# What is the half-life of the following chemical compounds?



## earthfrog (May 18, 2008)

Any objective chemists in the house?
I am looking for info on the half-life of bifenthrin, imidacloprid and metaldehyde as these are the chemicals that are often used on commercial plants in nurseries. I was told by Costa Farms, the major supplier of Lowe's and Home Depot's plants that one used was 'metachloroprid' but that is not turning up. Specifically, if anyone is able to specify the half-life of these things in plants or frogs, that is ideal.

Thanks!


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## frogparty (Dec 27, 2007)

Look it up in the Merc or CRC online. All chemicals and their properties


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## Chris155hp (Mar 17, 2010)

bifenthrin has a half life from about 34 days not to sure about the other ones but my dad is a Horticulturalist so he might know. I could give him a call tom and let you know. But im sure a google search will be much faster


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## earthfrog (May 18, 2008)

frogparty said:


> Look it up in the Merc or CRC online. All chemicals and their properties


Thanks. Would you be able to provide me with some links?


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## Chris155hp (Mar 17, 2010)

earthfrog said:


> Any objective chemists in the house?
> I am looking for info on the half-life of bifenthrin, imidacloprid and metaldehyde as these are the chemicals that are often used on commercial plants in nurseries. I was told by Costa Farms, the major supplier of Lowe's and Home Depot's plants that one used was 'metachloroprid' but that is not turning up. Specifically, if anyone is able to specify the half-life of these things in plants or frogs, that is ideal.
> 
> Thanks!


 FYI Costa Farms Is my dads main competition down in miami and they spray a tun of pesticides so be careful and clean them well. lol not to bash them but i just thought it was funny. what a small world


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## earthfrog (May 18, 2008)

Chris155hp said:


> FYI Costa Farms Is my dads main competition down in miami and they spray a tun of pesticides so be careful and clean them well. lol not to bash them but i just thought it was funny. what a small world


No problem. Costa also uses the others I listed in the first post--it took a bit of calling to get that info. So, does your dad's company not use a lot of pesticides, or systemics? Do they supply major retail stores? If so, please share as I am looking for less of a hassle when quarantining plants for the vivarium.


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## Chris155hp (Mar 17, 2010)

earthfrog said:


> No problem. Costa also uses the others I listed in the first post--it took a bit of calling to get that info. So, does your dad's company not use a lot of pesticides, or systemics? Do they supply major retail stores? If so, please share as I am looking for less of a hassle when quarantining plants for the vivarium.


Sadly yes. Pretty much all major south florida nurseries do. Way to many harmful insects. But even if he didnt he mainly grows larger plants like hibiscus and palms, not something we can use in our tanks (trust me i have been around the farm looking for plants to put in my viv) And the only reason i respond to one was bc thats the only one i knew what i was talking about.


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## earthfrog (May 18, 2008)

OK, got some additional info finally for those wishing to delve deeper into pesticides commonly used on tropical plants. 



> Half-life is the period of time it takes for a substance undergoing decay to decrease by half. Half-life is defined in terms of probability. It is the time when the expected value of the number of entities that have decayed is equal to half the original number. For example, one can start with a single radioactive atom, wait its half-life, and measure whether or not it decays in that period of time. Perhaps it will and perhaps it will not. But if this experiment is repeated again and again, it will be seen that it decays within the half-life 50 percent of the time.


 _from wikipedia_

Info on metaldehyde (snail bait):
Metaldehyde - toxicity, ecological toxicity and regulatory information

The aerobic soil half-life of metaldehyde is 67 days, and the anaerobic soil half-life is 223 days. (Aerobic refers to exposure to air, and anaerobic means without air exposure). This means it may fully break down in 134 days in air, and in 446 days in the soil. 

Info (below) on bifenthrin (Brand name Talstar), commonly used as a surface insecticide. Note that time quarantine is relevant because some insecticides are not easily removed with soap and water.

Bifenthrin - toxicity, ecological toxicity and regulatory information

The aerobic soil half-life of bifenthrin is 95 days. The anaerobic soil half-life is not listed. This means when exposed to air, bifenthrin breaks down in 190 days. 

[I could not find a reference for what was quoted to me by Costa Farms as 'metachloroprid', the systemic insecticide, so instead I am referencing imidacloprid since it is also widely used as a foliar spray. 
If anyone has any ideas on what the name 'metachloroprid' actually refers to, please post it here.] 

Info on imidicloprid:
Imidacloprid - toxicity, ecological toxicity and regulatory information

The aerobic soil half-life is 997 days. The anaerobic soil half-life is only 27 days, so this one seems to have less overall risk than the others in terms of affecting beneficial organisms deeper within the soil and subsequently frogs.


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## phender (Jan 9, 2009)

earthfrog said:


> OK, got some additional info finally for those wishing to delve deeper into pesticides commonly used on tropical plants.
> 
> The aerobic soil half-life of metaldehyde is 67 days, and the anaerobic soil half-life is 223 days. (Aerobic refers to exposure to air, and anaerobic means without air exposure). This means it may fully break down in 134 days in air, and in 446 days in the soil.


That is not what I understand half-life to mean, unless it is used differently in pesticides.
In 67 day half will be gone, after 67 more days half of what was left is gone, so there is still a quarter of it left. After another 67 days you would still have an 1/8 of it still left. Its sort of like continually cutting a number in half. You never actually get to zero, except when you are talking about chemicals there is a last molecule that eventual breaks down.


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## McBobs (Apr 26, 2007)

phender said:


> That is not what I understand half-life to mean, unless it is used differently in pesticides.
> In 67 day half will be gone, after 67 more days half of what was left is gone, so there is still a quarter of it left. After another 67 days you would still have an 1/8 of it still left. Its sort of like continually cutting a number in half. You never actually get to zero, except when you are talking about chemicals there is a last molecule that eventual breaks down.


You are correct in your thinking there, Phil. Half life is how long it takes for the amount to reduce to half. Every 67 days, the remaining amount is reduced by half. 

-Matt


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## Ed (Sep 19, 2004)

Half life is not the correct term when dealing with pesticides as noted by a couple of people. The correct terminology is persistence. 

Ed


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## McBobs (Apr 26, 2007)

Ed said:


> Half life is not the correct term when dealing with pesticides as noted by a couple of people. The correct terminology is persistence.
> 
> Ed


Ed. I love you and your all knowing. Don't ever leave us stranded to fend for ourselves here at DB.

<3

-Matt


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## earthfrog (May 18, 2008)

phender said:


> That is not what I understand half-life to mean, unless it is used differently in pesticides.
> In 67 day half will be gone, after 67 more days half of what was left is gone, so there is still a quarter of it left. After another 67 days you would still have an 1/8 of it still left. Its sort of like continually cutting a number in half. You never actually get to zero, except when you are talking about chemicals there is a last molecule that eventual breaks down.


So, the rate of breakdown would be represented like this (with the amount remaining in parentheses), correct?

At 95 days, (1/2 of compound remains) + 95 (1/4) + 95 (1/8) + 95 (1/16) + 95 (1/32) + 95 (1/64) + 95 (1/128), et cetera, et cetera...

So I guess I want to know---what is considered to be a negligible amount left, or a relatively benign amount left? How do we measure persistence, just in the amount of days it takes the pesticide to break down, or in the concentration of the pesticide, or both?


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## earthfrog (May 18, 2008)

earthfrog said:


> So, the rate of breakdown would be represented like this (with the amount remaining in parentheses), correct?
> 
> At 95 days, (1/2 of compound remains) + 95 (1/4) + 95 (1/8) + 95 (1/16) + 95 (1/32) + 95 (1/64) + 95 (1/128), et cetera, et cetera...
> 
> So I guess I want to know---what is considered to be a negligible amount left, or a relatively benign amount left? How do we measure persistence, just in the amount of days it takes the pesticide to break down, or in the concentration of the pesticide, or both?


....anyone?


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## edwardsatc (Feb 17, 2004)

Half life doesn’t really tell us much unless we know how compounds compartmentalize. In other words, how does the compound of interest partition to environmental compartments (air, water, soil, sediment). So when looking at the half life of a compound, one should also determine the environmental compartments in which it primarily resides. For example, you need to know how much a compound partitions to the soil before a half life is of much use in determining what the concentration of a compound may be after a certain number of hours/days. 

Half life is dependant upon many factors such as partitioning coefficients (Kd, Koc, Kow, …), organic matter content (of soil, sediment and water), solubility, vapor pressure, and temperature. So, half lives will vary widely in the literature. Additionally when discussing half lives, one should also discuss the parameters under which they were determined. For example, a half life of xxx at a temperature of 10 C, doesn’t mean much if the environmental temperature of interest is 25 C.

EPA EPIsuite can be used to model compound half lives and EPA EQC is a fugacity based model that can be used to model chemical fate and partitioning in the environment. Both are freely available for download on the EPA website.

I’ll run the models for bifenthrin and post the results here.

More later … I just got back from four days in the backcountry of Big Bend NP and a little exhausted.


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## edwardsatc (Feb 17, 2004)

Ed said:


> Half life is not the correct term when dealing with pesticides as noted by a couple of people. The correct terminology is persistence.
> 
> Ed


Ed, 
In terms of environmental persistence and fate, half life is the proper terminology as used in toxicology, analytical toxicology and chemical fate modeling. Half life is a measure or means of quantifying persistence. It is widely used in the toxicological, environmental fate, and analytical literature.


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## edwardsatc (Feb 17, 2004)

Here's a level III model I ran for bifenthrin using some very basic environmental parameters:


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## edwardsatc (Feb 17, 2004)

I did some basic modeling of bifenthrin. I haven't yet compared to experimentally derived values. Below is a small portion of the output (original output is 38 pages) for compound half live. Note the dramatic difference in stream vs. lake half life - this emphasizes the point that half lives are highly dependent on the specific environmental conditions of interest and that one must pay specific attention to environmental parameters when reviewing half lives published in the literature.










Basically the same information can be obtained from several chemical databases which use the same software to predict chemical properties and fate.


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## edwardsatc (Feb 17, 2004)

earthfrog said:


> So I guess I want to know---what is considered to be a negligible amount left, or a relatively benign amount left?


This is basically a risk assessment question. What is the target organism? What are the published toxicity levels? What is the exposure to the organism? Does the compound partition to a compartment where the organism is likely to be exposed?

The answer ultimately rests upon how much risk you deem acceptable. There are a variety of ways to calculate this based upon exposure, toxicity, and risk level. Software freely available to determine exposure includes TRex, T-Herps, KABAM, PRZM, EXAMS, .... and many others. If anyone is interested, feel free to contact me.


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## edwardsatc (Feb 17, 2004)

Chirality also plays a role in degradation of Bifenthrin (and many other stereoisomeric compounds). The stereoisomers of bifenthrin have been shown degrade at different rates. Note that in a racemic formulation, the ratio of R-cis and S-cis bifenthrin is 1:1 

Sujie Qin,, Robert Budd,, Svetlana Bondarenko,, Weiping Liu, and, Jianying Gan (2006)Enantioselective Degradation and Chiral Stability of Pyrethroids in Soil and Sediment Journal of Agricultural and Food Chemistry 54 (14), 5040-5045 http://pubs.acs.org.lib-e2.lib.ttu.edu/doi/full/10.1021/jf060329p


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## Ed (Sep 19, 2004)

edwardsatc said:


> Ed,
> In terms of environmental persistence and fate, half life is the proper terminology as used in toxicology, analytical toxicology and chemical fate modeling. Half life is a measure or means of quantifying persistence. It is widely used in the toxicological, environmental fate, and analytical literature.


 
I stand corrected.. All I can say in my defence is that when I do literature searches on these chemicals, I get a better response if I use persistence as opposed to half life. 

Ed


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## edwardsatc (Feb 17, 2004)

Ed said:


> I stand corrected.. All I can say in my defence is that when I do literature searches on these chemicals, I get a better response if I use persistence as opposed to half life.
> 
> Ed


Actually, I should clarify .... While there are no hard and fast rules, persistence is usually used with empirical data, while half life is typically a term used when modeling.


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## earthfrog (May 18, 2008)

edwardsatc said:


> Chirality also plays a role in degradation of Bifenthrin (and many other stereoisomeric compounds). The stereoisomers of bifenthrin have been shown degrade at different rates. Note that in a racemic formulation, the ratio of R-cis and S-cis bifenthrin is 1:1
> 
> Sujie Qin,, Robert Budd,, Svetlana Bondarenko,, Weiping Liu, and, Jianying Gan (2006)Enantioselective Degradation and Chiral Stability of Pyrethroids in Soil and Sediment Journal of Agricultural and Food Chemistry 54 (14), 5040-5045 http://pubs.acs.org.lib-e2.lib.ttu.edu/doi/full/10.1021/jf060329p


Ok---I could not access the study you posted without a special code---but just for the sake of sorting this out---
Is the issue of chirality, or assymetrical nature of the compound, significant because it is reactive to itself and other organic compounds? 

Or is the primary issue that it also optically active? Is this more significant than its formerly-listed causes of degradation? 
What are the most significant prevailing environmental variables that contribute to this degradation in regards to the chirality of its molecular structure? (this is probably listed in the study, but I can't access it, sorry).


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## earthfrog (May 18, 2008)

edwardsatc said:


> This is basically a risk assessment question. What is the target organism?


For starters, isopods. 



> What are the published toxicity levels?


I am not sure I could find this. I would need help with this one. It would depend on the route of exposure, but I am assuming ingestion would be the main concern.



> What is the exposure to the organism?


ingestion of contaminated plant matter.



> Does the compound partition to a compartment where the organism is likely to be exposed?


What I would ask in this regard is, does this compound, bifenthrin, actually bond to the molecules of the plants which the isopods may consume? 
This (Bifenthrin) document suggest that it is not absorbed by the plant, nor is it translocated in the plant, but I don't think that answers the question (assuming my layman's derivative of your question is correct). 




> The answer ultimately rests upon how much risk you deem acceptable. There are a variety of ways to calculate this based upon exposure, toxicity, and risk level. Software freely available to determine exposure includes TRex, T-Herps, KABAM, PRZM, EXAMS, .... and many others. If anyone is interested, feel free to contact me.


Yes, I would like help in order to begin calculating the toxicity of each of these compounds, one at a time, and ruling out certain variables---for one, it is relatively stable in light and at lower temps, so heat and chirality could be considered more closely, I guess. (I'm not a chemist, so I am probably talking balderdash, but I'm sure you'll correct that if so.) I think posting that here on this thread would clear the air considerably for a lot of folks.


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## earthfrog (May 18, 2008)

Any chemist want to tackle the last post I made here, just above this one? 

BUMP*


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