Differentiation Between Nutritional and Carcinogenic Selenium via Speciation Analyses

Transcription

1 Presented at the AOAC Conference, September 29, 2015 Differentiation Between Nutritional and Carcinogenic Selenium via Speciation Analyses Russell Gerads Business Development Director Brooks Applied Labs

2 Presentation Outline: I thought selenium was a nutrient Selenium sources Applied Analytical Methods Analytical Findings Implications for Humans, Cattle, Fish, and the Ecosystem

3 I Thought Selenium was a Nutrient Selenium is an essential trace element Deficiency is widespread and causes increased cancer rates Efforts to enrich nutrition in Se are underway in many areas Reduces certain types of cancer (antioxidant in the form of glutathione peroxidase) Reduces As toxicity (Se-As complexes) Reduces Hg bioaccumulation (Se-Hg complexes)

4 I Thought Selenium was a Nutrient Se biomagnifies (review in a few minutes) Effects observed: Teratogenicity Mutagen Decreases reproductive efficiency Cirrhosis of the liver Most organic-se compounds are readily absorbed (increased uptake), but inorganic Se species dominate in the environment; somewhere along the process, conversion of inorganic Se into organic Se species must occur (rate limiting step) Selenate mobilized through sulfate chemical pathways for plants (greater efficiency than selenite)

5 I Thought Selenium was a Nutrient

6 I Thought Selenium was a Nutrient

7 I Thought Selenium was a Nutrient

8 Biochemical Implications Sulfur and oxygen analogues Volatile methylated compounds (CH 3 -Se-CH 3, CH 3 -Se-Se-CH 3, CH 3 -SeO 2 -CH 3 ) Se-amino acids and Se proteins Selenoamino acids (sulfur analogues) Selenomethionine Selenocysteine Other

9 Biochemical Implications

10 Which Selenium is Nutritional?

11 Which Selenium is Nutritional? Source: Rigby, M., Gerads, R., Lemly, D. Environmental Science Process & Impacts 2014

12 Selenium Sources Electronics (diodes, photoelements, rectifiers, LEDs) Vulcanizing agent for rubber Medicine / nutritional supplement Vegetation, groundwater, feed, food additives (human too!) Coal combustion (fly ash) Flue gas desulphurization (FGD) Oil refining Manufacturing gas plants Coal and phosphorus mining Runoff from agricultural irrigation in arid regions Se is produced from anodic sludge in copper refining and from lead chamber sludge in sulfuric acid production

13 Selenium Sources Selenium production from copper mines and anode mud from electrolytic Cu refineries: Cu 2 Se + Na 2 CO 3 + 2O 2 2CuO + Na 2 SeO 3 + CO 2 Acidified with sulfuric acid forming H 2 SeO 3 H 2 SeO 3 + 2SO 2 + H 2 O Se (s) + 2H 2 SO 4

14 Applied Analytical Methods Size exclusion inductively coupled plasma dynamic reaction cell mass spectrometry (SEC-ICP-DRC-MS) Selenoproteins and selenoamino acids Ion chromatography inductively coupled plasma dynamic reaction cell mass spectrometry (IC-ICP-DRC-MS) Se(IV), Se(VI), SeCN, MeSe(IV) Reverse phase chromatography inductively coupled plasma dynamic reaction cell mass spectrometry (RP-ICP-DRC-MS) Seleno-amino acids and other small molecular metabolites Extraction for selenoamino acids must be specific to intent: selenoamino acids versus selenoproteins Different selenoamino acids and proteins applied to inorganic selenium extraction method to confirm molecular degradation did not transpire

15 Applied Analytical Methods Many published methods use or reference EXAFS/XANES Problem: Utility of method limited to adjacent atoms Many gross assumptions made regarding molecular forms using x-ray spectrometry For more information please read: Rigby, M., Lemly, D., Gerads, R. Fish toxicity testing with selenomethionine spiked feed what's the real question being asked? Environmental Sci.: Processes & Impact. 2014, 16, 511.

16 Selenium Speciation Analysis by SEC-ICP-MS A B Column Oven LC Pump Autosampler Column ICP-MS Computer Waste

17 Selenium Speciation Analysis by SEC-ICP-MS Size exclusion inductively coupled plasma mass spectrometry (SEC-ICP- MS) Selenoproteins and selenoamino acids Small molecules Large molecules Flow Molecular identification by retention times for known standards (macro molecules require monitoring for other elements)

18 Selenium Speciation Analysis by SEC-ICP-MS SeP Se-amino Se(IV) SeCN

19 Selenium Speciation Analysis by IC-ICP-MS Ion chromatography inductively coupled plasma dynamic reaction cell mass spectrometry (IC-ICP-DRC-MS) Se(IV), Se(VI), SeCN, MeSe(IV) Large molecules Small molecules separated by ionic interactions Flow Molecular identification by retention times for known standards

20 Selenium Speciation Analysis by IC-ICP-MS

21 Selenium Speciation Analysis by RP-ICP-MS Reverse phase chromatography inductively coupled plasma mass spectrometry (RP-ICP-DRC-MS) Se(IV), Se(VI), selenomethionine, selenocysteine, methylselenocystein, other seleno-amino acids Large molecules Small molecules separated by carbon and ionic interactions Flow Molecular identification by retention times for known standards

22 Selenium Speciation Analysis by IC-ICP-MS Full Time Range EIC(78) : 017SMPL_ ICPMS7-IC-SeMet-2_ ICPMS7-IC-SeMet Crunch.D x10 3 Enzymatically extracted yeast sample analyzed by RP-ICP-MS 2 1 Compound Name=SetMetExp. RT= Det. RT= Area=595259Height=31104 Compound Name=Se4Exp. RT= Det. RT= Area=11892Height=1604 >85% SeMe nd Name=O-setmetExp. RT= Det. RT= Area=6407Height= Count RT(min)

23 Selenium Speciation Analysis by IC-ICP-MS Full Time Range EIC(78) : 085SMPL_ SeMet.D x10 2 Enzymatically extracted yeast sample analyzed by RP-ICP-MS 4 2 Compound Name=Se4Exp. RT=4.328Det. RT=4.047Area=229947Height=31053 >90% Se(IV) Compound Name=SeMetExp. RT=3.347Det. RT=3.347Area=49Height=13 0 Count RT(min)

24 Implications for Humans, Cattle, Fish, and the Ecosystem Toxicological risk dictated by organism Not all food additives are the same Selenized yeast Risk concerns: Human < Cattle < Fish < Birds Selenium supplementation for cattle routine Application of incorrect molecular form of selenium may have negative effects on yield Application of cattle waste to agriculture can have negative side effects depending on cattle feed Increased attention from FWS, USDA, and EPA for agricultural runoff resulting in higher costs for industry over time

25 Acknowledgments Thanks! to: Brooks Applied Labs staff Dr. Hakan Gurleyuk