Pioneer Valley STEM Network Out of School Time Program The arsenic project themes Julian Tyson Department of Chemistry [email protected].

Pioneer Valley STEM Network

Out of School Time Program

The arsenic project themes

Julian Tyson

Department of Chemistry

[email protected]

Pioneer Valley STEM Network

Out of School Time Program

The arsenic project themes

Joining Professor Tyson’s research group and investigating aspects of arsenic compounds in the environment and our food and drink.

I’m expecting to get results in the form of scientific report and I’m available for consultation (e-mail: [email protected])

Mandal and Suzuki, “Arsenic around the world” Talanta, 2002, 58, 201-235. (example of review article).As, element 33, a mono-isotopic (75) metalloid, named for the yellow pigment orpiment (Latin arsenicum), probably isolated in 1250 by Albert Magnus.

It is widely distributed in all environments. “50th most abundant in earth’s crust, 26th in seawater and, 31st in the body” (numbers in article are wrong).

Concentrations. In rocks: 2 mg kg-1, slightly higher in soils. In sea water: 8 µg L-1. But there is a huge range.

Background to “The Arsenic Project”

Scientists use the name of the element as a shorthand for “relevant compounds of the element.”

Realgar As4S4Arsenic trioxide As2O3

Arsenic AsOrpiment As2S3

Mandal and Suzuki, “Arsenic around the world” Talanta, 2002, 58, 201-235.

Uses (past and present): insecticide, herbicide, wood preservation, embalming, poison, chemical warfare agent, bullets, desiccant (cotton production), feed additive, fireworks, medicine, electronics, glass, paints, wallpapers, and ceramics.

Background to “The Arsenic Project”

The US no longer produces arsenic, but imports all it needs. In 2005, US imported 812 tons of elemental arsenic and 8300 tons of arsenic trioxide.

Intake of 70 to 300 mg of arsenic trioxide may be fatal.

Death typically occurs between 12 to 48 hours but can occur within one hour. Those who survive arsenic trioxide poisoning may develop encephalopathy* or severe peripheral neuropathies.

Symptoms of acute poisoning usually occur within one hour of ingestion but may be delayed for up to 12 hours, particularly in the presence of food.

The principle toxic effects are hemorrhagic gastro-enteritis, profound dehydration, cardiac arrhythmias, convulsions, muscle cramps, shock and death.

*any diffuse disease of the brain that alters brain function or structure

Hot spots exist in:Argentina, Australia, Bangladesh, Chile, China, Hungary, India, Mexico, Mongolia, Peru, Thailand and the United States of America

Adverse health effects documented in:Bangladesh, China, India (West Bengal), Taiwan, and the United States of America, and 10 other countries (because of water),

Arsenic in drinking-water in Bangladesh will cause 200,000 – 270,000 deaths per year from cancer.Arsenic contaminated water revealed in 1993. 4.5 million tube wells. Arsenic contamination in 20% of those tested.

Intakes of higher amounts of arsenic on a chronic basis may cause hyperkeratosis, especially of the palms and soles, skin pigmentation, eczematous or follicular dermatitis,

Leading eventually to various cancers, such as basal cell carcinoma and bladder, liver and lung cancers.

Environmental Health Perspectives, 2005, 113, A379

Ryker, S.J., Mapping arsenic in groundwater: Geotimes, 2001, 46, 34-36.

Locations of wells and concentrations of arsenic in water from bedrock aquifer wells in New England.

The concentration data are shown with circles sized by concentration ranges.

J. D. Ayotte et al., Arsenic in Groundwater in Eastern New England: Occurrence, Controls, and Human Health Implications. Environmental Science & Technology, 2003, 37, 2075-2083

No. of samples = 2470

Recent studies estimate that 2-100 children per million exposed to PTW during early childhood may develop lung or bladder cancer later in life as a result of this exposureConsumer Product Safety Commission (2003)

Many foods and drinks contain arsenic above the detection capabilities of modern chemical analysis instruments.

How much do we eat? How much is safe?

There’s a complication (or two):

Seafood contains the highest concentration of arsenic up to 2400 mg kg-1.

The arsenic compounds vary from one food to another.

The arsenic compounds vary in their toxicity.

The compounds in seafood are “non-toxic.” The arsenic compounds in everything else are more or less toxic.

How arsenic gets into rice.

Arsenic compounds commonly encountered in environmental materials and in our food.

H3AsO3 arsenous acid

H3AsO4 arsenic acid

CH3AsO3H2 monomethylarsonic acid

(CH3)2AsO2H dimethylarsinic acid aka cacodylic acid

(CH3)3AsO trimethylarsine oxide

(CH3)4As+ tetramethylarsonium

(CH3)3As+CH2CO2- arsenobetaine

(CH3)3As+CH2CH2OH arsenocholine

November 2012

Eat 45 g of the Lot 3 Rice Select material: how much total arsenic did you eat? How much inorganic arsenic?

Concentration. (a key concept)Solids: mass fraction x scaling factor

Several different ways of expressing this ratio. Convert the masses to the same units and express the resulting fraction as parts per hundred parts (pph), parts per million parts (ppm), or even parts per billion parts (ppb).

The second “parts” is omitted from the expression.

Concentrations in ppb: the quick route.Strategy: Choose mass units that make the multiplication by one billion easy.

Mass of arsenic = m gMass of rice = M g

Concentration = (m/M) x 109 = m x 109/M

If m were expressed in ng

Concentration = (m x 10-9/M) x 109 = m/Mi.e. 1 ppb = 1 ng in 1 g = 1 ng g-1

Concentrations in ppb: the quick route.

Look at another possibilities.

Mass of arsenic = m µgMass of rice = M kg

Convert masses to g

Concentration = (m x 10-6 /M x 103 ) x 109 = m/M

i.e. 1 ppb = 1 ng in 1 g = 1 ng g-1

= 1 µg in 1 kg = 1 µg kg-1

Concentration.

A student in my lab determined the amount of arsenic in a brown rice sample, then removed the husk and determined the amount in the “polished” white rice. What are the concentrations?

Sample Mass g Arsenic content µg

Concentration of arsenic in

ppb

Brown 450 390 ?White 250 140 ?

Eat 45 g of the Lot 3 Rice Select material: how much total arsenic did you eat? How much inorganic arsenic?

Concentration.

917 ppb is 917 g per 109 g (109 is giga, G)917 ppb is 917 mg per 106 g (106 is mega, M)917 ppb is 917 µg per 103 g (103 is kilo, k)917 ppb is 917 ng per g

m, milli, is 10-3 µ, micro, is 10-6 n, nano, 10-9

Eat 45 g of rice containing 917 ppb arsenic, i.e. 917 ng per g.

Mass arsenic eaten = 917 x 45 ng = 41,265 ng

= 41,265/1000 µg = 41 µg (round to 2 digits).

Concentration.

Total arsenic content is 917 ppbMass arsenic eaten = 45 x 917 ng = 41,265 ng= 41,265/1000 µg = 41 µg.

Inorganic content is 102 ppb. So in 45 g of the rice there is ??? µg of inorganic arsenic.

“Inorganic” means H3AsO3 (arsenous acid) and H3AsO4 (arsenic acid).

“Organic” means compounds of carbon, oxygen, hydrogen, and other elements.

Arsenic compounds commonly encountered in environmental materials and in our food.

H3AsO3 arsenous acid

H3AsO4 arsenic acid

CH3AsO3H2 monomethylarsonic acid

(CH3)2AsO2H dimethylarsinic acid aka cacodylic acid

(CH3)3AsO trimethylarsine oxide

(CH3)4As+ tetramethylarsonium

(CH3)3As+CH2CO2- arsenobetaine

(CH3)3As+CH2CH2OH arsenocholine

Percent of inorganic arsenic?

Calculate the “percent of inorganic arsenic.”

Note (a) this does NOT mean the percent of inorganic arsenic in the rice (214 ppb = 214 x 10-7 pph = 2.14 x 10-5 %)

(b) that the information given is the concentration of the total arsenic and the concentration of the inorganic arsenic.

How to proceed?

Percent of inorganic arsenic?

Calculate the “percent of inorganic arsenic.” i.e. the percentage of the total arsenic that is inorganic arsenic.

Take 1 kg of rice then mass of total arsenic is 398 µg and mass of inorganic arsenic is 214 µg.

Mass fraction inorganic arsenic = 214/398

pph = 100 x 214/398 =53.7688442 = 53.8%

Percent of inorganic

arseni

Why do the numbers not agree?

My guess is that it is the result of rounding. If the numbers were 398.2 and 213.7 the answer would be 53.6664992 pph.

i.e. 53.7 %.

What is the concentration of arsenic in rice?

Quarter cup of rice and two cups of water. Boil to extract all the arsenic. Measure the arsenic concentration in the solution (50.0 ppb).

Concentration in solution: mass/volume fraction multiplied by scaling factor.

1 ppb = 1 µg per L = 1 ng per mL

For dilute solutions 1 L weighs 1 kg

What is the concentration of arsenic in rice?

Quarter cup of rice and two cups of water. Boil to extract all the arsenic. Measure the arsenic concentration in the solution (50.0 ppb).

Need to know the mass of arsenic and the mass of the rice (then, fix the units and calculate).

What is the concentration of arsenic in rice?Quarter cup of rice and two cups of water. Boil to extract all the arsenic. Measure the arsenic concentration in the solution.

Concentration of arsenic in solution = 50.0 ppb

= 50.0 ng mL-1

Volume of water added was 2 cups = 473.2 mL.

1 US cup = 236.6 mL

0.25 cup = 59.2 mL

What is the concentration of arsenic in rice?Quarter cup of rice and two cups of water. Boil to extract all the arsenic. Measure the arsenic concentration in the solution.

Concentration of arsenic in solution = 50.0 ppb

= 50.0 ng g-1

Mass of arsenic is (50 x 473.2) ng = 23,660 ng

Mass of rice? Know the volume (0.25 cups = 59.15 mL). Need to know the density (mass per unit volume). Can be found from a separate experiment, but need a balance. But need to account for the spaces between the grains.

What is the concentration of arsenic in rice?Quarter cup of rice and two cups of water. Boil to extract all the arsenic. Measure the arsenic concentration in the solution (100 ppb).

Mass of arsenic is (50 x 473.2) ng = 23,660 ng

Mass of rice? Know the volume (0.25 cups = 59.15 mL). Density of rice is 1.45 g mL-1

But only 55% of volume is rice (45% is spaces between grains). “Density” is 0.55 x 1.45 = 0.98

So, mass of rice = 47.2 g

Conc of arsenic = 23,660/47.2 = 502 ng g-1

Analytical chemistry

Some basic concepts:Qualitative analysis: perform some diagnostic chemistry and compare what happens with result for authentic material (may be in memory). Detect inorganic arsenic by formation of colored product with mercuric bromide exposed to arsine vapor formed by reaction of inorganic arsenic with zinc in acid solution.

Gutzeit – Marsh test.

Analytical chemistry

Some basic concepts:Quantitative analysis: (a) perform some chemistry and measure the extent of the reaction.(b) perform some chemistry and compare the extent of the reaction with that of authentic material of known concentration of analyte(s).

Authentic material of known concentration of analyte(s) is a standard. A standard with no analyte is a blank.

Analytical chemistry

(b) perform some chemistry and compare the extent of the reaction with that of authentic material of known concentration of analyte(s).

This is usually done with an instrument (not a machine). Instrumental analysis involves measuring the response to standards, establishing the underlying relationship between instrument response and concentration and applying this to the response of the sample(s). The process is called calibration.

Is usually performed at the time of analysis.

Analytical chemistry

The process is called calibration.Is usually performed at the time of analysis.

Instrumentresponse

Concentration of analyte

Rx

Cx

Analytical chemistryInstrumentresponse

Concentration of analyte

Rx

Cx

The underlying relationship is often a straight line. But sometimes a curve is a better fit.Often does not pass through 0,0. That is there is a measurable response to the blank.Reagents are contaminated with analyte.

00

Analytical chemistry

Some basic concepts:Detection Limit: the lowest concentration that can be measured with a given confidence (usually about 95% percent). Abbr. LOD or DL.

Analytical chemists still debate/argue over how to measure LODs. Often done by measuring the response to a standard of low concentration (maybe the blank) and calculating the concentration that gives a signal equal to three times the standard deviation of that signal.

Analytical chemistry

Some basic concepts:Limit of quantification: the lowest concentration that can be measured with a reasonable uncertainty. Abbr. LOQ.

Usually defined as concentration giving an instrument response 10-times the standard deviation of the response to the blank.

Dose-response relationships

Toxicology is the study of the adverse effects of chemicals on living organisms. It involves the study of symptoms, mechanisms, treatments and detection of poisoning, especially of people.

Animal responseExcess lifetime risk of getting a cancer

Dose Mass of chemical per mass of animal per time.

Dose-response relationships. Toxicology

Inorganic arsenic is a non-threshold carcinogen

Animal responseExcess lifetime risk of getting a cancer. Usually expressed as a decimal fraction: 1 in 10,000 i.e.0.0001 Dose. mass of chemical per mass of

animal per time. Usual units (for arsenic) are: µg per kg body weight per day

Dose-response relationships. Toxicology

Inorganic arsenic is a non-threshold carcinogen

Response. Excess lifetime risk of getting a cancer.

Dose. µg per kg body weight per day

0.0001

D

Slope = 3.67 (mg/kg-d)-1

Calculate D. 0.0001/D = 3.67 (mg/kg-d)-1

D = 0.0001/3.67 = 2.725 x 10-5 x 1000 µg/kg-d = 0.027

Dose-response relationships. ToxicologyDose. µg per kg body weight per day

D = 0.027 µg per kg body weight per day

If you weigh 175 lb (80 kg, as 1 kg = 2.2 lb)“Safe” to consume 0.027 x 80 = 2.2 µg of inorganic arsenic

per day

I L of water at the USEPA maximum of 10 µg L-1 delivers a dose of 10 µg i.e. about 5-times as much as the safe limit, and so corresponds to a risk of about 5 in 10,000 (half way down page 4396).

Eat 45 g of the Lot 3 Rice Select material: how much total arsenic did you eat? How much inorganic arsenic?

Dose-response relationships. ToxicologyDose. µg per kg body weight per day

D = 0.027 µg per kg body weight per day If you weigh 80 kg, it is “safe” to consume 0.027 x 80 = 2.2 µg of inorganic arsenic per day.

A 45-g serving of rice containing 100 ppb of inorganic arsenic delivers (100 x 45)/1000 µg = 4.5 µg. If you have 2 servings per week and you weigh 80 kg your dose is(4.5 x 2)/ (7 x 80) = 0.016 µg per kg body weight per day.

i.e. within the safe limit

Dose-response relationships. ToxicologyDose. µg per kg body weight per day

D = 0.027 µg per kg body weight per day If you weigh 80 it is “safe” to consume 0.027 x 80 = 2.2 µg of inorganic arsenic per day.

A 45-g serving of rice containing 100 ppb of inorganic arsenic delivers (100 x 45)/1000 µg = 4.5 g. If you have 2 servings per week and you weigh 80 kg your dose is(4.5 x 2)/ (7 x 80) = 0.016 µg per kg body weight per day.

i.e. within the safe limit

Consumer Reports November 2012

Dose-response relationships. ToxicologyDose. µg per kg body weight per day

D = 0.027 µg per kg body weight per day If you weigh 80 it is “safe” to consume 0.027 x 80 = 2.2 µg of inorganic arsenic per day.

A 45-g serving of rice containing 100 ppb of inorganic arsenic delivers (100 x 45)/1000 µg = 4.5 g. If you have 2 servings per week and you weigh 80 kg your dose is(4.5 x 2)/ (7 x 80) = 0.016 µg per kg body weight per day.

i.e. within the safe limit

Consumer Reports November 2012