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How Much Arsenic Do We Eat? Department of Chemistry

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1 How Much Arsenic Do We Eat? Department of Chemistry
Analytical chemists make light work in tracking potentially harmful chemicals Julian Tyson Department of Chemistry UMass Amherst Start 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, so The 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 ppb River and surface water: about ppb

7 The arsenic in the environment story
Orpiment As2S3 Realgar As4S4 Arsenic trioxide As2O3 Arsenic 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 gram 1 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 liter 1 microliter (µL) = one-millionth of a liter A drop (of water) is about 50 µL A 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/kg or 1 microgram in 1 gram i.e. 1 µg/g Scientist sometimes write this as 1 µg g-1 A part per billion (ppb) is 1 µg kg-1 Concentrations in liquids: mass per volume 1 part per million (ppm) is 1 milligram in 1 liter i.e. 1 mg/L or 1 microgram in 1 mL i.e. 1 µg/mL Scientist sometimes write this as 1 µg mL-1 A part per billion (ppb) is 1 µg L-1 Concentration is the relative amount 1000 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 As 49 mg 21 bathtubs contain 21 x 233 L = 4,900 L 1 grain in 21 bathtubs = 10 ppb The US EPA limit for arsenic in drinking water

13 Arsenic speciation There are a lot of different arsenic compounds in the environment. Inorganic Arsenic bonded to oxygen and/or sulfur or hydrogen. As2O5 H3AsO4 arsenate As2O3 H3AsO3 arsenite AsH arsine Organic Arsenic bonded to carbon and/or oxygen or hydrogen Methylated arsenate CH3AsO(OH) MMA (CH3)2As(O)OH DMA Arsenobetaine, arsenocholine

14 Some formulae for the chemists in the audience.
arsenate monomethylarsonate arsenite The 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 methylarsonate cacodylate dimethylarsinate trimethylarsine oxide

15 More formulae for the chemists in the audience.
trimethylarsine oxide tetramethylarsonium

16 Yet more formulae for the chemists in the audience.
TETRA arsenobetaine Pictures 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 arsenic arsenocholine

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 arsenosugars seafood arsenic Some arsenic compounds are toxic Acute 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-toxic Monomethyl and dimethyl arsenates The 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 forms Drinking water contains toxic, inorganic forms Food 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 problem If more than guideline value: more analysis needed Asking 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 2010 The 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 stage Weight lbs 1 lb = 0.45 kg Tolerable daily intake µg Newborn 7 9 1-year-old 22 30 5-year-old 42 57 teenager 140 (m) 117 (f) 191 (m) 160 (f) young adult 155 (m) 127 (f) 211 (m) 173 (f) Adult (US average) 191 (m) 164 (f) 260 (m) 224 (f) football player 300 409 overweight your call > 400 Acute lethal dose (adult) 100 mg

23 Tolerable daily intake µg Acute lethal dose (adult) 100 mg
How much inorganic arsenic do we actually eat? Food: Ask the analytical chemists. Developmental stage Weight lbs 1 lb = 0.45 kg Tolerable daily intake µg Newborn 7 9 1-year-old 22 30 5-year-old 42 57 teenager 140 (m) 117 (f) 191 (m) 160 (f) young adult 155 (m) 127 (f) 211 (m) 173 (f) Adult (US average) 191 (m) 164 (f) 260 (m) 224 (f) football player 300 409 overweight your call > 400 Acute 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 finfish 2,400 0.5 shrimp 1,900 2 tuna 512 1 rice 303 74 chicken 86 grape juice 58 9 beef 52 0.4 peanut butter 44 5 watermelon 40 flour 39 11 spinach 6 apple juice 8 3 Moisture 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 Data Scientists at US EPA, National Taiwan University, and the Environmental and Occupational Health Sciences Institute Inorganic arsenic. 12 11 24 NHANES is National Health and Nutrition Examination Survey. 18 17 13 5

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 American weighs 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 day Age Number Average 5th percentile 99th percentile 0 - 1 757 0.62 0.05 2.08 1 - 2 1,068 0.54 5.06 3 -5 963 0.03 5.6 6-12 2,190 0.37 0.02 4.28 13 -19 3,576 0.25 0.01 3.58 4,221 0.33 4.12 >50 3,804 0.32 4.91 All 16,931 0.36 4.45 Remember 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 day Age Number Average 5th percentile 99th percentile 0 - 1 757 0.23 0.01 0.8 1 - 2 1,068 0.1 0.59 3 -5 963 0.08 0.4 6-12 2,190 0.04 0.25 13 -19 3,576 0.03 0.21 4,221 0.28 >50 3,804 0.22 All 16, 931 0.05 0.41 The 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 arsenic µg kg-1 wet weight Inorganic arsenic rice 303 74 Total arsenic Inorganic MMA DMA I + MMA + DMA % missing 335 55 ND 84 218 62 61 123 44 462 81 3 202 286 38 196 97 2 99 198 There’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 Cincinnati The 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. Date Location Total Inorganic % missing* LA 167 105 -9 AR 184 79 -11 TX 445# 111 CA 62 61 -33 AVE US 202 90 -13 264 98 The 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-1 Location Average Total Max total Average inorganic Max inorganic Bangladesh 130 330 80 210 China 140 460 160 380 Egypt 50 580 No data France 280 560 India 70 180 30 Italy 150 110 Japan 190 420 Spain 200 820 Thailand 390 USA 250 660 100 No 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, 2011 Proceedings of the National Academy of Sciences of the USA Dec 5th 2011 Rice consumption contributes to arsenic exposure in US women Diane 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%.

39 So. What about apple juice?

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 L i.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.


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