So instead of jumping into the manufacturing of plastics, I will pick up on a piece that wasn't adequately addressed in my last post. I always think about the dangers of sensationalizing associations;
there is a lot of stress and worry over unsubstantiated claims out
there! My hope is for this blog to generate a fair and critical
discussion about thoughts and concerns over plastics. However, I fear I was too dismissive of
evidence of phthalate (a component of plastics and fragrances) exposure and asthma or autism. After writing that I had never heard of such association, it was a topic of discussion in one of my classes the very next day! I thought this would be a very relevant post because so many of us are affected by asthma and autism, either directly, or through people that we know. So without getting too caught up in the biology of this, I'll try to explain how these associations exist.
To start talking about asthma, we first need to briefly put it in the context of allergies. Allergies are basically an over-reaction to harmless substances by our immune system. The immune system is our body's defense for any kind of foreign substances, such as viruses or bacterias, and the way we are able to fight off harmful substances (like the influenza virus) is through the work of T and B cells in our immune system. These cells produce antibodies, which are formed to recognize antigens, or outside substances. An over-production of antibodies can lead to allergic responses, such as hives, swelling, or asthma. Asthma is an allergy that occurs specifically in the lung. So where do plastics play a role here? Well, some chemicals can act in a way that enhances the immune response. "Enhances" is emphasized because it means that such a chemical alone can't stimulate an immune response by itself (although some chemicals can), but it can contribute to an inappropriate immune response. Because phthalates cannot bind to proteins, they may serve as an enhancer to this allergic process. This has been examined experimentally, and in one study, phthalates were administered along with ovalbumin (main protein found in egg whites) to mice.* The production of ovalbumin-specific antibodies was significantly increased when ovalbumin and pthalates were administered together, as opposed to a much smaller antibody response when ovalbumin was given alone. This is interesting because, as I mentioned earlier, the over-production of antibodies is what leads to an allergic response! But now I will get back to my point above about being careful about associations, because there are some very important pieces to this study that I didn't tell you. The enhancement of antibodies was seen at the lower doses phthalates, meaning less antibody production occurred at the high doses of phthalate administration...think about this. So, the amount of chemical exposure is very important, (and, no, from looking at this study, it can't be determined what that dose is for humans). Also, this study was done on mice (we are not mice), and the phthalate and egg white protein was injected under the skin. How often do you get injections of plastic right into your body? However, another study in which phthalates were inhaled by mice, which is a more reasonable exposure in regards to asthma, similar trends were seen. Observations in humans show that people who are occupationally exposed to phthalates have higher rates of asthma, which is why this connection is so compelling to study experimentally. Also, asthma and allergy rates have been increasing at remarkably similar rates since the 1960s. I felt the need to delve into this because 1. I had never heard of this before! and 2. I love to consider all the realms of possibilities of our bodies interactions with plastic.
Autism is a disorder that has received a lot of attention lately because the number of cases has increased dramatically in the past two decades. I wish I could give a similar introduction to the cause of autism like I did for allergies, but its cause is still unknown. There are many theories about why we are experiencing this increase (the vaccine theory has been proven bogus), but scientists are searching for answers for its cause and increased incidence. An association between autism and phthalate exposure was observed from a study in which pregnant mother's phthalate exposure was measured, and subsequently their children's behavior was followed when they reached age 7 to 9. The children who had the highest in-utero exposure to phthalates (as measured from their mom's exposure during pregnancy), scored significantly poorer on social cognition, social communication, and social awareness than those who had the lowest in-utero phthalate exposure. These results were scaled to the Autistic Spectrum Disorder scale used for the general population. The hypothesis that there is a developmental component to autism is becoming more widely acknowledged in the current scientific arena. Additionally, the environment is considered to play a large role in autism because genetics (or twins) explain just one-fourth of autism cases. While this association isn't as biologically satisfying because there are so many uncontrolled factors (like, what else were the moms exposed to?), it is certainly worth more studies and observations. I look forward to following these studies and telling you how we're coming along on solving this mystery.
*I am an animal lover, and while it makes me sad to think about animals being used in experiments, there is not yet an adequate model for studying chemical effects without them. Humans can't be used because it would be unethical to possibly make someone sick. The Environmental Protection Agency has been working on a computer model called ToxCast that uses computer modeling to make predictions about chemical behavior in the human body, and it is currently being validated for some new chemicals. It will be a huge animal, time, and money-saver when computer models can be used for toxicological experiments!
To start talking about asthma, we first need to briefly put it in the context of allergies. Allergies are basically an over-reaction to harmless substances by our immune system. The immune system is our body's defense for any kind of foreign substances, such as viruses or bacterias, and the way we are able to fight off harmful substances (like the influenza virus) is through the work of T and B cells in our immune system. These cells produce antibodies, which are formed to recognize antigens, or outside substances. An over-production of antibodies can lead to allergic responses, such as hives, swelling, or asthma. Asthma is an allergy that occurs specifically in the lung. So where do plastics play a role here? Well, some chemicals can act in a way that enhances the immune response. "Enhances" is emphasized because it means that such a chemical alone can't stimulate an immune response by itself (although some chemicals can), but it can contribute to an inappropriate immune response. Because phthalates cannot bind to proteins, they may serve as an enhancer to this allergic process. This has been examined experimentally, and in one study, phthalates were administered along with ovalbumin (main protein found in egg whites) to mice.* The production of ovalbumin-specific antibodies was significantly increased when ovalbumin and pthalates were administered together, as opposed to a much smaller antibody response when ovalbumin was given alone. This is interesting because, as I mentioned earlier, the over-production of antibodies is what leads to an allergic response! But now I will get back to my point above about being careful about associations, because there are some very important pieces to this study that I didn't tell you. The enhancement of antibodies was seen at the lower doses phthalates, meaning less antibody production occurred at the high doses of phthalate administration...think about this. So, the amount of chemical exposure is very important, (and, no, from looking at this study, it can't be determined what that dose is for humans). Also, this study was done on mice (we are not mice), and the phthalate and egg white protein was injected under the skin. How often do you get injections of plastic right into your body? However, another study in which phthalates were inhaled by mice, which is a more reasonable exposure in regards to asthma, similar trends were seen. Observations in humans show that people who are occupationally exposed to phthalates have higher rates of asthma, which is why this connection is so compelling to study experimentally. Also, asthma and allergy rates have been increasing at remarkably similar rates since the 1960s. I felt the need to delve into this because 1. I had never heard of this before! and 2. I love to consider all the realms of possibilities of our bodies interactions with plastic.
Autism is a disorder that has received a lot of attention lately because the number of cases has increased dramatically in the past two decades. I wish I could give a similar introduction to the cause of autism like I did for allergies, but its cause is still unknown. There are many theories about why we are experiencing this increase (the vaccine theory has been proven bogus), but scientists are searching for answers for its cause and increased incidence. An association between autism and phthalate exposure was observed from a study in which pregnant mother's phthalate exposure was measured, and subsequently their children's behavior was followed when they reached age 7 to 9. The children who had the highest in-utero exposure to phthalates (as measured from their mom's exposure during pregnancy), scored significantly poorer on social cognition, social communication, and social awareness than those who had the lowest in-utero phthalate exposure. These results were scaled to the Autistic Spectrum Disorder scale used for the general population. The hypothesis that there is a developmental component to autism is becoming more widely acknowledged in the current scientific arena. Additionally, the environment is considered to play a large role in autism because genetics (or twins) explain just one-fourth of autism cases. While this association isn't as biologically satisfying because there are so many uncontrolled factors (like, what else were the moms exposed to?), it is certainly worth more studies and observations. I look forward to following these studies and telling you how we're coming along on solving this mystery.
*I am an animal lover, and while it makes me sad to think about animals being used in experiments, there is not yet an adequate model for studying chemical effects without them. Humans can't be used because it would be unethical to possibly make someone sick. The Environmental Protection Agency has been working on a computer model called ToxCast that uses computer modeling to make predictions about chemical behavior in the human body, and it is currently being validated for some new chemicals. It will be a huge animal, time, and money-saver when computer models can be used for toxicological experiments!
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