Residential Lead-Hazard Interventions, Childhood Anxiety, and Cognitive Impairment

Household interventions for secondary prevention of domestic lead exposure in children

BACKGROUND

Lead exposure is a serious health hazard, especially for children. It is associated with physical, cognitive and neurobehavioural impairment in children. There are many potential sources of lead in the environment, therefore trials have tested many household interventions to prevent or reduce lead exposure. This is an update of a previously published review.

OBJECTIVES

To assess the effects of household interventions intended to prevent or reduce further lead exposure in children on improvements in cognitive and neurobehavioural development, reductions in blood lead levels and reductions in household dust lead levels.

SEARCH METHODS

In March 2020, we updated our searches of CENTRAL, MEDLINE, Embase, 10 other databases and ClinicalTrials.gov. We also searched Google Scholar, checked the reference lists of relevant studies and contacted experts to identify unpublished studies.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs of household educational or environmental interventions, or combinations of interventions to prevent lead exposure in children (from birth to 18 years of age), where investigators reported at least one standardised outcome measure.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed all eligible studies for inclusion, assessed risk of bias and extracted data. We contacted trialists to obtain missing information. We assessed the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included 17 studies (three new to this update), involving 3282 children: 16 RCTs (involving 3204 children) and one quasi-RCT (involving 78 children). Children in all studies were under six years of age. Fifteen studies took place in urban areas of North America, one in Australia and one in China. Most studies were in areas with low socioeconomic status. Girls and boys were equally represented in those studies reporting this information. The duration of the intervention ranged from three months to 24 months in 15 studies, while two studies performed interventions on a single occasion. Follow-up periods ranged from three months to eight years. Three RCTs were at low risk of bias in all assessed domains. The other 14 studies were at unclear or high risk of bias; for example, we considered two RCTs and one quasi-RCT at high risk of selection bias and six RCTs at high risk of attrition bias. National or international research grants or governments funded 15 studies, while the other two did not report their funding sources. Education interventions versus no intervention None of the included studies in this comparison assessed effects on cognitive or neurobehavioural outcomes, or adverse events. All studies reported data on blood lead level outcomes. Educational interventions showed there was probably no evidence of a difference in reducing blood lead levels (continuous: mean difference (MD) -0.03, 95% confidence interval (CI) -0.13 to 0.07; I² = 0%; 5 studies, 815 participants; moderate-certainty evidence; log-transformed data), or in reducing floor dust levels (MD -0.07, 95% CI -0.37 to 0.24; I² = 0%; 2 studies, 318 participants; moderate-certainty evidence). Environmental interventions versus no intervention Dust control: one study in this comparison reported data on cognitive and neurobehavioural outcomes, and on adverse events in children. The study showed numerically there may be better neurobehavioural outcomes in children of the intervention group. However, differences were small and the CI included both a beneficial and non-beneficial effect of the environmental intervention (e.g. mental development (Bayley Scales of Infant Development-II): MD 0.1, 95% CI -2.1 to 2.4; 1 study, 302 participants; low-certainty evidence). The same study did not observe any adverse events related to the intervention during the eight-year follow-up, but observed two children with adverse events in the control group (1 study, 355 participants; very low-certainty evidence). Meta-analysis also found no evidence of effectiveness on blood lead levels (continuous: MD -0.02, 95% CI -0.09 to 0.06; I² = 0%; 4 studies, 565 participants; moderate-certainty evidence; log-transformed data). We could not pool the data regarding floor dust levels, but studies reported that there may be no evidence of a difference between the groups (very low-certainty evidence). Soil abatement: the two studies assessing this environmental intervention only reported on the outcome of 'blood lead level'. One study showed a small effect on blood lead level reduction, while the other study showed no effect. Therefore, we deem the current evidence insufficient to draw conclusions about the effectiveness of soil abatement (very low-certainty evidence). Combination of educational and environmental interventions versus standard education Studies in this comparison only reported on blood lead levels and dust lead levels. We could not pool the studies in a meta-analysis due to substantial differences between the studies. Since the studies reported inconsistent results, the evidence is currently insufficient to clarify whether a combination of interventions reduces blood lead levels and floor dust levels (very low-certainty evidence).

AUTHORS' CONCLUSIONS

Based on available evidence, household educational interventions and environmental interventions (namely dust control measures) show no evidence of a difference in reducing blood lead levels in children as a population health measure. The evidence of the effects of environmental interventions on cognitive and neurobehavioural outcomes and adverse events is uncertain too. Further trials are required to establish the most effective intervention for reducing or even preventing further lead exposure. Key elements of these trials should include strategies to reduce multiple sources of lead exposure simultaneously using empirical dust clearance levels. It is also necessary for trials to be carried out in low- and middle-income countries and in differing socioeconomic groups in high-income countries.