonance method. The test material used in this exercise was glass coming from the touch screens of smart phones that might be used as fortuitous dosimeters in a large-scale radiological incident. There were 13 participants to whom samples were dispatched, and 11 laboratories reported results. The participants received five calibration samples (0, 0.8, 2, 4, and 10 Gy) and four blindly irradiated samples (0, 0.9, 1.3, and 3.3 Gy). Participants were divided into two groups: for group A (formed by three participants), samples came from a homogeneous batch of glass and were stored in similar setting; for group B (formed by eight participants), samples came from different smart phones and stored in different settings of light and temperature. The calibration curves determined by the participants of group A had a small error and a critical level in the 0.37-0.40-Gy dose range, whereas the curves determined by the participants of group B were more scattered and led to a critical level in the 1.3-3.2-Gy dose range for six participants out of eight. Group A were able to assess the dose within 20 % for the lowest doses (<1.5 Gy) and within 5 % for the highest doses. For group B, only the highest blind dose could be evaluated in a reliable way because of the high critical values involved. The results from group A are encouraging, whereas the results from group B suggest that the influence of environmental conditions and the intervariability of samples coming from different smart phones need to be further investigated. An alongside conclusion is that the protocol was easily transferred to participants making a network of laboratories in case of a mass casualty event potentially feasible.

Assessing the detection capacity of microarrays as bio/nanosensing platforms

Microarray is one of the most powerful detection systems with multiplexing and high throughput capability. It has significant potential as a versatile biosensing platform for environmental monitoring, pathogen detection, medical therapeutics, and drug screening to name a few. To date, however, microarray applications are still limited to preliminary screening of genome-scale transcription profiling or gene ontology analysis. Expanding the utility of microarrays as a detection tool for various biological and biomedical applications requires information about performance such as the limits of detection and quantification, which are considered as an essential information to decide the detection sensitivity of sensing devices. Here we present a calibration design that integrates detection limit theory and linear dynamic range to obtain a performance index of microarray detection platform using oligonucleotide arrays as a model system. Two different types of limits of detection and quantification are proposed by the prediction or tolerance interval for two common cyanine fluorescence dyes, Cy3 and Cy5. Besides oligonucleotide, the proposed method can be generalized to other microarray formats with various biomolecules such as complementary DNA, protein, peptide, carbohydrate, tissue, or other small biomolecules. Also, it can be easily applied to other fluorescence dyes for further dye chemistry improvement.

Screening biological stains with qPCR versus lateral flow immunochromatographic test strips: a quantitative comparison using analytical figures of merit

Biological fluid identification is an important facet of evidence examination in forensic laboratories worldwide. While identifying bodily fluids may provide insight into which downstream DNA methods to employ, these screening techniques consume a vital portion of the available evidence, are usually qualitative, and rely on visual interpretation. In contrast, qPCR yields information regarding the amount and proportion of amplifiable genetic material. In this study, dilution series of either semen or male saliva were prepared in either buffer or female blood. The samples were subjected to both lateral flow immunochromatographic test strips and qPCR analysis. Analytical figures of merit-including sensitivity, minimum distinguishable signal (MDS) and limit of detection (LOD)-were calculated and compared between methods. By applying the theory of the propagation of random errors, LODs were determined to be 0.05 μL of saliva for the RSID™ Saliva cards, 0.03 μL of saliva for Quantifiler(®) Duo, and 0.001 μL of semen for Quantifiler(®) Duo. In conclusion, quantitative PCR was deemed a viable and effective screening method for subsequent DNA profiling due to its stability in different matrices, sensitivity, and low limits of detection.

Antifouling biocides in water and sediments from California marinas

Irgarol 1051 is a common antifouling biocide and is highly toxic to non-target plant species at low ng/L concentrations. We measured up to 254 ng/L Irgarol in water and up to 9 ng/g dry weight Irgarol in sediments from Southern California recreational marinas. Irgarol's metabolite, M1, concentrations were up to 62 ng/L in water and 5 ng/g dry weight in sediments. Another antifouling biocide, diuron, reached up to 68 ng/L in water and 4 ng/g dry weight in sediments. The maximum Irgarol concentrations in water were greater than the Irgarol concentration recommended as the plant toxicity benchmark (136 ng/L), suggesting that Irgarol concentrations may be high enough to cause changes in phytoplankton communities in the sampled marinas. Irgarol concentrations measured in sediments were greater than calculated Environmental Risk Limits (ERLs) for Irgarol in sediments (1.4 ng/g). Antifouling pesticide accumulation in sediments may present a potential undetermined risk for benthic organisms.

Net trophic transfer efficiencies of polychlorinated biphenyl congeners to lake trout (Salvelinus namaycush) from its prey

Lake trout (Salvelinus namaycush) were fed bloater (Coregonus hoyi) in eight laboratory tanks over a 135-d experiment. At the start of the experiment, four to nine fish in each tank were sacrificed, and the concentrations of 75 polychlorinated biphenyl (PCB) congeners within these fish were determined. Polychlorinated biphenyl congener concentrations were also determined in the 10 lake trout remaining in each of the eight tanks at the end of the experiment as well as in the bloater fed to the lake trout. Each lake trout was weighed at the start and the end of the experiment, and the amount of food eaten by the lake trout was recorded. Using these measurements, net trophic transfer efficiency (γ) from the bloater to the lake trout in each of the eight tanks was calculated for each of the 75 congeners. Results showed that γ did not vary significantly with the degree of chlorination of the PCB congeners, and γ averaged 0.66 across all congeners. However, γ did show a slight, but significant, decrease as log K(OW) increased from 6.0 to 8.2. Activity level of the lake trout did not have a significant effect on γ.

Interlaboratory evaluation of automated, multiplexed peptide immunoaffinity enrichment coupled to multiple reaction monitoring mass spectrometry for quantifying proteins in plasma

The inability to quantify large numbers of proteins in tissues and biofluids with high precision, sensitivity, and throughput is a major bottleneck in biomarker studies. We previously demonstrated that coupling immunoaffinity enrichment using anti-peptide antibodies (SISCAPA) to multiple reaction monitoring mass spectrometry (MRM-MS) produces Immunoprecipitation MRM-MS (immuno-MRM-MS) assays that can be multiplexed to quantify proteins in plasma with high sensitivity, specificity, and precision. Here we report the first systematic evaluation of the interlaboratory performance of multiplexed (8-plex) immuno-MRM-MS in three independent labs. A staged study was carried out in which the effect of each processing and analysis step on assay coefficient of variance, limit of detection, limit of quantification, and recovery was evaluated. Limits of detection were at or below 1 ng/ml for the assayed proteins in 30 μl of plasma. Assay reproducibility was acceptable for verification studies, with median intra- and interlaboratory coefficients of variance above the limit of quantification of 11% and <14%, respectively, for the entire immuno-MRM-MS assay process, including enzymatic digestion of plasma. Trypsin digestion and its requisite sample handling contributed the most to assay variability and reduced the recovery of target peptides from digested proteins. Using a stable isotope-labeled protein as an internal standard instead of stable isotope-labeled peptides to account for losses in the digestion process nearly doubled assay accuracy for this while improving assay precision 5%. Our results demonstrate that multiplexed immuno-MRM-MS can be made reproducible across independent laboratories and has the potential to be adopted widely for assaying proteins in matrices as complex as plasma.

Sensitive and accurate quantification of human leukocyte migration using high-content Discovery-1 imaging system and ATPlite assay

Migration is a fundamental aspect of leukocyte behavior and represents a significant therapeutic target clinically. However, most migration assays used in research are relatively low throughput and not easily compatible with rapid analysis or high-throughput screening (HTS) protocols required for drug screening assays. We therefore investigated the quantification of the migration of human leukocytes using the Molecular Devices high-content Discovery-1 platform or PerkinElmer ATPlite assay compared to manual counting. We have conducted extensive assay validation, investigating the detection limits, sensitivity, and precision of each method to count human leukocytes. Leukocyte migration assays were conducted using 96-well HTS-Transwell plates and the potent chemokine stromal cell-derived factor-1 (SDF-1). We reveal that the Discovery-1 and ATPlite methods developed here provide useful approaches to quantify leukocyte migration in an HTS manner with high levels of detection, sensitivity, and precision.

Theil-Sen nonparametric regression technique on univariate calibration, inverse regression and detection limits

This paper reports the combined use of the nonparametric Theil-Sen (TS) regression technique and of the statistics of Lancaster-Quade (LQ) concerning the linear regression parameters to solve typical analytical problems, like method comparison, calculation of the uncertainty in the inverse regression, determination of the detection limit. The results of this new approach are compared to those obtained with appropriate reference methods, using simulated and real data sets. The nonparametric Theil-Sen regression technique appears a new robust tool for the problems considered because it is free from restrictive statistical constraints, avoids searching for the error nature on x and y, which may require long analysis times, and it is easy to use. The only drawback is that the intrinsic nature of the method may lead to a possible enlargement of the uncertainty interval of the discriminated concentration and to the determination of larger detection limits than those obtainable with the commonly used, less robust, regression techniques.

Selected reaction monitoring applied to proteomics

Selected reaction monitoring (SRM) performed on triple quadrupole mass spectrometers has been the reference quantitative technique to analyze small molecules for several decades. It is now emerging in proteomics as the ideal tool to complement shotgun qualitative studies; targeted SRM quantitative analysis offers high selectivity, sensitivity and a wide dynamic range. However, SRM applied to proteomics presents singularities that distinguish it from small molecules analysis. This review is an overview of SRM technology and describes the specificities and the technical aspects of proteomics experiments. Ongoing developments aiming at increasing multiplexing capabilities of SRM are discussed; they dramatically improve its throughput and extend its field of application to directed or supervised discovery experiments.

Contaminant blubber burdens in Atlantic bottlenose dolphins (Tursiops truncatus) from two southeastern US estuarine areas: concentrations and patterns of PCBs, pesticides, PBDEs, PFCs, and PAHs

Polychlorinated biphenyls (PCBs), chlorinated pesticides (i.e., dichlorodiphenyltrichloroethane (DDT) and its metabolites, chlordanes (CHLs), dieldrin, hexachlorobenzene (HCB), and mirex), polybrominated diphenyl ethers (PBDEs), perfluorinated chemicals (PFCs), and polyaromatic hydrocarbons (PAHs) were measured in blubber biopsy samples collected from 139 wild bottlenose dolphins (Tursiops truncatus) during 2003-2005 in Charleston (CHS), SC and the Indian River Lagoon (IRL), FL. Dolphins accumulated a similar suite of contaminants with summation operatorPCB dominating (CHS 64%, IRL 72%), followed by summation operatorDDT (CHS 20%, IRL 17%), summation operatorCHLs (CHS 7%; IRL 7%), summation operatorPBDE (CHS 4%, IRL 2%), PAH at 2%, and dieldrin, PFCs and mirex each 1% or less. Together summation operatorPCB and summation operatorDDT concentrations contributed approximately 87% of the total POCs measured in blubber of adult males. summation operatorPCBs in adult male dolphins exceed the established PCB threshold of 17mg/kg by a 5-fold order of magnitude with a 15-fold increase for many animals; 88% of the dolphins exceed this threshold. For male dolphins, CHS (93,980ng/g lipid) had a higher summation operatorPCBs geomean compared to the IRL (79,752ng/g lipid) although not statistically different. In adult males, the PBDE geometric mean concentration was significantly higher in CHS (5920ng/g lipid) than the IRL (1487ng/g). Blubber summation operatorPFCs concentrations were significantly higher in CHS dolphins. In addition to differences in concentration of PCB congeners, summation operatorPBDE, TEQ, summation operatorCHLs, mirex, dieldrin, and the ratios summation operatorDDE/ summation operatorDDT and trans-nonachlor/cis-nonachlor were the most informative for discriminating contaminant loads in these two dolphin populations. Collectively, the current summation operatorPCB, summation operatorDDT, and summation operatorPBDEs blubber concentrations found in CHS dolphins are among the highest reported values in marine mammals. Both dolphin populations, particularly those in CHS, carry a suite of organic chemicals at or above the level where adverse effects have been reported in wildlife, humans, and laboratory animals warranting further examination of the potential adverse effects of these exposures.

Multi-site assessment of the precision and reproducibility of multiple reaction monitoring-based measurements of proteins in plasma

Verification of candidate biomarkers relies upon specific, quantitative assays optimized for selective detection of target proteins, and is increasingly viewed as a critical step in the discovery pipeline that bridges unbiased biomarker discovery to preclinical validation. Although individual laboratories have demonstrated that multiple reaction monitoring (MRM) coupled with isotope dilution mass spectrometry can quantify candidate protein biomarkers in plasma, reproducibility and transferability of these assays between laboratories have not been demonstrated. We describe a multilaboratory study to assess reproducibility, recovery, linear dynamic range and limits of detection and quantification of multiplexed, MRM-based assays, conducted by NCI-CPTAC. Using common materials and standardized protocols, we demonstrate that these assays can be highly reproducible within and across laboratories and instrument platforms, and are sensitive to low mug/ml protein concentrations in unfractionated plasma. We provide data and benchmarks against which individual laboratories can compare their performance and evaluate new technologies for biomarker verification in plasma.

Effects of fluoxetine exposure on serotonin-related activity in the sheepshead minnow (Cyprinodon variegatus) using LC/MS/MS detection and quantitation

Fluoxetine (FLX) is a selective serotonin reuptake inhibitor and is among the top 100 drugs prescribed yearly in the United States and the United Kingdom. Tissue and water extraction methods were developed to detect and quantify FLX, norfluoxetine and the associated biological compounds serotonin (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophan (TRP) and melatonin (MEL) using LC/MS/MS. Acute mortality and sublethal physiological effects of FLX were assessed using standard static renewal toxicity tests in which juvenile sheepshead minnows (Cyprinodon variegatus) were exposed to FLX. Fluoxetine did not cause significant mortality at levels near currently reported environmental concentrations. Significant changes in neurotransmitter levels were observed within the serotonergic system in juvenile sheepshead minnows exposed at concentrations approximately one order of magnitude above those currently reported in the environment. Transformation activity ratios of a product to a precursor compound (5-HT/TRP, 5-HIAA/5-HT and MEL/5-HT) also exhibited significant changes with FLX treatment. Fluoxetine exposure did not only affect 5-HT but had additional effects both upstream and downstream of 5-HT within its synthesis and metabolic pathways. These sublethal changes within the serotonergic pathway may result in behavioral changes which could, in turn, have implications for the ecological response of populations to additional environmental stressors.

Lethal and sublethal effects of the pyrethroid, bifenthrin, on grass shrimp (Palaemonetes pugio) and sheepshead minnow (Cyprinodon variegatus)

This study investigated the lethal and sublethal effects of the pyrethroid insecticide bifenthrin on adult and larval grass shrimp, Palaemonetes pugio, and adult sheepshead minnows, Cyprinodon variegatus. The effects were determined by conducting 96-h aqueous static renewal tests and 24-h static tests with sediment. Oxidative stress biomarkers, lipid peroxidation, glutathione, and catalase were also assessed. The 96-h aqueous LC50 value for adult shrimp was 0.020 microg/L (95% CI: 0.015-0.025 microg/L) and for larval shrimp was 0.013 microg/L (95% CI: 0.011-0.016 microg/L). The 96-h aqueous LC50 for adult sheepshead minnow was 19.806 microg/L (95% CI: 11.886-47.250 microg/L). The 24-h sediment LC50 for adult shrimp was 0.339 microg/L (95% CI: 0.291-0.381 microg/L) and for larval shrimp was 0.210 microg/L (95% CI: 0.096-0.393 microg/L). The oxidative stress assays showed some increasing trends toward physiological stress with increased bifenthrin concentrations but they were largely inconclusive. Given the sensitivity of grass shrimp to this compound in laboratory bioassays, additional work will be needed to determine if these exposure levels are environmentally relevant.

Effects of the anti-fouling herbicide Irgarol 1051 on two life stages of the grass shrimp, Palaemonetes pugio

This study investigated lethal and sublethal effects (glutathione, lipid peroxidation, cholesterol, and acetylcholinesterase) of the anti-fouling herbicide Irgarol 1051 on larval and adult grass shrimp (Palaemonetes pugio). The 96-hour LC50 test for larvae resulted in an estimated LC50 of 1.52 mg/L (95% confidence interval [CI] 1.26-1.85 mg/L). The adult 96-h LC50 was 2.46 mg/L (95% CI = 2.07-2.93 mg/L). Glutathione, lipid peroxidation, cholesterol and acetylcholinesterase levels were not significantly affected in adult grass shrimp by exposure of up to 3.00 mg/L irgarol. Lipid peroxidation and acetylcholinesterase levels in the larvae were significantly higher than controls in the highest irgarol exposures of 1.0 and 2.0 mg/L, respectively. Cholesterol levels were significantly reduced in larvae in all four irgarol concentrations tested while glutathione levels were not significantly affected in larvae. Both lethal and sublethal effects associated with irgarol exposure were only observed at concentrations well above those reported in the environment.