A method that uses liquid chromatography with tandem mass spectrometry (LC/MS/MS) has been developed for the highly sensitive and specific determination of amnesic shellfish poisoning toxins, diarrhetic shellfish poisoning toxins, and other lipophilic algal toxins and metabolites in shellfish. The method was subjected to a full single-laboratory validation and a limited interlaboratory study. Tissue homogenates are blended with methanol-water (9 + 1), and the centrifuged extract is cleaned up with a hexane wash. LC/MS/MS (triple quadrupole) is used for quantitative analysis with reversed-phase gradient elution (acidic buffer), electrospray ionization (positive and negative ion switching), and multiple-reaction monitoring. Ester forms of dinophysis toxins are detected as the parent toxins after hydrolysis of the methanolic extract. The method is quantitative for 6 key toxins when reference standards are available: azaspiracid-1 (AZA1), domoic acid (DA), gymnodimine (GYM), okadaic acid (OA), pectenotoxin-2 (PTX2), and yessotoxin (YTX). Relative response factors are used to estimate the concentrations of other toxins: azaspiracid-2 and -3 (AZA2 and AZA3), dinophysis toxin-1 and -2 (DTX1 and DTX2), other pectenotoxins (PTX1, PTX6, and PTX11), pectenotoxin secoacid metabolites (PTX2-SA and PTX11-SA) and their 7-epimers, spirolides, and homoYTX and YTX metabolites (45-OHYTX and carboxyYTX). Validation data have been gathered for Greenshell mussel, Pacific oyster, cockle, and scallop roe via fortification and natural contamination. For the 6 key toxins at fortification levels of 0.05–0.20 mg/kg, recoveries were 71–99% and single laboratory reproducibilities, relative standard deviations (RSDs), were 10–24%. Limits of detection were <0.02 mg/kg. Extractability data were also obtained for several toxins by using successive extractions of naturally contaminated mussel samples. A preliminary interlaboratory study was conducted with a set of toxin standards and 4 mussel extracts. The data sets from 8 laboratories for the 6 key toxins plus DTX1 and DTX2 gave within-laboratories repeatability (RSDr) of 8–12%, except for PTX-2. Between-laboratories reproducibility (RSDR) values were compared with the Horwitz criterion and ranged from good to adequate for 7 key toxins (HorRat values of 0.8–2.0).
agencies for countries with a signiücant tropical area should encourage üeld validation and/or modelling rather than require additional laboratory studies as a means of obtaining the most useful and regionally speciüc information on pesticide fate in tropical soils.(2) Further comparisons of pesticide fate in tropical and temperate soils. Additional comparisons of pesticide fate in tropical and temperate soils should be made with the same experimental design. Execution of laboratory and üeld protocols across tropical and temperate soils or areas, inasmuch as they contribute to assembly and validation of pesticide fate models with broad, international applicability, would be especially valuable.(3) Application of modelling to pesticide fate under tropical conditions. Further attempts should be made to validate environmental fate models for application to simulation of pesticide dissipation and mobility under tropical conditions. (4) Publication of data re fate of pesticides in tropical soils. Results of investigations on pesticide fate in tropical soils should be published in international, peer-reviewed journals whenever possible, to increase accessibility of the information and insight obtained. Published reports should contain sufficient experimental information and data analysis to answer questions related to efficacy and environmental safety, so as to allow comparison with results from temperate areas. SUMMARYPrediction of pesticide residue intake in human diets is vital for approving the use of pesticides and for gaining official acceptance of pesticide residue levels which occur in food commodities in international trade. Estimates for pesticide residue levels likely to be present in food as consumed are derived from supervised pesticide residue trials, residue monitoring, pesticide metabolism and food processing studies. The results of properly conducted total diet studies should generally displace other estimates, but they do not cover all pesticides and, in particular, are not available for a pesticide at its initial registration. Information was compiled on the range of residues Corres pondence to : DJ Hamilton, occurring in a set of supervised residue trials with identical application rate, number of applications and pre-harvest interval, but at diþerent sites with various crop varieties, operators, equipment and cultural practices. Where there were eight or more trials in a set (one data point per trial) the median residue was commonly 20-40% of the maximum and 80-100% of the mean. The median was generally a good measure of the modal or most commonly occurring value. The median residue in the edible portion of the commodity in the supervised trials (supervised trials median residue, STMR) was chosen as the starting point for chronic dietary intake estimation. The residue deünition for dietary intake purposes should include metabolites and degradates of toxicological concern. Dietary intake for acute eþects is best related to residue levels in a single serving of a food, or at least the average residue...
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