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How Much Arsenic Do We Eat? Analytical chemists make light work in tracking potentially harmful chemicals. Julian Tyson Department of Chemistry UMass Amherst. Analytical chemists provide information about the chemical composition of materials. So that a decision can be taken. - PowerPoint PPT Presentation
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How Much Arsenic Do We Eat?
Analytical chemists make light work
in tracking potentially harmful chemicalsJulian Tyson
Department of Chemistry
UMass Amherst
Analytical chemists provide information about the chemical composition of materials. So that a decision can be taken.
Interaction of light with materials.
How do analytical chemists make light work in tracking potentially
harmful chemicals?
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
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.
Analytical chemists use the interaction of light with with molecules that contain arsenic to measure the arsenic in relevant materials.
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 1 - 4 ppb
River and surface water: about 0.1 - 1 ppb
Realgar As4S4
Arsenic trioxide As2O3 Arsenic As
Orpiment As2S3
The arsenic in the environment story
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
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.
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 liter
A drop (of water) is about 50 µLA bathtub contains about 230 L
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
1000 ppb = 1 ppm
One grain weighs 65 mg(2.5 mm cube of As2O3)76% by weight is As49 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
How to make a 10 pbb solution
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 arsenateAs2O3 H3AsO3 arseniteAsH3 arsine
Organic
Arsenic bonded to carbon and/or oxygen or hydrogen
Methylated arsenate
CH3AsO(OH)2 MMA(CH3)2As(O)OH DMA
Arsenobetaine, arsenocholine
Some formulae for the chemists in the audience.
arsenite
dimethylarsinate
arsenate monomethylarsonate
cacodylate
trimethylarsine oxide
More formulae for the chemists in the audience.
trimethylarsine oxide tetramethylarsonium
Yet more formulae for the chemists in the audience.
arsenocholine
Seafood arsenic
TETRA
arsenobetaine
Not all arsenic compounds are very toxic
Some arsenic compounds are “non-toxic.”arsenobetaine and arsenocholine and arsenosugarsseafood arsenic
OK - all chemicals are toxic: it all depends on the dose and how you interact with them.
Some 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 arsenates
The adverse health effect of concern is cancer.
How does arsenic get into our food? Plants take up arsenic compounds from the soil. Legacy of previous applications.
How arsenic gets into crops
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
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 http://www.who.int/foodsafety/chem/summary72_rev.pdf
The limit for dietary inorganic arsenic exposure is:
3.0 µg per kg body weight per day
How much inorganic arsenic is considered safe?Dietary: 3.0 µg per kg body weight per day.
Developmental stage
Weight lbs1 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
How much inorganic arsenic do we actually eat?Food: Ask the analytical chemists.
Developmental stage
Weight lbs1 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
Food and Chemical Toxicology 37 (1999) 839-846
Examined 40 commodities expected to deliver 90% of total dietary inorganic arsenic. Took 4 samples of each. Measured total arsenic and inorganic arsenic.
A market basket survey of inorganic food in rice
Food Total arsenic µg kg-1 wet weight
Inorganic arsenicµg kg-1 wet weight
saltwater finfish 2,400 0.5
shrimp 1,900 2
tuna 512 1
rice 303 74
chicken 86 1
grape juice 58 9
beef 52 0.4
peanut butter 44 5
watermelon 40 9
flour 39 11
spinach 5 6
apple juice 8 3
Inorganic arsenic.
Environmental Health Perspectives, 2010, 118, 345-350
Probabilistic modeling of dietary arsenic exposure and dose and evaluation with 2003-2004 NHANES Data
Scientists at US EPA, National Taiwan University, and the Environmental and Occupational Health Sciences Institute
24
12
1718
13
11
5
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. 1.96 µg per day.
Approximately 10% of exposure from food is the toxic inorganic form of arsenic.
The average American weighs 40 kg i.e. 88 lbs.
Age Number Average 5th percentile
99th percentile
0 - 1 757 0.62 0.05 2.08
1 - 2 1,068 0.54 0.05 5.06
3 -5 963 0.54 0.03 5.6
6-12 2,190 0.37 0.02 4.28
13 -19 3,576 0.25 0.01 3.58
20 - 49 4,221 0.33 0.01 4.12
>50 3,804 0.32 0.01 4.91
All 16,931 0.36 0.01 4.45
Calculated exposure from food. Total 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 0.01 0.59
3 -5 963 0.08 0 0.4
6-12 2,190 0.04 0 0.25
13 -19 3,576 0.03 0 0.21
20 - 49 4,221 0.03 0 0.28
>50 3,804 0.03 0 0.22
All 16, 931 0.05 0 0.41
Calculated exposure from food. Inorganic arsenic: µg per kg body weight per day
Food Total arsenic µg kg-1 wet weight
Inorganic arsenicµg kg-1 wet weight
rice 303 74Total
arsenicInorganic MMA DMA I + MMA +
DMA%
missing
335 55 ND ND 55 84
218 62 ND 61 123 44
462 81 3 202 286 38
196 97 2 99 198 0
There’s a problem with the Schoof analysis of the rice.
The Schoof report: A market basket survey of inorganic food in rice
What do other researchers find about arsenic in rice?
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.
Food Additives and Contaminants: Part B, 2009, 2, 112-120
Date Location Total Inorganic % missing*
1980-81 LA 167 105 -9
1980-81 AR 184 79 -11
1980-81 TX 445# 111 0
1980-81 CA 62 61 -33
1980-81 AVE US 202 90 -13
2001-02 AVE US 264 98 -11
#One sample had over 1000 µg kg-1 total: inorganic 150 µg kg-1
All values in µg kg-1 based on dry weight.
*The minus sign means that the sum of I + MMA + DMA > total
“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.”
Heitkemper and colleagues at US FDA Cincinnati
Conclusions
What do other researchers find about arsenic in rice?
Meharg and colleagues at the University of Aberdeen
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 No data
France 280 560 No data No data
India 70 180 30 70
Italy 150 330 110 160
Japan 190 420 No data No data
Spain 200 820 No data No data
Thailand 140 390 No data No data
USA 250 660 100 150
“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.”
Meharg and colleagues at the University of Aberdeen
Conclusions
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.”
www.pnas.org/cgi/doi/10/.1073/pnas1109127108
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%.
So. What about apple juice?
88 samples purchased in Aug and Sept 2011 in CT, NJ, and NY.
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.
30 - 60 µg for young children.
Need to drink 1.2 – 2.4 L
i.e. 2.5 – 5 pints per day.
Take digital picture with digital camera.