Spatial and temporal distribution of p,p'-DDE (1­dichloro­2,2­bis (p­chlorophenyl) ethylene) blood levels across the globe. A systematic review and meta-analysis.

BACKGROUND: Although p,p'­DDT (1,1,1­trichloro-2,2­bis (p­chlorophenyl)­ethane) has been banned for decades in most countries, its major metabolite p,p'-DDE (1­dichloro­2,2­bis (p­chlorophenyl) ethylene) is still detected in the vast majority of human blood samples. OBJECTIVES: The purpose of this study was to quantitatively estimate the geographical distribution of DDE blood levels and record time-trends for specific countries and continents, exploiting available data from the scientific literature. METHODS: A literature search was performed in SCOPUS and PUBMED databases. Studies were screened at 2 levels applying different sets of inclusion/exclusion criteria. Blood levels of DDE along with other variables of interest were extracted, and a meta-analysis of random effects was conducted, by using the package metafor within the statistical programming language R. Results were expressed as pooled geometric means (GM [95% confidence intervals, CIs]). RESULTS: A total of 418 papers were included in the quantitative synthesis that contained data for 854 population subgroups, and analyzed a total of 195,595 samples. Overall global DDE concentrations dropped from 5207 (95% CI: 3616-7499) ng/g lipids during 1951-1969 to 207 (95% CI: 159-269) ng/g lipids for studies reporting sampling after 2000. Analyses for studies published from 2001 and onward revealed geographical differences regarding DDE burden. DISCUSSION: The significant decline in DDE blood levels after its restriction is demonstrated in our results. Differences in decrease trends were observed in different parts of the globe, which can be explained by deferred implementation of environmental policies. In some countries DDE concentrations remain high, and systematic biomonitoring is proposed.