If you're ever asked to name a portion of the population that is both extremely vulnerable and susceptible to environmental hazards. And by the way, that would be a great exam question. The answer you should come up with first is children. Let's explore why. First, let's talk about what makes children vulnerable. And the first reason here that I'd like to highlight is poverty. So we know that people living in poverty tend to have higher exposures. Unfortunately, 13% of Americans live in poverty, but 20% or one in five children in the United States live in poverty. So poverty is associated with higher rates of exposure to toxic chemicals. Now, we know that poorer nutrition which we tend to find in people with lower income is all by itself harmful to health, but poor nutrition can also increase your internal dose of some toxicants. For example, if you have a diet that's deficient in calcium, your body is going to uptake more lead than if you have a diet that's rich in calcium, which actually protects you from absorption of lead. We also know that children in poverty tend to have fewer opportunities for recreation and education and also have decreased access to medical care. The second reason I'd like to focus on is biological characteristics and this would be defined more as susceptibility, which is a concept with invulnerability. We need to understand that pound for pound, children drink more water and they eat more food and they breathe more air in a given day than adults. We can think about specific differences for example, in infants. So infants drink 7 times as much water as adults, water being the major constituent of formula as well as breast milk. Infants also breathe 3 times faster than adults and breathe 2 times as much air per body weight compared to adults. Let's look into this a little bit more in terms of susceptibility. We know that children's bodies are developing. Their metabolic pathways are immature and they have different abilities to detoxify and excrete toxic chemicals than do adults. Unfortunately, their abilities are different and usually worse. We also know that in children each system, so their central nervous system, their liver, their cardiovascular systems, their immune systems, they develop at different rates. And so the periods of key development for each of those system also represent windows of special vulnerability. We know that chemical exposures during those windows of vulnerability can cause cell loss. It can alter the process of neurons connecting such that anatomically those neural connections can appear normal, but functionally, they don't work as well. It can also inappropriately turn on or off signals which regulate DNA transcription so that can lead to potentially catastrophic disease down the road. The third reason I'd like to highlight here are behavioral characteristics. So for example, children have unique food patterns. They drink 21 times more apple juice and 11 times more grape juice than adults as a sort of ridiculous example. Children love to put their hands in their mouths. That hand to mouth behavior begins almost immediately and doesn't dissipate until 3-4 years and children are low to the ground. Whatever's on the floor, if that's dust or soil or other materials, chances are it's going to get ingested. We also know that some toxic chemicals tend to sequester in lower lying areas of your home. So for example, pesticide vapors are going to be found down close to the floor where children are breathing. And some types of chemicals selectively accumulate on lower surfaces like carpet. Finally, children are exploratory. They literally get into everything. And if so if there is a potential exposure for them to have, eventually they're going to get into that exposure. We can ask and we do ask in environmental health questions like, what might be predictive of an individual child's blood lead level? So what environmental or behavioral attributes might predict a child as having a higher blood lead level than other children? And it turns out these blood lead levels depend on a variety of things in children. One is behavior, so again, eating soil, playing outside, this hand-to-mouth behavior. A second factor is biological differences in race and ethnicity. And a third relates to exposures, having things like paint lead or lead in your soil as well as income. Now the graphic we're looking at here on the right is showing you basically the relative contribution or importance of different factors about a child's environment or their behavior and relating those factors to their blood lead level. So let's start in the upper left-hand corner. The presence of paint in lead in a child's home actually is the most important predictor of them having a high blood lead level. So it's got the highest coefficient here of .414 but there are other attributes here. So the presence of soil in lead is another issue. Paint and soil that contain lead can both produce lead containing dust which can then be ingested by a child. Soil lead can either turn into dust or get onto the child's hand and then get consumed and increase blood lead. As you'll see on here, the second most important factor for a higher blood lead level is black race with a coefficient of .319. You can also see income here has a negative correlation. So the higher a family's income, the lower their child's blood lead level is going to be. And finally, we have factors like playing outside and eating soil. So among all these predictive factors, again, the most important two for predicting a child with a higher blood lead level are presence of lead in paint in the home and black race. Now we have to understand that children are not only exposed at home. We often think of them as spending a lot of time, but they have exposures that occur in many settings at a range of scales. So they may be at their home a relatively small spatial scale or in their general community or being exposed to their sort of regional ambient environment. For children, though uniquely most of the exposures occur at home. Now the WHO has created this graphic on the right here showing in circles a number of different exposures that children can have. So children are exposed to different social environments that can impact their health. They're exposed to different types of housing and shelter. They have outdoor and indoor air pollution exposure. They can be exposed to noise, to solid waste, and to the potential transportation and industrial accidents. Children can have a range of access to sanitation and hygiene. They can be exposed to hazardous chemicals. They can have differential water quality and supply. They can be exposed to disease-causing vectors, again, all of these things happening in their home or the community or in the ambient environment. They might live in an area where there's natural hazards, like earthquakes. They might have food security and food safety issues. Finally, the children might live right here in Michigan and have exposure to ionizing radiation through radon in their home. So children do have all of the same types of exposures that adults have but again, the key difference here is for children, most of these exposures are going to happen in the home. The WHO has also studied the 5 leading environmental causes of death among children around the globe. You can see those portrayed on the graph here. The 5 leading causes of death are perinatal disease, respiratory disease, diarrheal disease, vector-borne disease, and finally, physical injuries. So if we look at the graph, you can see those top 5 categories. You'll also see different colored bars associated with each. The blue is for the oldest category of children here, age 5 to 14. And then the olive colored bar is indicating the group between 0 and 1 years. So you can see for the top four leading causes of death here, the vast majority of the burden is happening among children age 0 to 1 years. And it's not until we get to the fifth category physical injuries, where ages 5 to 14 years or where the predominance of the burden of mortality lies. So there are many things killing children around the world unfortunately, but you can see if we look at the top six or seven, after that the rate or the importance of those subsequent causes tends to drop. The WHO has created this matrix to show major health risks to children. So across the top here, you'll see different types of outcomes. These are our top five leading causes of death in children and the rows in these tables correspond to the circular exposures that I highlighted in the previous graphic. So we can look and see for each of these types of exposures, there are different associations with the top five health outcomes. Now the dark turquoise colors on here indicate major contributors to health outcomes and the lighter turquoise indicate contributions that are significant or important, but don't rise to the level of being major. So for example, if we look at housing and shelter, you can see that exposure is highly associated or makes major contributions to perinatal disease, respiratory disease, insect-borne disease, and physical injuries. On the flip side, If we look all the way down to social and work environments at the bottom of the right-hand table, here we can see we have a different set of four factors that are making major contributions. So using a matrix like this, we can start to understand what aspects about a child's environment might be most strongly linked to particular health outcomes that we're trying to avoid like these top five leading causes of death among children globally. That's the WHO global perspective. What about here in the United States? If we went back in time about a hundred years to the early 20th century, infectious mortality or infectious disease was the predominant killer of children back then. Now we've advanced and we have the dominant causes of mortality being things like environmental chemicals, poor nutrition, and injuries from the physical environment. Those are sort of recognized hazards, but we also have to acknowledge the so-called new or emerging morbidities. These include things like asthma, autism, developmental delays, attention deficit hyperactivity disorder, cancer, injuries, changes to growth, and birth defects. Now just to come back and reinforce this notion, children really are more susceptible and more vulnerable to environmental hazards than virtually any other population on the planet. Recall that their relative dose when they're exposed is greater. They have a lower body weight and they breathe and drink more pound for pound than adults. They have better absorption. So remember the higher risk of nutritional deficiency, so low calcium, low iron intake can make for more lead exposure. And finally, children just tend to have greater exposures, period. They're lower to the ground. They have this disgusting hand-to-mouth behavior. And finally, they have this very exploratory behavior as they learn about the world around them. So for these reasons and many others, we need to consider children our most vulnerable population. And as a result of recognizing this issue, a lot of interventions tend to target children specifically. Because if we can make a positive impact on a child's life, that's going to have benefits for potentially decades down the road in terms of a more beneficial life trajectory.
