Inter-laboratory Calibration Exercise Research Articles

How to establish detection limits for environmental microplastics analysis

Establishing analytical detection limits is crucial. Common methods to do so are suitable only for variables with continuous distributions. Because count data for microplastic particles is a discrete variable following the Poisson distribution, currently-used approaches for estimating the detection limit in microplastics analysis are inadequate. Here we evaluate detection limits with techniques for low-level discrete observations to develop proper approaches for estimating the minimum detectable amount (MDA) in microplastic particle analysis, using blank sample data from an interlaboratory calibration exercise for clean water (representing drinking water), dirty water (ambient water), sediment (porous media) and fish tissue (biotic tissues). Two MDAs are applicable: MDAA to evaluate analytical methods, estimated with replicate blank data; and MDAB for individual sample batches, calculated with a single blank count. For illustrative purposes, this dataset's overall MDAA values were 164 counts (clean water), 88 (dirty water), 192 (sediment), and 379 (tissue). MDA values should be reported on a laboratory-specific basis and for individual size fractions, as this provides more useful information about capabilities of individual laboratories. This is due to wide variation in blank levels, as noted by MDAB values (i.e., among different laboratories) from 14 to 158 (clean water), 9 to 86 (dirty water, 9 to 186 (sediment), and 9 to 247 (tissue). MDA values for fibers were considerably greater than for non-fibers, suggesting that separate MDA values should be reported. This study provides a guideline for estimation and application of microplastics MDA for more robust data to support research activities and environmental management decisions.

A bone to pick with age estimation using hard parts: A case study of swordfish, Xiphias gladius, in the southwest Pacific Ocean

Life history parameters of fish can vary spatially, and these differences have been used to identify separate stocks for management. However, inconsistency in the methods used to obtain the parameters is often overlooked as a possible explanation for the variability in parameters. Here, we sought to understand whether large differences in growth parameters obtained for broadbill swordfish (Xiphias gladius) in the southwest Pacific Ocean and central Pacific Ocean were due to methodological differences in estimating age, and to evaluate the most appropriate hard part for providing annual age estimates. Sectioned anal fin rays were obtained from an earlier study undertaken in the southwest Pacific (1995–2003) and the assumed annuli were re-counted for a subset, using criteria confirmed through an inter-laboratory calibration exercise. Sagittal otoliths were also obtained from the same study (in which otoliths had been collected but annual age had not been estimated) and the assumed annuli present in transversely sectioned otoliths were counted using new criteria for reading growth zones. Ray-based growth curves were different to the curves obtained in the original 1995–2003 study, confirming that methodological differences exist among studies that use fin rays in the Pacific. More importantly, a direct comparison of the new age estimates from fin rays and otoliths showed a clear bias; ray age was lower on average than otolith age for females > 7 years and males > 4 years. Considering that otoliths have been shown to be more reliable than alternative hard parts for estimating the age and longevity for many species, the results suggest that swordfish live longer and grow more slowly than previously estimated in the Pacific. A maximum age of 21 years was obtained from otoliths and 14 years from rays. We recommend that protocols are established to ensure that hard part reading methods are standardised among laboratories and that otolith-based age estimation is investigated and validated for all billfish stocks, and potentially other fish species.

Validation of a two-generational reproduction test in Daphnia magna: An interlaboratory exercise.

Effects observed within one generation disregard potential detrimental effects that may appear across generations. Previously we have developed a two generation Daphnia magna reproduction test using the OECD TG 211 protocol with a few amendments, including initiating the second generation with third brood neonates produced from first generation individuals. Here we showed the results of an inter-laboratory calibration exercise among 12 partners that aimed to test the robustness and consistency of a two generation Daphnia magna reproduction test. Pyperonyl butoxide (PBO) was used as a test compound. Following experiments, PBO residues were determined by TQD-LC/MS/MS. Chemical analysis denoted minor deviations of measured PBO concentrations in freshly prepared and old test solutions and between real and nominal concentrations in all labs. Other test conditions (water, food, D. magna clone, type of test vessel) varied across partners as allowed in the OECD test guidelines. Cumulative fecundity and intrinsic population growth rates (r) were used to estimate "No observed effect concentrations "NOEC using the solvent control as the control treatment. EC10 and EC-50 values were obtained regression analyses. Eleven of the twelve labs succeeded in meeting the OECD criteria of producing >60 offspring per female in control treatments during 21days in each of the two consecutive generations. Analysis of variance partitioning of cumulative fecundity indicated a relatively good performance of most labs with most of the variance accounted for by PBO (56.4%) and PBO by interlaboratory interactions (20.2%), with multigenerational effects within and across PBO concentrations explaining about 6% of the variance. EC50 values for reproduction and population growth rates were on average 16.6 and 20.8% lower among second generation individuals, respectively. In summary these results suggest that the proposed assay is reproducible but cumulative toxicity in the second generation cannot reliably be detected with this assay.

Inter-laboratory consistency and variability in the buccal micronucleus cytome assay depends on biomarker scored and laboratory experience: results from the HUMNxl international inter-laboratory scoring exercise.

The buccal micronucleus cytome (BMNcyt) assay in uncultured exfoliated epithelial cells from oral mucosa is widely applied in biomonitoring human exposures to genotoxic agents and is also proposed as a suitable test for prescreening and follow-up of precancerous oral lesions. The main limitation of the assay is the large variability observed in the baseline values of micronuclei (MNi) and other nuclear anomalies mainly related to different scoring criteria. The aim of this international collaborative study, involving laboratories with different level of experience, was to evaluate the inter- and intra-laboratory variations in the BMNcyt parameters, using recently implemented guidelines, in scoring cells from the same pooled samples obtained from healthy subjects (control group) and from cancer patients undergoing radiotherapy (treated group). The results indicate that all laboratories correctly discriminated samples from the two groups by a significant increase of micronucleus (MN) and nuclear bud (NBUD) frequencies and differentiated binucleated (BN) cells, associated with the exposure to ionizing radiation. The experience of the laboratories was shown to play an important role in the identification of the different cell types and nuclear anomalies. MN frequency in differentiated mononucleated (MONO) and BN cells showed the greatest consistency among the laboratories and low variability was also detected in the frequencies of MONO and BN cells. A larger variability was observed in classifying the different cell types, indicating the subjectivity in the interpretation of some of the scoring criteria while reproducibility of the results between scoring sessions was very good. An inter-laboratory calibration exercise is strongly recommended before starting studies with BMNcyt assay involving multiple research centers.

Zinc Isotopic Compositions of NIST SRM 683 and Whole‐Rock Reference Materials

In this study the homogeneity of the zinc isotopic composition in the NIST SRM 683 reference material was examined by measuring the Zn isotopic signature in microdrilled sample powders from two metal nuggets. Zinc was purified using AG MP‐1M resin and then measured by MC‐ICP‐MS. Instrumental mass bias was corrected using the “sample‐standard bracketing” method and empirical external normalisation with Cu doping. After evaluating the potential effects of varying acid mass fractions and different matrices, high‐precision Zn isotope data were obtained with an intermediate measurement precision better than ± 0.05‰ (δ66Zn, 2s) over a period of 5 months. The δ66ZnJMC‐Lyon mean values of eighty‐four and fourteen drilled powders from two nuggets were 0.11 ± 0.02‰ and 0.12 ± 0.02‰, respectively, indicating that NIST SRM 683 is a good isotopic reference material with homogeneous Zn isotopes. The Zn isotopic compositions of seventeen rock reference materials were also determined, and their δ66Zn values were in agreement with most previously published data within 2s. The δ66Zn values of most of the rock reference materials analysed were in the range 0.22–0.36‰, except for GSP‐2 (1.07 ± 0.06‰, n = 12), NOD‐A‐1 (0.96 ± 0.03‰, n = 6) and NOD‐P‐1 (0.78 ± 0.03‰, n = 6). These comprehensive data should serve as reference values for quality assurance and interlaboratory calibration exercises.

Uranium-series dating of fossil coral reefs: Extending the sea-level record beyond the last glacial cycle

Absolutely dated records of past sea-level change are extremely important for understanding the advance and retreat of the large ice sheets. When combined with other complementary climate archives and climate models, such records offer the potential to gain an improved understanding of Earth's natural climate cycles, providing a firmer basis for assessing the role of anthropogenic effects, such as greenhouse gas emissions, in modifying climate. The U-series dating of fossil coral reefs has been widely utilized to provide absolutely dated records of past sea-level change and numerous observations now exist for the past 130,000 years spanning the last glacial cycle. Despite this, controversies still exist regarding the exact timing and character of sea-level events within this time interval, and extending the sea-level history further back in time on the basis of robust and independent age constraints for older fossil reefs remains very elusive. This is primarily due to a progressive loss in the resolution of the U-series chronometer as one goes further back in time, coupled to a lack of well-preserved, dateable coral in older fossil reefs. To overcome these limitations, the primary challenges are three-fold. First, new analytical protocols are required to improve the resolution of the U-series chronometer. Enhanced analytical precision must be coupled to accuracy through continued refinement of the U-series decay constant determinations and via the implementation of rigorous inter-laboratory calibration exercises. Second, efforts should continue to be focussed on gaining an improved understanding of the mechanisms controlling open-system exchange of the U-series isotopes in fossil reef systems. This will allow the number of ‘reliable’ U-series observations to be extended. Third, alternative dateable archives of past sea-level change must continue to be emphasized to further complement the coral reef database. These limitations are discussed in the context of current developments that further advance the application of U-series chronology to older fossil reef systems formed prior to the last glacial cycle.

Determining the absolute abundance of dinoflagellate cysts in recent marine sediments: The Lycopodium marker-grain method put to the test

Absolute abundances (concentrations) of dinoflagellate cysts are often determined through the addition of Lycopodium clavatum marker-grains as a spike to a sample before palynological processing. An inter-laboratory calibration exercise was set up in order to test the comparability of results obtained in different laboratories, each using its own preparation method. Each of the 23 laboratories received the same amount of homogenized splits of four Quaternary sediment samples. The samples originate from different localities and consisted of a variety of lithologies. Dinoflagellate cysts were extracted and counted, and relative and absolute abundances were calculated. The relative abundances proved to be fairly reproducible, notwithstanding a need for taxonomic calibration. By contrast, excessive loss of Lycopodium spores during sample preparation resulted in non-reproducibility of absolute abundances. Use of oxidation, KOH, warm acids, acetolysis, mesh sizes larger than 15 µm and long ultrasonication (> 1 min) must be avoided to determine reproducible absolute abundances. The results of this work therefore indicate that the dinoflagellate cyst worker should make a choice between using the proposed standard method which circumvents critical steps, adding Lycopodium tablets at the end of the preparation and using an alternative method.

Improved fluorimetric determination of dissolved aluminium by micelle-enhanced lumogallion complex in natural waters.

A modification of the aluminium-lumogallion fluorescence measurement in the presence of the non-ionic surfactant Triton X-100 is presented. The detection limit for dissolved Al is 0.7 nM, with a relative standard deviation of 3.6% at an Al level of 5.0 nM. Compared with previously reported methods in the literature, the method described here is free from matrix effects and can be used for the determination of aluminium in fresh, estuarine and saline waters. The interferences from iron and fluoride were minimized by the addition of o-phenanthroline and Be2+, respectively. The analysis of NIST SRM 1643C and PRC standard 2430101 by the proposed method provides results consistent with the certified values. A successful inter-laboratory calibration exercise also demonstrates the merit of the proposed method for the determination of Al in environmental and marine sciences.

The ISO headspace CO 2 biodegradation test

Two published methods for evaluating the aerobic biodegradability of organic compounds by measuring inorganic carbon (CO 2) production in sealed vessels, under a headspace of air were combined into one protocol. This was ring tested in 1995 by the International Organization for Standardization (ISO) using aniline and 1-octanol as the test substances. This paper describes the ISO method and discusses the results of the inter-laboratory calibration exercise in terms of the method's precision and performance.

Design and Preparation of Samples for the International Collaborative Study

Sample materials issued to participants in the interlaboratory calibration exercise are defined and in context of their intended interpretational significance. Preparation of the benzene and calcium carbonate standards as issued for stage 1 is described in detail; likewise, the source and pretreatment/extraction of the environmental samples dispatched for stages 2 and 3.

Inter-laboratory calibration for the quality control of pesticide residue analyses (1984-85).

Five inter-laboratory calibration exercises (ICEs) carried out in South Africa during 1984 and 1985 are described. Analyses were carried out on solutions of pesticides and on residues in butter, maize meal, soil, eggs and grape juice. The results seem to indicate an improvement in the quality of pesticide residue analysis since the inception of the ICE programme.

Quality assurance in pesticide formulation analysis.

Five inter-laboratory calibration exercises were carried out with pesticide formulations in South Africa during 1984 and 1985. These exercises included the determination of the active ingredient and other components, and also physical testing of the formulated product. The use of gas chromatography to determine the active ingredients seemed to present few problems but an HPLC exercise gave poor results. The results of the physical testing of formulations indicated much variability between results, which must be rectified.

The reproducibility in the determination of heavy metals in marine plant material — an interlaboratory calibration

Results from an interlaboratory calibration exercise on the reproducibility in the determination of cadmium, chromium, copper, iron, manganese, nickel, lead, and zinc in marine plant material are presented. The fourteen participating laboratories each analysed the heavy metal content in two samples of dried eelgrass material (spiked and unspiked), a predigested sample, and a mixed standard solution. Significant variations in the reported heavy metal concentrations were observed. The variability between laboratories was greatest for cadmium, chromium, nickel, and lead, whereas the variability for iron, manganese, and zinc was less. The reproducibility in reported heavy metal concentrations was generally best in the mixed standard solution and poorest in the dried eelgrass samples. Statistical analyses showed that some laboratories generally reported values closer to the overall means than did others. The sources of variation are discussed, and recommendations to improve the quality of heavy metal analyses are given.

Inter-laboratory calibration for pesticide analysis in South Africa

The organising and running of four inter-laboratory calibration exercises in South Africa in 1981 are described. Analyses of a solution containing pesticides, margarine and fruit pulp fortified with pesticides and a potato sample with incurred residues were carried out. The results indicate that most laboratories produced acceptable results. This type of exercise should be continued.