Presentation on theme: "How Much Arsenic Do We Eat? Department of Chemistry"— Presentation transcript:
1 How Much Arsenic Do We Eat? Department of Chemistry Analytical chemists make light work in tracking potentially harmful chemicalsJulian TysonDepartment of ChemistryUMass AmherstStart by getting some measurements underway. Rice, presssure- treated wood, water, and the apple juice.
2 Interaction of light with materials. Analytical chemists provide information about the chemical composition of materials. So that a decision can be taken.How do analytical chemists make light work in tracking potentially harmful chemicals?I am going to show you some of the ways that light interacts with materials. Explain how we can use this to get information about the chemical composition of materials. Start with a familiar experiment.Interaction of light with materials.
3 Light is a wave and is a form of energy Light is a wave and is a form of energy. The energy of light is inversely related to its wavelength.Short wavelength: high energy.Long wavelength: low energy
4 Summary of where we are now. Color of objects is due to the absorption of light.Absorption is due to the molecules.The wavelengths of the light absorbed tell us something about which chemicals are present.Amount of light absorbed depends on the number of molecules in the light beam, soThe extent of the absorption tells us something about how much of a chemical is present.More demonstrations. We can use CHEMICAL REACTIONS. If the product of the reaction is colored (or has a different color from the reactants) then we can measure the amount of light absorbed following reaction with an excess of reagent.
5 Analytical chemists use the interaction of light with with molecules that contain arsenic to measure the arsenic in relevant materials.
6 So how does arsenic get into relevant materials? Arsenic occurs in nature. It is about the 40th most abundant element on the planet. Geological processes have spread it around. We’ve extracted it from ores, made useful compounds and spread them around.Open ocean water: about ppbRiver and surface water:about ppb
7 The arsenic in the environment story Orpiment As2S3Realgar As4S4Arsenic trioxide As2O3Arsenic As
8 Ground water: a major problem around the world Ground water: a major problem around the world. Especially in SE Asia (Bangladesh and West Bengal, India)Concentrations: 0.1 – 1000 ppb.US EPA limit is 10 ppb
9 Concentrations in soil are about 2 mg kg-1 Concentrations in soil are about 2 mg kg-1. But there are considerable variations and there’s a legacy of previous agricultural practice to deal with.I need to take a few minutes to talk about the units of amount and concentration that are relevant.
10 Amounts. Weight:1 kilogram (kg) = 2.2 lb = 1,000 grams (g)1 milligram (mg) = one-thousandth of a gram1 microgram (µg) = one-millionth of a gram.A grain of salt weighs 2 mg(the official grain is 65 mg)Amounts. Volume:liter (L) = 0.26 gallon (US) = 1,000 milliliters (mL)1 milliliter (mL) = one-thousandth of a liter1 microliter (µL) = one-millionth of a literA drop (of water) is about 50 µLA bathtub contains about 230 L
11 Concentrations in solids: mass per mass 1 part per million (ppm) is 1 milligram in 1 kilogram i.e. 1 mg/kgor 1 microgram in 1 gram i.e. 1 µg/gScientist sometimes write this as 1 µg g-1A part per billion (ppb) is 1 µg kg-1Concentrations in liquids: mass per volume1 part per million (ppm) is 1 milligram in 1 liter i.e. 1 mg/Lor 1 microgram in 1 mL i.e. 1 µg/mLScientist sometimes write this as 1 µg mL-1A part per billion (ppb) is 1 µg L-1Concentration is the relative amount1000 ppb = 1 ppm
12 How to make a 10 pbb solution One grain weighs 65 mg(2.5 mm cube of As2O3)76% by weight is As49 mg21 bathtubs contain21 x 233 L = 4,900 L1 grain in 21 bathtubs = 10 ppbThe US EPA limit for arsenic in drinking water
13 Arsenic speciationThere are a lot of different arsenic compounds in the environment.InorganicArsenic bonded to oxygen and/or sulfur or hydrogen.As2O5 H3AsO4 arsenateAs2O3 H3AsO3 arseniteAsH arsineOrganicArsenic bonded to carbon and/or oxygen or hydrogenMethylated arsenateCH3AsO(OH) MMA(CH3)2As(O)OH DMAArsenobetaine, arsenocholine
14 Some formulae for the chemists in the audience. arsenatemonomethylarsonatearseniteThe monomethyl compound is sold as a herbicide and fungicie under the name of MSMA monosodium methylarsonate. The other oxgen is protonated, so the official IUPAC name is sodium hydrogen methylarsonatecacodylatedimethylarsinatetrimethylarsine oxide
15 More formulae for the chemists in the audience. trimethylarsine oxidetetramethylarsonium
16 Yet more formulae for the chemists in the audience. TETRAarsenobetainePictures of fish.You have to be a big careful with the names of arsenic compounds as there is a certain class that apparently the Synthonix Company does not sell.Seafood arsenicarsenocholine
17 Not all arsenic compounds are very toxic OK - all chemicals are toxic: it all depends on the dose and how you interact with them.Some arsenic compounds are “non-toxic.”arsenobetaine and arsenocholine and arsenosugarsseafood arsenicSome arsenic compounds are toxicAcute lethal dose of As2O3 is about 100 mg for a 70-kg adult.About 2 grains or a 3 mm cube.Some arsenic compounds are sort of non-toxicMonomethyl and dimethyl arsenatesThe adverse health effect of concern is cancer.
18 How does arsenic get into our food How does arsenic get into our food? Plants take up arsenic compounds from the soil. Legacy of previous applications.
19 How arsenic gets into crops Irrigation with contaminated ground water.
20 Ask the analytical chemists. They tell us. How do we know whether food and drink contains potentially harmful forms of arsenic?Ask the analytical chemists. They tell us.Seafood contains non-toxic formsDrinking water contains toxic, inorganic formsFood contains toxic (inorganic) and sort-of toxic forms (mono- and di- methylated).Approach: Measure total arsenic and assume it is all toxic.If less than guideline value: no problemIf more than guideline value: more analysis neededAsking a scientist usually means finding what he or she has reported about the results of his or her research. This means looking in the science journals for articles that are relevant.
21 3.0 µg per kg body weight per day How much arsenic is considered safe?How much inorganic arsenic is considered safe?Food: No US guideline value.Drinking water: US EPA 10 µg L-1 (ppb)Joint FAO/WHO expert committee on food additives, seventy-second meeting, Rome, 16–25 February 2010, summary and conclusions Issued 16th March 2010The limit for dietary inorganic arsenic exposure is:Food and Agriculture Organization of the United Nations and the World Health Organization. OK so what do people weigh?3.0 µg per kg body weight per day
22 Tolerable daily intake µg Acute lethal dose (adult) 100 mg How much inorganic arsenic is considered safe?Dietary: 3.0 µg per kg body weight per day.Developmental stageWeight lbs1 lb = 0.45 kgTolerable daily intake µgNewborn791-year-old22305-year-old4257teenager140 (m) 117 (f)191 (m) 160 (f)young adult155 (m) 127 (f)211 (m) 173 (f)Adult (US average)191 (m) 164 (f)260 (m) 224 (f)football player300409overweightyour call> 400Acute lethal dose (adult) 100 mg
24 A market basket survey of inorganic food in rice Food and Chemical Toxicology 37 (1999)Examined 40 commodities expected to deliver 90% of total dietary inorganic arsenic. Took 4 samples of each. Measured total arsenic and inorganic arsenic.
25 Food Total arsenic µg kg-1 wet weight Inorganic arsenic saltwater finfish2,4000.5shrimp1,9002tuna5121rice30374chicken86grape juice589beef520.4peanut butter445watermelon40flour3911spinach6apple juice83Moisture content of rice is about 10%. Of course the exposure depends on how much of each food stuff we eat. Ask a scientist.
26 Environmental Health Perspectives, 2010, 118, 345-350 Probabilistic modeling of dietary arsenic exposure and dose and evaluation with NHANES DataScientists at US EPA, National Taiwan University, and the Environmental and Occupational Health Sciences InstituteInorganic arsenic.121124NHANES is National Health and Nutrition Examination Survey.1817135
27 Environmental Health Perspectives, 2010, 118, 345-350 Results: Mean total exposure from food is 0.38 µg per kg body weight per day. 14-times higher than the mean exposure from drinking water. Exposure from food is 0.05 µg per kg body weight per day i.e µg per day.Approximately 10% of exposure from food is the toxic inorganic form of arsenic.We can do the calculation and deduce that the average American weighs 88lbs (click). So averages are not telling us anything very useful. We need to look at the spread or the distribution.The average Americanweighs 40 kg i.e. 88 lbs.
28 Age Number Average 5th percentile 99th percentile Calculated exposure from food.Total arsenic: µg per kg body weight per dayAgeNumberAverage5th percentile99thpercentile0 - 17570.620.052.081 - 21,0680.545.063 -59630.035.66-122,1900.370.024.2813 -193,5760.250.013.584,2210.334.12>503,8040.324.91All16,9310.364.45Remember that the FAO/WHO guideline is 3. This is TOTAL arsenic. Most are above 3.
29 Age Number Average 5th percentile 99th percentile Calculated exposure from food.Inorganic arsenic: µg per kg body weight per dayAgeNumberAverage5th percentile99thpercentile0 - 17570.230.010.81 - 21,0680.10.593 -59630.080.46-122,1900.040.2513 -193,5760.030.214,2210.28>503,8040.22All16, 9310.050.41The inorganic numbers are about a factor of 10 less than the total. Remember that food is not the only source of inorganic arsenic. We are exposed through drinking water as well. Should be concerned about the reliability of the measurements that distinguish inorganic arsenic from other forms. Let’s ask the scientists how well they can do that.
30 The Schoof report: A market basket survey of inorganic food in rice Total arsenicµg kg-1 wet weightInorganic arsenicrice30374Total arsenicInorganicMMADMAI + MMA + DMA% missing33555ND842186261123444628132022863819697299198There’s a problem with the Schoof analysis of the rice.
31 The average total content was 210 µg kg-1. What do other researchers find about arsenic in rice?Food Additives and Contaminants: Part B, 2009, 2,Survey of total arsenic and arsenic speciation in US-produced rice as a reference point for evaluating change and future trends.Heitkemper and colleagues at USFDA CincinnatiThe average total content was 210 µg kg-1.Regardless of total content, inorganic arsenic rarely exceeded 150 µg kg-1.Arsenic content in US rice has been relatively constant over the past 30 years.
32 Date Location Total Inorganic % missing* All values in µg kg-1 based on dry weight.DateLocationTotalInorganic% missing*LA167105-9AR18479-11TX445#111CA6261-33AVE US20290-1326498The difference between Total and inorganic was accounted for by DMA and MMA. The vast majority of the organic arsenic was MMA*The minus sign means that the sum of I + MMA + DMA > total#One sample had over 1000 µg kg-1 total: inorganic 150 µg kg-1
33 Heitkemper and colleagues at US FDA Cincinnati Conclusions“In comparison with inorganic arsenic, much less is known regarding the toxicity and biotransformation pathways associated with dietary intake of DMA.Although generally considered to be less toxic than inorganic arsenic, more information about the long-term exposure effects of DMA may be necessary to evaluate fully the risk of rice consumption, given the high DMA content that has been reported in rice.”
34 What do other researchers find about arsenic in rice? Meharg and colleagues at the University of Aberdeen
35 Location Average Total Max total Average inorganic Max inorganic Arsenic in rice around the world. All values in µg kg-1LocationAverage TotalMax totalAverage inorganicMax inorganicBangladesh13033080210China140460160380Egypt50580No dataFrance280560India7018030Italy150110Japan190420Spain200820Thailand390USA250660100No information on the reliability of the distinction between inorganic and methylated forms.
36 Meharg and colleagues at the University of Aberdeen Conclusions “The modeling outlined here indicates that eating rice at typical SE Asia consumption rates, or at higher percentile consumption rates in developed countries, constitutes a significant excess cancer risk to those populations, well above the targets set by US EPA and WHO for carcinogenic sources.”“As cancers caused by chronic exposure to arsenic sources have a latency of approx. 20 years, the data presented here suggest that long-term epidemiological studies need to be undertaken to characterize this risk.”We could go on asking scientists like this and you would rapidly get bored. So just one more before we go back to the experiments.
37 Researchers call for monitoring of arsenic levels in rice By Elizabeth Weise, USA TODAY Dec 5, 2011Proceedings of the National Academy of Sciences of the USA Dec 5th 2011Rice consumption contributes to arsenic exposure in US womenDiane Gilbert-Diamond and coworkers at Dartmouth College“Emerging data indicate that rice consumption may lead to potentially harmful arsenic exposure.”“Although inorganic arsenic is thought to be more harmful that DMA, further epidemiological studies are needed to better understand the health risks of DMA It is imperative that the health impact of arsenic exposure through rice consumption be characterized.”Epidemiology: The branch of medicine that deals with the incidence, distribution, and control of diseases. Toxicology The branch of science concerned with the nature, effects, and detection of poisons.
38 How Much Arsenic Do We Eat? The question really should be: How much inorganic arsenic and methylated arsenic do we eat?Answer: depends on what foods we eat. Rice has a much higher concentration than any other food.What sort of rice, where from and how much.White rice contains less arsenic than brown rice.Where grown. USA, France, and Spain (max total)China, Bangladesh and Italy (max inorganic).Bioavailable? Assume 100%.
40 88 samples purchased in Aug and Sept 2011 in CT, NJ, and NY. Date of this article is
41 Need to drink 1.2 – 2.4 L i.e. 2.5 – 5 pints per day. There’s no federal limit for arsenic in juice.25% of samples exceeded 5 ppb and 10% exceeded 10 ppb.Recommended dietary limit is 3 µg per kg body weight per day.µg for young children.If you are quick at the mental arithmetic, you’ll notice that there’s up to 23% of the arsenic missing.Now we need to look at the results of the tests we started at the beginning of the lecture.Need to drink 1.2 – 2.4 Li.e – 5 pints per day.
42 Take digital picture with digital camera. If you are helping with the project. Send the picture to me or you can try the image analysis yourself.