Hello,

Your equation is described in this paper:

http://www.biomedsearch.com/attachments/00/23/23/43/23234365/1752-153X-6-156.pdf

The term Reference Dose (RfD) is used by the U.S. Environmental Protection Agency and it is a measure of daily exposure that should not be associated with non-cancer adverse effects. (Kind of like an ADI)

The THQ has been used to assess metal exposures from soil or vegetable ingestion. It is unitless or more precisely mg/mg if the values are entered into the equation correctly and in the proper units. Basically if the top of the equation (EF x FD x DIM) is a smaller value than the bottom of equation (RfD x W x T) then the exposure to metals from the source (e.g., vegetables) is less than the dose (adjusted Reference Dose) determined not be associated with non-cancer adverse effects.

As stated in the paper "A small value of the index (

Thank you, but the picture is still not clear to me. Let i simplify my problem. Lets say i go for sampling the vegetable from heavy metal polluted area and tested for metals say Fe, Cu, Zn, Ni, Co, Mn, Cr and Zn. Now i want to calculate the THQ by this formula which is mentioned in the question. Now the question is what value should i take as EF is it 365 days of the year or i just make a survey to ask how often they make vegetables. Other questions are similar like what will be the FD and how will i calculate DIM? Let me know if these values are fixed by EPA or any other agency that usually an average person eat this much which i undertake for calculation. Is the value of RfD is fixed by EPA. Just we calculate for 65kg as the average weight and T as 365 days.

I shall be highly obliged if you clarify this to me.

In breaking down the equation I would think EF, exposure frequency, to be the number of days per week a person might eat the vegetables. The FD or exposure duration should then equal perhaps the number of weeks that the vegetables are available (if limited by growing season, but consider preserved foods too) times number of years in area. FD and T must be in line with each other so that the results make sense. Number of exposure years needs to be considered for metals even for a non-cancer response (RfD) due to the potential for accumulation.

DIM would be amount of vegetable eaten per day (typical serving size) x concentration of metal in vegetable. e.g. 300 ppm (mg/kg) metal/vegetable x 0.200 kg of vegetable/day = 60 mg/day (numbers are just out of the air). - but if more than one type of vegetable is grown in the same heavy metal polluted soil, you have to calculate total daily metal exposure from all vegetables. It may help to have a computer model.

Some RfD values can be found here: http://cfpub.epa.gov/ncea/iris/index.cfm?fuseaction=iris.showSubstanceList. If EPA has not derived an RfD you may be able to substitute in a similar meaning value (e.g., acceptable daily intake-ADI; tolerable daily intake-TDI; upper limit - UL) from other authoritative bodies (e.g., JECFA, WHO, IOM)

If we assume zinc is present in carrots at 300 mg/kg and the serving size for carrots is 200g the DIM for zinc is 60 mg/day (assuming carrots are the only vegetable eaten from polluted area); the EPA RfD for zinc is 0.3 mg/kg/day; EPA typically uses a body weight of 60 kg for females and 70 kg for males (you could adjust the bw estimate based on your population group). Assume the time a female spent living in one area is 10 years and she eats carrots 5 days/week for 12 weeks/year)

THQ = E F x F D xDIM ∕ RfDxWxT

THQ = (5 days/week) x [(12 weeks/year x 10 years)] x 60 mg/day / 0.3 mg/kg/d x 60 kg x [365 d/year x 10 years] = 36,000 mg/65,700 mg = 0.5

For more advice and to confirm my understanding of this equation, I would suggest contacting some of the authors of the Gergen and Harmanescu paper or contacting the EPA directly.

Best Regards

Thank you, it is quite helpful.

You're welcome. Note that any results should also be considered in comparison to normal background levels of metals in control soils.

Best Regards

For Mehjabeen Javed:

The theoretical aspect has already been very nicely explained by Lois A Haighton . I have tried my humble on only the experimental part. I really appreciate your research project with is a well blend of both Chemistry/ Zoology.

An experimental method to calculate THQ experimentally is explained as:

[A] Procure vegetables from three sites ( Rural, Urban and Semi-)

[B] Classify the vegetables as root(Parsley, Carrot, Onion etc), Leafy( Cabbage,Lettuce etc ) and fruity(Cucumber, Green beans etc )

[C]* (i)For Root vegetables (Cu =1-4 mg/ Kg; Zn= 10-50 mg/ Kg; Cd = 0.1-0.27 mg/ Kg and Pb= 1-5.5 mg/ Kg fresh matter . (ii)For leafy vegetables Cu------reported in literature),Zn=(--reported in literature) Cd =2-10 mg/ Kg dry matter) and Pb =40-250 mg/ Kg dry matter) etc----etc.,

(iii)Fruit vegetables -Pb (0.6 mg/ Kg fresh matter) and Cd around 0.1 mg, Kg fresh matter etc ---etc (reported in literatre)

*Pls. note that are these values reported in literature for different countries. But you have to experimentally determine the values of these metal contents in the types of vegetables you want to investigate. In the present method of calculation, I have taken the values to be the average of the two reported extremes.

[D]. Oral reference doses (RfD) (mg/ Kg/ day) for elements reported in literature:

Fe (0.700 ), Mn (0.014), Zn (0.300), Cu( 0.040), Ni (0.020) ,

Cd( 0.001), Pb (0.0035).

[E].The average body weight assumed is Wmale = 68 Kgand Wfemale = 60 Kg.

[F].THQ = EFxFDxDIM/RfDxWxT

(i) EF is exposure frequency;

(ii)FD is the exposure duration,

(iii)DIM is the daily metal ingestion (mg/ person/

day ) and is calculated as:

DIM = Daily fresh food ingestion (Kg/ person/ day)

× Metal content (mg/ Kg fresh matter).

(iv) RfD is the oral reference dose (mg/ Kg/ day)

(v)W is average body weight(Kg)

(vi) T is the average exposure timeage exposure time for noncarcinogens (365 days/ year× number of exposure years).

(vii)Here EF was setup at 122days/ year(eat each one the thee kinds of vegetables on every third day)

(viii) Length of exposure (FD) was set to 65 for males and 68 for females based on the average life expectancy in India,starting from 8 years of age .

[G] In a way we should calculate Three sets of values- ONE for the MALES at Rural. Urban an Semi Places and SECOND set for FEMALES at the same places.

But due to the paucity of space/ time, I try only ONE SET for MALES and the OTHER SET for the FEMALES. Also, I include ony TWO METALS ( the most toxic-Cd, Pb) to explain the method while the results for other metals can be similarly calculated.

(ix) We assume the on the average MALE takes 150 g (0.15 Kg) and the FEMALE takes 120g (0.12 Kg) per day of Root, Leafy and Fruit vegetable on every third day.

[H] MALE- (ROOT Vegetables)

THQ(Cd)=122. (68-8). 0.185. (0.15) /0.001.68.365.(68-8)=0.136

THQ(Pb)=122. (68-8). 3.25. (0.15) /0.0035.68.365.(68-8)=0.684

FEMALE- (ROOT Vegetables)

THQ(Cd)=122. (68-8). 0.185. (0.12) /0.001.68.365.(68-8)=0.0984

THQ(Pb)=122. (68-8). 3.25. (0.12) /0.0035.68.365.(68-8)=0.547.

hello

Is it possible to know, if exist a Rfd (reference dose /day)(guidlines ) about toxic metals in soil (ingestion) and food (leaf and corn)

Rfd for metals remains constant whether it is from vegetables, non vegetable sources, soil etc.

Hi Lois A Haighton

On a similar problem, I have been searching for RfD for sulfamethoxazole and oxytetracycline antibiotics.

Any help will be appreciated!!

you can search usepa guidelines

I searched but did not find RfD for sulfamethoxazole and oxytetracycline antibiotics.

What are the oral reference doses (RfD(s)) for

1. Rubidium

2. Titanium

3. Zirconium

4. Thorium

Hi

dear Mehjabeen Javed

I'll send you all the formulas in one file.

Hope it works for you