hi everyone welcome back to public health 462. this is second part of topic six toxic effects of pesticides and pesticide residues in the first part we discuss the different examples of herbicides rodenticides and fungicides now we are going to talk about insecticides insecticides are type of pesticides that are designed to kill insects insects cost about 4 billion dollars lost annually and there are many different species of insects that eat our crops as well as the fact that some of these insects can cause vector-borne diseases use of insecticides have decreased over time and one of the reasons for that is because insecticides have become much more toxic and they are much more specific and there's also this idea behind that organic fruits and vegetables are safer so you have organic farmers that are voluntarily intentionally not using pesticides including insecticides and we have been using genetically modified organisms thapyruvsinnately produce insecticides in its tissue i'm going to talk about three different classes of insecticides organochlorine is one of them pyrathroids is another i'm going to group organophosphates and carbomides together because their mechanism of toxicity are very similar organophosphates and carbamides target an enzyme in the nervous system and this enzyme is called acetylcholine esterase it is a enzyme that breaks down a neurotransmitter called acetylcholine so organophosphates and carbamides inhibit this particular enzyme and i'll talk about the mechanism more in detail pyrethroids and organochlorines an example of organochlorine is ddt pyrethroids and organochlorines like ddt activate the sodium channels they by activating the sodium channel it disrupts the nervous system process and this causes spasm and spasm leads to death i have a lot of videos i think it will be useful for you guys to watch these videos it will be very beneficial so i'm going to group these insecticides into the target site here we have pyrethroids and organochlorines like ddt target the sodium channel and they activate the sodium channel later we'll talk about how organophosphates and carbonates inhibit acetylcholine esterase organochlorines and pyrithroids insecticides open up sodium ion channels in neurons this causes this influx of sodium ions into the nerve cells and it fires very quickly and there's too much information that causes the nervous system to actually break down so before we understand how organochlorines and pyrithroids cause toxicity in insects we have to understand a little bit about action potential and how the nervous system works here's one cell of a nerve uh it actually has the dendrites these are the dendrites here's the axon and here are what we call presynaptic terminal or synapse so the way the your body is able to move the information down your nervous system is using electrical current and the way they do it is if you look at the exon of a nervous system you'll find the outside is actually more positive and that's because there are more sodium ions in the outside so there it makes the outside a little bit more positive inside the nerve cell there are more potassium ions so when you actually have a receptor that starts the process of sending information it opens up the sodium channels because when the sodium channel opens up because there's more sodium outside than inside sodium flows in this makes inside the cell more positive when there's this positive potential inside the nerve cell it activates the adjacent sodium channels so the adjacent sodium channels open up and that will allow sodium ions and again the adjacent one will open up as well and this allows sodium ions so what ends up happening is this sort of positive charge that was started will flow down the exon in one direction so this positive ion or positive charge is moving along the exon okay so that's how information is moved within the body and how does it go back to its original charge state well once there is positive charge inside the cell you also have these potassium channels that open up when the potassium channels open up because there's more potassium inside than outside potassium will leave and basically positive ions leave the nerve cell and that will bring back the charge state back to its resting state pyrethroid is a synthetic chemical compound that's similar to the natural pyrethrin so pyrethrin is derived from the nature it's derived by a flower called pyruvs and from that we've extracted this chemical that is able to kill insects and using that chemical structure we've modified them and this modification is what we call pyrethroids it's a synthetic chemical one good thing about pyrethrins and pyrithroids is that they tend to break down quite readily in the presence of sunlight so it is much safer to use later we'll learn that typical home insecticides like raid will contain pyrethroids and as mentioned earlier the way the pyrethroids work is it keeps that sodium channels open it doesn't close if it doesn't close sodium ions will continue to enter in so here's another picture if sodium ion continues to enter it will cause continual stimulation right that sodium channel is supposed to close as soon as uh sodium ions enter and cause this action potential pyrithroids bind to the sodium channel and prevents it from closing normally this results in a continuous nerve stimulation and this can lead to tremors and uncoordinated movement and it will lead to spasm and if it's a human person who is exposed to high levels of pyrethroids it will cause spasm in the respiratory system and the person would not be able to breathe and will die as a result of suffocation the dermal toxicity of pyrethroids is relatively low and once pyrotheroids are absorbed in humans they tend to metabolize very quickly and the half-life of permethrin for example is only about a day so these insecticides do not have very long half-lives shorter half-life usually means that it's safer here is the structure of pyrethrin and here is a structure of permethrin so you can see some similarities here right between the two all right there's some similarity pyrethrin is from the flower itself we've extracted the chemical and using this as a model we have built different pyrethroids so here is the active ingredient that you'll find in a bottle of raid and it uses permethrin as the active ingredient to kill insects the acute and oral mammalian toxicity of pyrethroids are generally low that's why it's used in the home setting values of ld50 range for example from 100 milligrams per kilogram for delta methylene to about 10 000 milligrams per kilogram for phenothrin the low mammalian toxicity of pyruvates is confirmed by the fact that despite their extensive worldwide use there's really relatively few reports of human poisoning and we continue to use these type of insecticides for home use and there's very low chronic toxicity as a result of exposure to pyrethroids pyrithrin tends to be safer compared to pyrithroids synthetic pyrethroids compounds vary greatly in its toxicity depending on what was added however as a whole class of chemicals pyrethrus tends to be safer than other insecticides if you do inhale high levels of pyrethrum it can cause asthmatic breathing sneezing nasal stuffiness headache nausea in coronation at high levels of exposure it starts to impact the nervous system because just like in insects pyrethroids can disrupt the nervous system in humans now let's talk about organochlorines organochlorines are derived from chlorinated hydrocarbons which are chemical compounds that contain chlorine carbon and hydrogen as we have learned this chlorine to carbon bond tends to be very lipophilic it's characteristically very stable and also very fat soluble and because it is fat soluble it is very persistent it tends to stay in the environment for a long time and because it stays in the environment for a long time because they are persistent they tend to travel long distances and some of these organochlorine chemicals are associated with damage to the immune system as well as cancer so here are some examples of organochlorine pesticides they include ddt lindane chlordane aldrin dialdron andron and hexachlorobenzene all of these chemicals are banned as an insecticide because now we know that these organochlorine pesticides are very very toxic many of these can actually cause cancer and the fact is they are very persistent they don't really break down very quickly in the environment and they tend to bio accumulate if you look at the structures of these organochlorines you find that yes you see a lot of chlorines that's bound to carbon and that's the similarity all of these as you can see are very very lipophilic now i'm going to briefly talk about ddt ddt is a very controversial topic one because ddt is persistent although ddt has been banned here in the united states in 1970s they're still in the environment because they're so persistent and the metabolites of ddt and the ddt themselves can perhaps cause endocrine disruption in animals and in humans so it's been a concern at the same time ddt really was used to fight malaria so here's incidence of malaria before and after the use of ddt in cuba before there are 3 500 cases after ddtus there are only three cases jamaica 4 417 cases then zero cases in venezuela there were eight million cases before the use of ddt and after many years of use there are only 800 cases india there were greater than 100 million cases of malaria before the use of ddt and after many years of use it dropped down to about 290 000 cases in yugoslavia about 169 000 cases after ddtu's about 15 taiwan greater than 1 million cases after ddtus and 0 you can just see how many people were saved as a result of ddtus so ddt really did save a lot of people but at the same time you know a lot of people are exposed to ddt and the consequences of the exposure is probably unknown at this point so the most important exposure route of ddt is the oral exposure that's because ddt tends to bioaccumulate in the environment but they can also be absorbed through inhalation and dermal exposure and for many years ddt was made into a sprayable form where you can spray it in a home to kill insects and this could lead to inhalation exposure and once ddt is absorbed it does break down it does go through biotransformation but the initial biotransform metabolites are still going to be very lipophilic and they tend to be stored in adipose tissue so for example if i were to get a sample of my adipose tissue and analyze for ddt there's probably going to be some ddt or the metabolites of ddt even though ddt really hasn't been used here in this united states since 1970s after it was banned so in humans ddt is extensively but slowly metabolized into two primary metabolites dde and ddd really there isn't a huge difference between the metabolites and the parent chemical and all of these are still very lipophilic and exposure to these metabolites are concerned because they are considered to be endocrine disruptors ddt is currently only produced in three countries india china and north korea india is far the largest producer of ddt and they are the largest consumer of ddt in 2005. in 2005 the primary use of ddt although it is banned in most developed countries it was used to fight malaria and control malaria the reason why ddt is very good at reducing malaria infection is because it is very persistent you can spray inside your house let's say every six months or maybe every year and because ddt is very persistent it lingers around inside the house to prevent insects from coming in you probably heard of mosquitoes that are resistant to ddt so some mosquitoes no longer die as a result of exposure to ddt but ddt still works as a repellent it doesn't kill them but they still don't like it ddt is moderately to slightly toxic to study mammalian species via oral roots reported oral ld50 is from about 113 to about 800 milligrams per kilogram in rats what's interesting about ddt is that for many years ddt was used in many different kinds of wars like the world war ii many military personnel has been exposed to ddt in fact in the old days there's still documents available that shows military personnel being exposed to intentionally being exposed to ddt to just see the toxicity it is a very well studied chemical so in human exposure studies have been conducted in many different occasions via oral dermal and respiratory pathways and there has been a lot of studies on ddt so one of the correlations that we find between ddt exposure and human health is that it may lead to increased spontaneous abortion lower sperm quality and even breast and pancreatic cancers that are weakly associated here's an interesting article about ddt here's a video that you should watch about zika zika and malaria are different kinds of infections but the idea is that they're both vector-borne diseases and it's something that we all as society are going to have to face and fight now let's talk about the other class of insecticides these are carbamides and organophosphates and i really group them together because their mechanism of toxicity are very very similar they inhibit the enzyme called acetylcholine esterase in order for me to explain how organophosphates and carbonates work we need to understand a little bit about the synapse between two nerve cells so synapse is this intracellular junction the point of communication between two neurons we don't have one big neuron that spans across all the way from your brain to the tip of your toes they're connected by many different neurons we already learned how information travels inside the nerve cell through exon and this related to once again the sodium channels and potassium channels sodium channels open up and sodium ions enter and causes this action potential and then potassium channel opens up and that brings it back to the resting state so we know how information travels within a cell now we need to learn how this information travels between two cells this is through an area called synaptic terminal it is the area between the presynaptic and postsynaptic terminals presynaptic terminal usually is on the tip of the axon which sends the information postsynaptic terminal is the one on the dendrite of the nerve cell that's receiving the information the one who receives is postsynaptic terminal one who sends is presynaptic terminal so this is how acetylcholine neurotransmitter work information moves along the exon as sodium channels and potassium channels open up by the time this information this positive charge comes near the presynaptic terminal you cannot move that electrical charge across this empty space so when this information arrives at the pre-synaptic terminal it initiates a process in which vesicles that contain these neurotransmitters these are information chemicals are then released into the synaptic cleft and then they bind to the receptor which starts this process of opening up sodium channels and will cause action potential and that that positive charge can move along the axon of the new nerve cell once that acetylcholine is used to stimulate a response in the postsynaptic terminal it can't stay there forever because it can't continue to stimulate so once the neurotransmitter acetylcholine leaves the receptor then it is bound by a an enzyme called acetylcholine esterase and the job of the acetylcholine estera is to break that acetylcholine neurotransmitter into two components choline and an acidic acid and they are no longer active as neurotransmitters and they are shuttled back into the presynaptic terminal so that they can be put together back into acetylcholine and they'll be put into a vesicle to be ready for next signal some acetylcholine just kind of leaves the cleft area and then eventually they get destroyed not all of them gets pulled back into the pre-synthetic terminal so here's just a picture that shows information this is this positive charge that moves along towards a presynaptic terminal and here are these vesicles once this positive charge initiates a process of making these vesicles fuse into the presynaptic terminal once the vesicles fuse it opens them up acetylcholine neurotransmitters are released into the synaptic cleft and eventually they bind to the receptor they start a signal and that signal the positive charge that moves along the axon of the new nerve cell and these acetylcholine neurotransmitters are then put back well before they do that they have to be broken down by the enzyme they're broken down by enzyme and their shuttle back into the presynaptic terminal watch this video that kind of explains how the acetylcholine works so both carbamides and organophosphate insecticides bind to the enzyme called acetylcholine esterase it is an inhibition process it prevents the enzyme from doing its function so the enzyme is designed to stop the nerve impulse because it breaks down the neurotransmitter however when organophosphates and carbamides bind to the enzyme as acetylcholine esterase enzyme the enzyme itself stops breaking down the acetylcholine into its components therefore they're still lingering acetylcholine neurotransmitter in the cleft continuing to stimulate the postsynaptic terminal and this allows this continual stimulation continuing to fire and sending more information to the postsynaptic terminal even though there is no innervation in these nerve cells so organophosphates and carbamides inhibit acetylcholine esterase in order to understand how this works let's see the normal functioning of acetylcholine esterase when it's bound to acetylcholine acetylcholine esterase is a big enzyme it's just here it's showing the two active sites where the acetylcholine will bind so acetylcholine needs to have the right structure right physical structure to be able to fit into these active sites well acetylcholine does because acetylcholine is the correct substrate for this enzyme so when acetylcholine binds to acetylcholinesterase it will break that acetylcholine into acidic acid and chlorine and this is the normal functioning of acetylcholine esterase now instead of acetylcholine if for example organophosphate or carbamide binds to this active site of the acetylcholine esterase because of similarity in its structure it will bind to the active site and it will stay there if this stays there acetylcholine will not be able to bond and if it cannot bond to the active site acetylcholine stay as the active form it will continue to stimulate and innervate the postsynaptic terminal and what ends up happening is that this organophosphate will stay either the organophosphate or the carbon mint will stay there for long periods of time if it's a permanent bonding this enzyme becomes useless and it will need to be broken down and new enzyme will need to be made again there are two pathways in which these insecticides can take as mentioned if it's acetylcholine that's binding to the active site of the acetylcholine esterase eventually the acetylcholine is broken down and then it regenerates the acetylcholine x-ray so it can grab another acetylcholine instead of acetylcholine if you have organophosphate or carbamide that binds to the active side and this becomes sort of an almost very strong bond and at this point it can take two pathways one pathway eventually will allow the organophosphate or the carbamide to leave and regenerate acetylcholine esterase in another pathway this complex goes through aging process in which this complex becomes so stable it will stay there forever and this enzyme is no longer usable so this table defines some differences between organophosphates and carpets organophosphates tend to be more toxic then carbamides carbons are usually less toxic than organophosphates organophosphates are higher in toxicity and the duration is also longer because the complex when the organophosphate binds to the enzyme it tends to be more of a permanent bond so that duration of action is longer and the toxicity is usually more common than carbamides these are the cholinergic effects when a person is exposed to either organophosphates and carbonates we can use the acronym dumbbells to describe these effects a person has diarrhea urination meiosis bradycardia emesis lacrimation and salivation all of these are related to toxicity to the nervous system for all organophosphates that contain sulfur atom and the sulfur atom is bound to the phosphorus that sulfur needs to be metabolized and will need to turn into oxygen in order to become activated it needs to turn into that phosphorus bond to oxygen because once the activated organophosphate binds to the acetylcholine estrogens that complex tends to be much more irreversible compared to carbamides here's an example melothion this is the inactive form that needs to be changed into oxygen to become activated melodyne is slightly toxic via oral roots with report oral ld50 values about thousand milligrams per kilogram it is also slightly toxic via dermal root and human volunteers were fed very low doses of melathion for about one and a half months showed no significant effects on blood clean esterase activity well one of the reasons is that once you absorb melation this needs to be metabolized and be activated that needs to turn into oxygen so it tends to be a little bit less toxic compared to some of the other organophosphates melatine is rapidly and effectively absorbed by practically all roots including gi tract skin mucous membrane and lungs and the half-life is approximately eight hours in rats and about two days in cows and it needs to be activated the treatment for organophosphate poisoning is atropine and atropine is used in the military as well because some of the chemical weapons that's produced in the past are very similar to organophosphates if you have watched the movie the rock it's about a group of military personnel who is unhappy with the government and threatens to fire vx gas to san francisco as you can see this vx gas is similar in structure as organophosphate where you have the phosphorus bound to that oxygen vx gas or these chemical warfare are designed to kill humans right just as organophosphates are designed to kill insects it really has similar toxic effects and to block the action of vx gas atropine needs to be injected carbon insecticides are derived from carbonic acid and like i said carbonate tends to be less toxic than organophosphates it reversibly binds to acetylcholine esterase meaning that that complex is not permanent it tends to come off and regenerate the active site in the acetylcholinesterase an example of a carbon mint is carbaryl or seven seven is the trademark name direct contact of the skin or eyes with moderate levels of this pesticide can cause burns the oral ld50 of carbaryl ranges from about 20 50 milligrams to about 850 milligrams per kilogram in rats most animals including humans readily break down carbaryl and rapidly excrete it in the urine one of the environmental tragedies that have happened in 1984 is the release of chemicals that were used to make her barrel and it happened in papua india the union car by india limited factory was built in 1969 to produce the pesticide 7 as we mentioned using this chemical called methyl isocyanate and in 1984 there was a explosion that released this methyl isocyanate and other intermediate chemicals that have caused a lot of people to die as well as causing blindness to many people so this just kind of gives you the summary of different ld50s that we have discussed in this lecture now let's talk about a few pesticide policy i'm not going to spend a lot of time here there are three concerns involved in pesticide regulation that pesticides must be evaluated for intended use and impacts on human health must be described and users of pesticides must be trained and be able to protect themselves from the exposure and the public must be also protected from the risk of pesticide residues so the last topic that we're going to talk about is pesticide residue one of the first important law regulating pesticides is called the federal insecticide fungicide and rodenticide act known as fifra fifra empower epa to have jurisdiction over the manufacturing process use sale and testing of all pesticides and if the epa determines that the pesticide causes unreasonable adverse effects on the environment or in among humans this pesticide can either be restricted or banned there are three agencies in the united states that are involved in protecting consumers from pesticides on food epa they set the allowable tolerance for residues that's found in the food fda monitors and enforces the tolerance levels on most foods and food safety inspection service through usda monitors and enforces tolerance on meat poultry and eggs in 1938 the delaney clause of the federal food drug and cosmetic act was passed which did not allow any detectable residues of pesticides on food if it presents any risk to cancer now in 1996 new law was passed called food quality protection act so this is one of the more recent law regarding pesticide use one of the important things that he did was to eliminate the delaney clause that's because as our technology improves we are finding that there are always small amount of pesticide residues that can potentially cause cancer and if the concentration is really small what epa is basically saying is that even though some of these pesticide residues may pose a increased risk for cancer if the concentration is really really really small and our technology has improved so much that we can detect very small amount we should allow them to be in the food otherwise a lot of the food that we have can no longer be consumed by humans in addition to that the food quality protection act added new safety standards including having special consideration for children exposed to residues prohibition of pesticides that carry a risk of cancer more than one in a million so if it's less than one in a million this law allows the pesticide residues to remain in the food hence the elimination of the delaney clause and all products over 10 years must be reassessed and re-evaluated and the raw and processed foods have the same standards so this law really was designed to protect children because now epa will add 10 fold safety factor in addition to all the assumptions that we talked about for children that's because children eat more fruits and vegetables per unit of body weight they are much more susceptible to these carcinogens because of their smaller body weight and larger consumption of fruits and vegetables tolerances that's set by epa is the amount of pesticide that can remain in or on foods for human consumption for example melatonin tolerance on crops is about eight parts per million but in milk because milk is usually consumed by children it has to be much much lower about 0.5 parts per million usda monitors pesticide and pesticide residues through this pesticide data program so pdp data are used primarily by so pdp data are used primarily by epa to prepare realistic pesticide dietary exposure in people pdp provides high quality data residues in food that are more likely to be consumed by infants and children pesticides and commodities included each year's pdp are selected based on epa's data needs so in 2014 these were the states that were involved in the pdp data apples contain 18 different pesticides as pesticide residues so in this data these pesticides are analyzed and the percent of detections were found for each pesticide there were 177 samples and each sample were tested for 18 different pesticides it also gives you the number of samples with detections and the range of detections and the means of detections so this is a mean of all the detected 18 pesos side residues that was detected on and inside the apple and here is the epa tolerance level as you can see all of the detection concentrations were below the tolerance level same thing with peaches it shows you the detection level here is the average detection of these different pesticides and here's the epa tolerance level i love peaches and it's hard to grow peaches without any pesticides but i'm willing to eat a little bit of pesticides because i really love peaches and the idea is that the detection level is much less than the tolerance level set by epa and if you trust epa not that all of us or not that i always trust epa but hopefully there are good scientists there and if they're right the exposure that i have by eating peaches should be should increase the toxicity very very little almost zero and that's what i'm hoping even watermelon will have different kinds of pesticides there are six pesticides that were found and their levels once again are much much smaller than the tolerance level so they also looked at the number of different kinds of pesticides that were detected per sample about 41.5 percent of the samples has zero pesticides which is great right this is not organically grown but 41.5 percent of all the samples that were detected had zero pesticides about 15 percent had one pesticide about 12.7 percent had two pesticides about 8.7 at three different pesticides so there are few that have 17 different pesticides so you can see this data apples about 4.5 of the tested has zero pesticides and about 23.7 percent of apples that were tested had four different kinds of pesticides carrots about 38.3 percent had zero pesticides sweet corn 98.5 percent had zero pesticide summer squash about 50.7 percent has zero pesticides watermelon more than half of the watermelon tested has zero pesticides they also test for processed fruits and vegetables sweet corn frozen very low very interesting data right so in 2014 over 41 percent of the samples tested had no detectable pesticide residue similar to eating organic fruits and vegetables and over 99 of the samples tested had residues below the tolerance established by the epa so if you do once again believe the epa that even though some of these crops are grown traditionally using pesticides 99 of them are below the epa's established tolerance level residues exceeding the tolerance level were detected in 0.36 of the samples and of these 38 samples 19 of them were important so it's much more likely that if you were to eat imported fruits and vegetables that they would have more pesticides here in the united states compared to most developed countries we do have more strict pesticide laws eu actually have more strict laws compared to the united states residues with no established tolerance were found in 2.6 of the total sample tested all right that's about it i know this is relatively long lecture but please do spend time going over some of the important concepts that i discuss in this lecture read the require reading and also re-watch the video if you have to all right take care