Arsenic in Food. Presented by Michelle Briscoe President & Technical Director Brooks Rand Labs

Transcription

1 Arsenic in Food Presented by Michelle Briscoe President & Technical Director Brooks Rand Labs Presented November 8, 2013 Costco International QA & Food Safety Summit Issaquah, Washington

2 Small analytical chemistry firm located in Seattle Exclusively focused on metals in food & the environment ISO Accredited

3 Primary Metals of Concern The Big 4 Total Arsenic (As) Total Cadmium (Cd) Total Lead (Pb) Total Mercury (Hg) < 10 ppb detection available using ICP-MS method Metals Speciation Inorganic Arsenic (ias) Methylmercury (MeHg) Other USP Metals Selenium Speciation So Much More!

4 Metals Speciation What is Metals Speciation? Analytical quantification of the different forms that a metal is present in Why is Speciation Important? Different forms of metal can have different characteristics: Toxicity Bioavailability Mobility Treatability

5 Arsenic Speciation A Hot Topic Recently (and not so recently ) Fish with 500 ppb As = YUM! Rice with 500 ppb As = YIKES! The forms of arsenic found in fish are very different from the forms of As found in rice: Organic As - predominant form is seaweed, fin fish, kelp, shellfish Inorganic As - predominant form in rice, produce, groundwater

6 Inorganic Arsenic Forms Toxic carcinogens Arsenite, As(III) Arsenate, As(V) AsO 3 3- AsO 4 3- Inorganic As is classified as a known human carcinogen by the Agency for Toxic Substances and Diseases Registry (US ATSDR), the Environmental Protection Agency (US EPA), and the World Health Organization s International Agency for Research on Cancer (IARC).

7 Methylated Arsenic Forms Potentially toxic Monomethylarsonic acid, MMAs Dimethylarsinic acid, DMAs MMAs (III) may be more toxic than As(III), while MMAs (V) is less toxic Also called cacodylic acid, DMAs is formed in the liver after ingesting inorganic As

8 How are Methyl Arsenic Compounds Formed? Biological methylation reactions require alternating reduction and oxidation steps

9 Other Organic Arsenic Forms Relatively non-toxic AsB Roxarsone AsC Arsenobetaine very common As compound and is the main source of arsenic found in fish Roxarsone is a controversial arsenic compound used as a nutritional supplement for chickens and swine Arsenocholine is found in many marine organisms And MANY others

10 Toxicity of Different As Species Toxicity of individual arsenic species is dependant on: The general form (e.g., inorganic vs. organic) The oxidation state of the arsenical The organism s detoxification mechanisms and bioaccumulation factors MMAs (III) > As(III) > As(V) >> MMAs (V) = DMAs (V) > DMAs(III) >> AsB = AsC = arsenosugars As(III) is about 300 times more toxic than AsB

11 Analytical Methods For the speciation of arsenic

12 Many Methods Available Hydride Generation w/cryotrapping & AAS Hydride Generation & AFS Liquid Chromatography & ICP-MS Anion exchange chromatography Reverse phase ion pairing chromatography Size exclusion chromatography

13 Many Methods Available Hydride Generation w/cryotrapping & AAS Hydride Generation & AFS Liquid Chromatography & ICP-MS Anion exchange chromatography Reverse phase ion pairing chromatography Size exclusion chromatography

14 HG - CT- GC - AAS EPA Method 1632 Pros Determines Inorganic As with a quick, easy, and inexpensive method Decades of proven reliability Codified in EPA Method (for water and fish) Good for measuring ias in samples high in AsB and AsC Very sensitive: < 0.1 ppb for water samples < 3 ppb for solid samples Cons Operationally-defined As(V) determined by calculation [Inorganic As As(III)] Very labor intensive Cannot measure AsB, AsC, arsenosugars While common in environmental sectors, less common in food testing labs

15 IC - ICP - MS Pros Measures many different forms directly and simultaneously with anion exchange Reasonably sensitive: < 0.2 ppb for water samples < 20 ppb for solid samples Lots of options for columns, mobile phase, etc. outlined in the literature Usually, just one extractant works well for all species Cons Prone to interference from chlorides use interference reduction technology such as DRC or collision cell with ICP-MS High AsB can swamp DMAs and As(III) results Some organic compounds are better determined by cation exchange, requiring a 2 nd method Expensive equipment Relatively new to a lot of labs still some issues with species identification and co-elution

16 2013 Brooks Rand Labs Interlaboratory Comparison Study for Arsenic Speciation in Food and Juice

17 Goals of the Study To provide a reliable means for laboratories to evaluate their competency at quantification of arsenic species in food To provide a metric for assessing the intercomparability of arsenic speciation data generated by different laboratories

18 Key Features of the Study broad invitation to participate no participation fee large group of participating laboratories from around the world anonymous data submission inclusion of analytical method reporting

19 SELECTED STUDY MATERIALS Criteria for selection: Foods that were hot topics for arsenic Must have > 10 ppb in total arsenic Minimal processing required Cheap THANKS TO US FDA, UC DAVIS, AND AGILENT TECHNOLOGIES FOR THEIR ASSISTANCE!

20 Study Materials 1) White Rice 2) Brown Rice 3) Kelp 4) Apple Juice

21 2013 Intercomp Study Schedule January February February 7 th March April 1 st June 7 th June 14 th August 26 th August 27 th Sample procurement Sample screening for total arsenic Registration opens More sample procurement & screening Samples shipped out to labs Deadline for results submission Anonymized data delivered to BRL Final report for study issued Study results presented at AOAC International Annual Meeting in Chicago, Illinois

22 International Participation Region Number of Participants North America 25 64% Europe 8 21% Other 6 15%

23 Analytical Parameters for Study Total Arsenic (As) in the sample Total As in the extract (if applicable) Inorganic As As(III) - arsenite As(V) - arsenate MMAs monomethylarsonic acid DMAs dimethylarsinic acid Other arsenic species, such as arsenobetaine (AsB) or unknown arsenic species

24 Data Analysis Each laboratory was asked to report the following for each sample and analyte: Analytical result Detection limit Date analyzed Data qualifier (limited to u and nm only) Detailed methodology information

25 Results M Values (μg/kg) White Rice Flour Brown Rice Flour Total As in Sample Total As in Extract As(III) As(V) Inorg As MMAs DMAs AsB (6.49) (2.86) 8.49 ND (2.75) 7.71 ND Kelp Powder (3790) (1530) (1467) 3837 Apple Juice (0.60) (0.35) ND

26 As Speciation (as function of total As in extract)

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28 Statistical Analysis Z-Value Calculation Based on USGS procedure for round robins Z = (X-M) /F and F = Q/1.349 Z = absolute Z-value assigned to each result for assigning a rating X = reported value M = median value reported by all laboratories (excluding NDs) F = F-pseudosigma (approximates the Std Dev) Q = Interquartile range

29 Description of Ratings Rating Absolute Z-value 4 (Excellent) (Good) (Marginal) (Poor) (Unacceptable) Greater than 2.00 Scores were not assigned if: - the overall number of data points was less than seven - the variance (F-pseudosigma value) was greater than the median value (M)

30 Overall Mean Scores All Matrices Number of Labs Mean Score Parameter Mean Score n Total As in Sample Total As in Extract As(III) As(V) Inorganic As DMAs All Parameters

31 Mean Scores by Matrix 16 White Rice 16 Brown Rice Number of Labs Number of Labs nm Mean Score nm Mean Score

32 Mean Scores by Matrix Kelp Powder 16 Kelp Powder 14 Apple Juice Number of Labs Number of Labs nm nm Mean Score Mean Score

33 Lessons Learned & Future Work (for next year?) Inconsistent reporting of inorganic arsenic Potential misidentification of some forms of arsenic Unable to ship materials to Mexico More expensive than anticipated Study report is available upon request, and is currently being prepared for submission to a peerreviewed journal for publication Next Year?

34 THANK YOU! ANY QUESTIONS?