We found a significant relationship between certain air pollutant emissions in 1999 and adjudications between 2003 and 2005 in Ohio counties. The magnitude of the association between air metal emission and adjudication was a 3–4% increase in risk for each natural log unit increase in emissions, with Mn and Hg emissions reaching statistical significance. PM2.5 and PM10 emissions were also significantly associated with adjudication with a 12–19% increase per natural log unit emission, respectively. Causality cannot be proven in observational studies such as this one, but the association warrants further examination in other research studies. Our negative finding of an association between the combined metals with adjudications may be due to the strong correlation among the metals.
Although our study cannot indicate a causal relationship between metal exposure and youth adjudicated for criminal activity, the literature supports this association, particularly for metals such as manganese and lead. Manganese is an essential element, and is considered one of the least toxic trace elements when consumed orally (Keen and Zidenberg-Cherr, 1996
; Nielsen, 1999a
); however, when inhaled manganese can travel directly to the brain through olfactory neurons (Dorman et al., 2002
; Leavens et al., 2007
) and cross the blood brain barrier through passive and active transport mechanisms (Aschner and Dorman, 2006
). Manganese exposed rats had an increased rate of fighting and other aggressive behavior (Chandra, 1983
). Occupational manganese exposure has also been linked with anxiety, aggression, impulsivity, emotional instability, psychoses, and fatigue (Collier, 1938
; Mena et al., 1987
; Mergler et al., 1994
; Penalver, 1955a
; Schuler et al., 1957
). Recently, hair manganese levels were associated with behavioral problems in children exposed through drinking water (Bouchard et al., 2007
). The biological mechanism of manganese on behavior may be its effects on brain neurotransmitters. Manganese lowers levels of brain serotonin and dopamine, both of which are associated with impulse control and planning (Kimura et al., 1978
; Masters et al., 1998
); low levels of brain serotonin are associated with disturbances in mood, poor impulse control and aggressive behavior (Retz et al., 2004
; Young and Leyton, 2002
We did not find an association between lead and youth adjudicated for criminal activity. This is in contrast to other researchers who found a positive association between lead exposure and aggressive and delinquent adolescent behavior (Braun et al., 2008
; Dietrich et al., 2001
; Needleman et al., 2002
; Nevin, 2000
; Pihl and Ervin, 1990
). Nevin (2007)
observed an association between preschool blood lead and subsequent international crime rate trends. A recent study by Wright et al. (2008)
found a positive association between developmental exposure to lead during childhood and adult criminal behavior in 250 young adults followed prospectively since birth in Cincinnati. Lead is known to potentially impact a large number of neurodevelopmental processes owing to the metal's ability to mimic calcium (Goyer, 1995
). One potential biological endpoint underlying the impact of lead on behavior is its apparent effect on brain volume in critical neurocortical regions. A strong association between aggression and reduced prefrontal cortical size has been demonstrated (Brower and Price, 2001
), and reduction in prefrontal gray matter has been associated with violent crimes in individuals with antisocial personality disorder (Raine et al., 2000
). Using volumetric Magnetic Resonance Imaging (MRI), Cecil et al. (2008)
observed that the brain region most affected by early lead exposure was the prefrontal gray matter. A study of Philadelphia youths enrolled in the Collaborative Perinatal Project found that the strongest predictor of arrest in males was a history of lead poisoning (Denno, 1990
). A survey of male children enrolled in the Pittsburgh Youth Study found that those with higher bone Pb concentrations had higher T
-Scores on the Delinquency and Aggressive clusters of the Achenbach Child Behavior Checklist (Needleman et al., 1996
). Higher bone lead levels have also been documented in a case-control study of adjudicated delinquents (Needleman et al., 2002
). Furthermore, in a similar cross-sectional ecological study, Stretsky and Lynch (2001)
found a strong association between air lead concentrations in all United States counties and homicide rates. One possible explanation for our lack of an association between airborne lead and adjudications is that tetraethyl lead in gasoline was phased out of use between 1976 and 1986, the primary source of airborne lead for the Stretsky and Lynch (2001)
population. Thus, the primary airborne source of lead for our juvenile population would have been from industrial emissions. Our study does not include other important routes of early exposure to lead, such as from deteriorating lead based paint.
We did not find an association between county estimated emissions and sociodemographic characteristics of median family income and percentage of family below poverty level, but we did find an association with percentage of African Americans. This finding may be explained by elevated emission concentrations in metropolitan areas containing a mix of high and low income populations. Since our analysis is limited to aggregate county data, we cannot further investigate the relationship between environmental air contamination and measures related to environmental justice, such as individual income, education, and race and ethnicity; however, using aggregate data, Mohai et al. (2011)
found a significant relationship between air quality in Michigan using emission data from the EPA's Toxic Release Inventory and school attendance and performance. Using individual residence, Brajer and Hall (1992)
found an inverse relationship with between ozone and fine particulate matter exposure and income in the South Coast Air Basin of California.
This ecological study has several limitations. Our analyses included aggregate county-wide data rather than individual biomarkers; thus providing a more blunt estimate of exposure. Our findings suggest that youth exposed to airborne manganese and mercury are at increased risk for criminal behavior and possible adjudication. Nevertheless, without an individual exposure matrix, we are not able to assert that there is a causal relationship.
Our exposure measures are based on the US EPA AirData. AirData contains monitoring data and reported emissions data, each with their own limitations. Although air monitoring data provides accurate measures of pollutants, the air pollution levels inferred for each county could be misinterpreted. The air captured for particle measurement may not represent the entire county or urban area air quality. The National Emission Inventory database for criteria and hazardous air pollutants compiles information from emissions inventories compiled by state and local environmental agencies, including the Toxic Release Inventory data. These emissions data are self-reported by the industry to the EPA. The National Emission Inventory database does, however, include stationary (point and nonpoint) and mobile (onroad and nonroad) sources.
Our analyses do not take into account other routes of exposure to metals other than airborne exposure. It was well-established that the hand-to-mouth behavior is a primary route of exposure to lead in small children and that early lead exposure is related to delinquency and adult criminality (Bornschein et al., 1985
; Wright et al., 2004
). In the US, the most significant route of lead exposure is from leaded paint residues in houses built before 1978, which was not captured by air emission data. Exposure to arsenic and cadmium is primarily via contaminated groundwater. Most mercury exposure in the United States comes from methylmercury after consumption of fish. Thus, our present data analysis likely underestimates
the amount of metal exposure in a portion of the population as the exposure source data does not include metal exposure sources from water, diet, home dust, or soil. Adjudication data may also underestimate the volume of youth crime. Adjudication data, however, is a reliable measure of serious crime committed by youths. Variation across jurisdictions may, however, influence actual counts.
The finding of particulate matter emissions and its relationship to adjudications is not surprising, as particulate matter is comprised of metals and other air pollutants, such as acids, organic chemicals, and soil or dust particles. Though the exact mechanism by which air pollution may result in neuroinflammation and neurodegeneration is unknown, four pathways have been proposed including: systemic inflammation leading to cytokine response and neuroinflammation, direct exposure to ultrafine particles (PM0.1), exposure to compounds bound to particulate matter, and CNS damage secondary to oxidative stress (Block and Calderon-Garciduenas, 2009