Regulatory interventions
In total there were 21 regulatory interventions covering four types of exposures: airborne pollutants, lead paint, water pollution, and pesticides (see Table
1).
Outcomes: Regulations of vehicle fuels and emissions standards were the most commonly studied form of policy intervention addressing airborne pollutants, making up over half of the 11 included articles. Bahadur 2010 studied increasing restrictions on diesel fuel in California using data collected by the California Air Resource Board to show a statewide decline in black carbon levels [
19]. Davis 2012 focused on reductions over time in allowed vehicle carbon monoxide levels to show that multiple pollutants measured by the California Air Resource Board declined with increasingly stringent regulation, even when controlling for reduced driving during recessions [
25]. Two studies specifically considered changes in vehicle emissions controls standards [
21,
26]. Both collected data on particulate matter and other pollutants using road sensors, one in three different cities (Pokharel 2013) and one at multiple sites around greater Los Angeles (Bishop 2013). Both studies showed decreasing levels of pollutants over time with the implementation of increasingly stringent air quality standards. Two other studies reviewed requirements to retrofit or replace vehicles that had been identified as key sources of pollutant exposure. Mott 2002 focused on the requirement to add catalytic converters to U.S. vehicles and showed steady reductions on carbon monoxide-related deaths using national death certificate data over more than 30 years [
24]. Dallman 2011 assessed air quality by measuring multiple pollutants released into the air above diesel trucks entering the Port of Oakland before and after the implementation of a requirement to retrofit truck filters or replace older trucks with new vehicles. It found a significant decrease in levels of measured pollutants [
16].
The remaining studies reviewed broader air quality interventions. Three studies specifically considered policies that required reductions in nitrogen oxides emissions. Gego 2007 used data drawn from federal monitoring sites in the eastern United States and found reductions in ozone levels despite incomplete implementation of the law [
22]. Aleksic 2013 specifically assessed ozone levels in New York before and after implementation of the standards using data from federal monitoring sites and also found significant declines [
23]. Lin 2013 specifically assessed a nitrogen oxides emissions reduction Budget Trading Program, which was correlated with a decline in hospitalizations based on a respiratory diagnosis after implementation [
18]. Cheung 2005 sought to assess the effects of a range of air quality regulations implemented over time. This California-specific study in the Los Angeles Basin found reductions in particulate matter over time [
20]. Thomas 2013 measured sulfur levels in juniper trees after the implementation of the Clean Air Act, and found both reduced emissions and a recovery in the health of the trees [
27].
Contextual factors and mechanisms: The theory behind regulatory interventions is that removing products that expose individuals and the environment to toxins associated with adverse health outcomes will reduce or eliminate that exposure. Context and mechanism were not systematically discussed in these studies. When they were discussed, most attention was paid to the problems with describing the context in which interventions were made.
Regarding context, all of the interventions took place in the United States, and were measuring outcomes that could be affected both by the specific interventions studied and by additional regulatory changes, which typically occurred at the federal level. Many of the studies did not attempt to describe the effects of specific interventions, assuming instead that the combined effect of additional regulations was causally related to the outcomes of reduced pollutant levels. This assumption was not always plausible. For example, Lin 2013, which focused on hospital admissions for respiratory diseases in the wake of nitrogen oxides regulation, noted that the simultaneous passage of a New York state clean air law targeted at tobacco use was also likely to have affected the outcome measure [
18].
The specific mechanisms triggered by the interventions were rarely described. For some of the studies, those in compliance or out of compliance with regulations may not have been aware of the implications of their behavior at all.
Interpretation: The studies included rarely provided an assessment of individual interventions, making it difficult to draw definitive conclusions about the effectiveness of particular policies. Although all of the studies of air quality regulations were correlated with reduced levels of airborne pollutants using multiple measures, most of the study designs did not allow an assessment of which interventions led to changes in outcomes. The confounding factors of multiple simultaneous interventions that were not measured were noted in many of the studies.
Nevertheless, some studies specifically assessed changes in measured pollutants before and after the implementation of individual interventions. Studies at the local and regional level that reviewed air quality measures before and after the implementation of specific interventions suggested that two kinds of interventions reduced exposures: (a) those requiring retrofit or replacement of known producers of airborne pollutants (e.g., fuels, filters, vehicles), and (b) interventions that required reductions in the levels of certain pollutants as independently verified by federal monitoring, but that allowed state and local governments to choose the mechanism by which to achieve these reductions.
These studies suggest that the findings of the larger national studies, although they lack controls for effect modifiers, may be valid as well. Interventions that eliminated known sources of airborne pollutants reduced environmental exposures. Where federal monitoring was in place to measure air quality outcomes, interventions that established a maximum standard and allowed states and localities to develop their own plans to meet it also appeared to be successful. All of the regulatory studies of airborne pollutants showed that regulatory interventions at least partially reduced exposures.
Outcomes: The four studies considered multiple interventions that could reduce lead exposure. Rich 2002 tested cleaning techniques, comparing standard practices to more or less intensive methods. While all of the interventions reviewed were successful in reducing lead dust measured on hard surfaces, the combination of cleaning with TSP (trisodium phosphate) and vacuuming with a HEPA (high-efficiency particulate air) filter was most effective [
28]. Brown 2001 compared strict enforcement of lead testing and remediation housing policies in one state to less-strict enforcement in a second state, and determined that the stricter enforcement was associated with lower blood levels of lead as well as higher property values [
30]. Galke 2001 used multiple sites to review a range of HUD (US Department of Housing and Urban Development) interventions developed by local governments; these interventions were not described in detail. The study included an assessment component and determined that all measures reduced exposures, and that lower-intensity interventions that did not include abatement could also do so [
31]. Breysse 2007 reviewed lead treatments required in the city of Baltimore by law, including an assessment of whether visual inspection was sufficient to identify risk. The study suggested that visual inspection was significantly less effective than testing of hard surfaces, and that although lead dust levels declined after remediation they remained above recommended levels [
29].
Contextual factors and mechanisms: Context and mechanism were not described in detail in these studies. None of the three studies that discussed local interventions (Brown 2001, Galke 2001, Breysse 2007) specifically detailed the interventions that were used to reduce lead exposure. Although Brown 2001 proposed that stricter enforcement could reduce lead exposure, the authors noted that the direction of causality for the finding of association was unclear. It is possible that areas with higher property values had more resources available for enforcement as well as for remediation of lead risks [
30]. The Rich 2002 study of cleaning techniques noted that HEPA-filter vacuums, although they reduced exposure, were both more expensive and more difficult to purchase in poor, urban areas where the risks of lead exposure were higher. As an alternative, the authors noted that more frequent cleaning could compensate to some extent for less effective equipment [
28]. The Breysse 2007 study of lead remediation interventions in Baltimore suggested that objectively measuring of outcomes through testing was more effective than visual assessment by inspectors [
29]. Consistent with this finding, the Galke 2001 multi-site study of local interventions that showed a range of interventions reduced exposure also included an assessment component [
31].
The mechanisms, or reactions triggered by the interventions, were not described in any of the four studies, although the authors of the Rich 2002 study of cleaning methods speculated about possible public responses to a change in recommendations based on their findings. The authors of the Brown 2001 enforcement study advised directing more resources toward stricter enforcement of lead abatement policies, but competing priorities for those resources were not described, as this proposal was hypothetical. The mechanisms in the other two studies could not be described because the interventions themselves were not fully described.
Interpretation: The studies of regulatory lead paint abatement interventions suggest that these interventions can reduce exposure. Stricter enforcement and testing were associated with reduced exposure, as well as more intensive remediation efforts. As with regulatory interventions in other areas, monitoring results and requiring removal of known pollutants improved outcomes.
Outcomes: Regulatory interventions that sought to address water pollution were divided in terms of scope, with two studies (Lakind 2010, Hundal 2014) reviewing national-level outcomes and the rest reviewing regional data. The national studies included one study of environmental exposure in humans. After the implementation of a new drinking water disinfection rule that requiring the reduction of pollutant levels post-treatment, Lakind 2010 used national blood sample data drawn from NHANES (The National Health and Nutrition Examination Survey), found that one of the targeted pollutants decreased in the blood samples but the other targeted pollutants did not [
36]. Hundal 2014’s study of the Clean Water Act assessed trace metal levels in sludge after implementation using EPA data and found both that trace metal concentrations declined significantly and that the post-implementation sludge could be classified as “exceptional quality” [
34]. Kauffman 2011 assessed multiple interventions, including not only federal water quality standards but the establishment of sewage treatment plants and phosphate detergent bans. Using data collected by USGS monitoring stations, it found that overall water quality along the Delaware River significantly improved, and measured levels of multiple pollutants declined [
33].
The other studies specifically considered state-level interventions to reduce water pollution. Dorsey 2010’s study of the California Clean Beach Initiative measured water quality at multiple sites that had successfully bid for grant funding to develop programs to improve local water quality. Fecal indicator bacteria were measured before and after the program implementation and the interventions with the greatest reductions were assessed as evidencing the best intervention practices [
32]. Daberkow 2001’s study of Nebraska’s efforts to meet federal drinking water standards through a fertilizer management program showed that providing advice on appropriate usage levels led to a decline in fertilizer use and associated pollutants, but that both remained above recommended levels [
35].
Contextual factors and mechanisms: As in other areas of exposure, context and mechanisms were not systematically discussed in these studies. Similar to the studies of airborne pollutants, the main consideration was the context in which interventions were made.
The studies of regulatory interventions targeting water pollution were evenly split between assessments of national policies and state policies. The efforts to assess context are hampered by the fact that only one of the studies of national policies, Lakind 2010, could describe the effects of specific interventions. For two studies (Kauffman 2011, Hundal 2014) the period of analysis included implementations of multiple interventions. Studies of state-specific policies (Dorsey 2010, Daberkow 2001) were better able to assess the effects of specific interventions. Studies of both national and state interventions were more successful in measuring outcomes when data that could measure compliance were available or when data collection had been built into the intervention. Lakind 2010’s study of changes in blood pollutant levels after the establishment of new drinking water disinfection standards was sponsored by the industry that developed the new disinfection process; the effect of this potential conflict of interest was not discussed by the authors [
36].
The mechanisms triggered by the interventions were not fully described. The studies that included multiple interventions (Kauffman 2011, Hundal 2014) could not disentangle mechanisms, even if there had been an effort to describe them. Studies that use anonymized national data on human exposure such as NHANES, like Lakind 2010, cannot assess the reaction even to specific interventions. Studies of single interventions (Dorsey 2010, Daberkow 2001) may also find that the reactions triggered by the intervention were not those that had been anticipated. Daberkow 2001 relied on providing advice to farmers as a means to reduce fertilizer use, but noted that this advice was undercut by the farmers’ overly optimistic assessments of expected crop yields, which led to continued over-fertilization and as a result, to unexpectedly high levels of water pollution [
35]. Studies of interventions that provided a strict standard, measurable outcome data, or a clear enforcement mechanism showed reductions in pollutants, possibly by making the implications of meeting or not meeting the regulatory standard apparent.
Interpretation: The five studies on water pollution interventions showed the anticipated results for some interventions. Studies that considered multiple interventions could not determine the effectiveness of any particular policy. Even when a specific policy could be studied, as in the case of a new drinking water disinfection method in Lakind 2010, the study showed mixed results. Moreover, the Lakind 2010 study was funded by the organization that created the disinfection process, which raised issues of potential conflict of interest.
The studies of specific state-level interventions suggested that monitoring of outcomes may identify policies that reduce measured pollutants. Dorsey 2010’s study of the California Clean Beach Initiative monitored five types of interventions proposed by local agencies for funding and was able to determine which intervention was associated with the greatest decrease in fecal indicator bacteria (diversion and a combined approach). Daberkow 2001 found that efforts to decrease fertilizer use in Nebraska by providing advice to farmers, which did not require changes to behavior or link reductions in fertilizer use to incentives or monitoring, were less effective.
Outcomes: Clune 2012’s study, which was national in scope, found that measures of pesticide concentrations in urine declined significantly after implementation of the new standard [
37].
Contextual factors and mechanisms: Clune 2012 noted that use of a national dataset made it difficult to determine the exact cause of changes in human exposure levels. Their analysis did not indicate whether the change in law was the proximate cause of the reduced exposure in humans, as it was possible (although unlikely) that producers and consumers decided independently to stop using all types of pesticides prior to the implementation of the law eliminating sales of OP insecticides. However measures of other environmental exposures in the same population suggested that the use of unrestricted pesticides did not decline, as the human exposure outcomes associated with the use of these chemicals did not decline. The mechanism, or reactions to the intervention, was not assessed; as noted above, this is rarely possible when using an anonymized dataset to measure human exposures.
Interpretation: Consistent with findings from regulatory interventions in other areas, banning the sale of a product known to be associated with health risks reduced exposure.
Educational interventions
The review included two studies that considered education interventions, which addressed two types of exposures: lead paint (Aschengrau 1998) and water pollution (Postma 2011).
Study characteristics: The two educational studies assessed efforts to teach families how to reduce their environmental exposures. Aschengrau 1998 was a controlled trial that sent outreach workers to the intervention group to teach caregivers how to clean housing units where children were exposed to lead paint [
38]. Postma 2011, a cross-sectional survey, encouraged families to test well water for contaminants [
39]. The Aschengrau 1998 study of lead remediation instruction reviewed measures of environmental exposure (hard surfaces testing) as well as human exposure (blood levels) before and after the intervention. The Postma 2011 study of well water contaminants assessed measures of environmental contamination after the intervention.
Outcomes: The Aschengrau 1998 educational intervention that sought to address lead paint exposure was assessed at the local level, in the city of Boston. Outreach workers made a home visit to participants in the intervention groups to educate caregivers how to remove lead dust through cleaning in order to reduce exposure, but after the intervention, researchers found that caregivers did not complete all of the suggested cleaning, particularly in window wells. The intervention was only effective for children that had severely high lead levels, and showed no effect or a negative effect in less severe cases [
38]. The Postma 2011 study of well water contaminants after an educational outreach effort in Montana and Washington found that 27 % of households tested positive for at least one contaminant post-intervention, and that 89 % of wells contaminated with coliform in the first test were still contaminated with coliform at retest. Higher socioeconomic status was correlated with higher testing rates before the intervention, and with a lower risk of exposure to pollutants [
39].
Contextual factors and mechanisms: The theory behind educational interventions is that informing the populations at risk of their exposure and of remediation strategies can change behavior in such a way that exposure levels decrease. The educational intervention studies addressed context more than the studies of regulatory interventions. The targeted populations of these interventions were at higher risk, due in many cases to poverty. Although the need for protection from environmental exposures in these groups is higher, because their living situations are more likely to expose them to pollutants, their ability to remediate these risks is lower due to limited resources.
The mechanism, or the reaction to the intervention, suggests that the value of educational interventions may be limited. Caregivers targeted by the lead paint educational intervention studied by Aschengrau 1998 did not complete the suggested cleaning strategies, leaving children at risk of continued exposure to lead. The studies of lead paint regulatory interventions, discussed above, suggest that these caregivers may not have had the resources available to clean as advised. Similarly, the efforts by Postma 2011 to provide information about well water contaminants did not necessarily lead to remediation, given that nearly 90 % of households with well water contaminated by coliform on the first assessment still had contaminated water on the second assessment. In both cases, there was inadequate response to the intervention, suggesting a broken mechanism. This may have been caused by an incomplete understanding of the context in which interventions were undertaken.
Interpretation: Educational interventions did not appear to reduce exposure to environmental hazards. Both efforts to educate individuals exposed to environmental toxins, with the expectation that they could remediate these risks themselves, were unsuccessful. This failure may reflect the fact that individuals at highest risk of exposure are also least likely to have the resources available to pursue remediation.
Economic interventions
The review included two studies that considered economic interventions, which addressed two types of exposures: airborne pollution (Lu 2012) and hazardous waste (Eagan 2002).
Study characteristics: Lu 2012 considered the effects of changing natural gas prices relative to regulation on national sulfur emissions levels, after passage of the Acid Rain Program and cap-and-trade regulation [
40]. Eagan 2002 assessed a purchasing tool that provided information on mercury levels in products for reducing waste mercury production by health care facilities in the Great Lakes region [
15]. Both studies reviewed measures of environmental exposure, specifically sulfur emissions tracked by the EPA (Lu 2012), and the extent of mercury waste produced by health care facilities in the study sample (Eagan 2002).
Outcomes: The economic intervention study by Lu 2012 assessed the effect of changing natural gas prices relative to national regulation on sulfur emissions and was conducted at the national level. Lu 2012 found that the drop in sulfur emissions was attributable to the regulatory interventions rather than the economic effects of changing natural gas prices [
40]. Eagan 2002’s study of hazardous waste focused on developing a tool for health care facilities in the Great Lakes region to voluntarily reduce mercury waste by purchasing products that contained lower levels of mercury. The intervention developed was a purchasing tool sent to suppliers which provided information on the mercury levels in each product, combined with an incentive payment that encouraged participating health care facilities to pilot use of the tool. After the intervention, new purchases reduced mercury waste both in durable equipment (a permanent reduction) and in annual purchases (an annual and ongoing reduction). Five of the nine participating health care facilities stated that they would continue to use the purchasing tool in the future [
15].
Contextual factors and mechanisms: The theory behind economic interventions is that changing the relative prices of products that produce lower environmental exposures can change behavior. The context for these interventions suggests that this theory may be borne out in some circumstances but not others. In the national study conducted by Lu 2012, an external economic intervention did not change environmental exposure, and given the aggregate nature of the data, it is difficult to interpret the context, which probably varied substantially based on the types of purchasers. The regional study by Eagan 2002 focused on health care facilities that voluntarily enrolled in a purchasing program intended to reduce hazardous waste, and provided a financial incentive for them to learn to change their purchasing behavior. In addition, it targeted a population—purchasing departments—with specific experience in economic interventions.
The mechanism, or reaction to the intervention, reflected the different populations included in the studies. The population that voluntarily enrolled in the Eagan 2002 study was responsive to the intervention, and changed behavior to reflect the goal of reducing waste mercury. Even so, nearly half of the participants stated they would no longer use the intervention after the end of the study and its incentive payments. The population subject to a natural experiment in Lu 2012—changing gas prices—was not responsive to the economic intervention. The contemporaneous regulatory interventions appeared to have more effect in reducing exposures.
Interpretation: The studies of economic interventions suggest that they only work in certain contexts. With a population that volunteered to test an intervention in Eagan 2002, engagement with the process was high and the effect was to reduce hazardous waste. Measurement of exposure and of outcomes provided feedback to participants about what strategies would be successful. The economic intervention studied by Lu 2012 that relied on a natural experiment with gas prices was less successful. Although it was impossible to assess the mechanism, it is unlikely that the intervention, in the form of higher prices, was viewed as a means to reduce exposure to environmental toxins. Moreover, any effects of the intervention on exposure levels would not have been evident until well after the fact. Economic interventions appear to be most appropriate when used in populations that are willing to change behavior but lack information. Even in these circumstances, continuing subsidies may be required to maintain full participation.