Preeclampsia and toxic metals: a case-control study in Kinshasa, DR Congo

Abstract

Background: Preeclampsia is frequent in Kinshasa (Democratic Republic of Congo), especially during the dry season. We tested whether preeclampsia was associated with exposure to environmental metals.

Methods: Using a case-control design, 88 women hospitalized with preeclampsia (cases) and 88 healthy pregnant women from the antenatal clinic (controls) were included in the study; 67 and 109 women were enrolled during the rainy and dry season, respectively. The concentrations of 24 elements were quantified by inductively coupled plasma mass spectrometry (ICP-MS) in 24-h urine collections. Differences in the urinary excretion of metals were investigated between cases and controls, and the interaction with season was assessed.

Results: Cases and controls were well matched regarding age, parity and duration of pregnancy. In controls, the urinary concentrations of most elements were substantially higher than reference values for adults from industrially developed countries, e.g. for lead: geometric mean (GM) 8.0 μg/L [25(th)-75(th) percentile 3.1-13.8]. The daily urinary excretions of 14 metals were significantly higher in women with preeclampsia than in control women, e.g. for lead: GM 61 μg/day (25(th)-75(th) percentile 8-345) in women with preeclampsia vs 9 μg/day (25(th)-75(th) percentile 3-21) in controls (p < 0.001). A significant interaction was found between season and preeclampsia for several elements, with higher urinary excretions in preeclamptic women than controls during the dry season, but not during the rainy season.

Conclusions: This study revealed not only that women with preeclampsia excrete higher amounts of several toxic metals, especially lead, than control women, but also that this excretion exhibits seasonal variation, thus possibly explaining the high incidence and seasonal variation of preeclampsia in Kinshasa. Although the exact sources of this exposure are unknown, these findings underscore the need for preventing environmental exposures to lead and other toxic metals.

Keywords: Developing country; Global health; Hypertension; Lead; Metal pollution; Preeclampsia; Seasonality.

Fig. 1

Map of Kinshasa with administrative entities and location of the General Hospital. I – V: geographical zones, as constructed here for statistical purposes. Zone I contains the historical center and business district of Kinshasa

Fig. 2

Meteorological data for 2011 in Kinshasa and daily urinary excretion of lead by pregnant women with and without preeclampsia. Upper panel: monthly rainfall (grey columns) and monthly averages of maximal (red line) and minimal (blue line) daily temperature in 2011 (Binza meteorological station). The light blue rectangle indicates the recruitment between March 1^st and April 18^th during the rainy season and the light yellow rectangle indicates the recruitment between July 1^st and September 2^nd during the dry season. Lower panel: individual values (with medians and 25^th and 75^th percentiles) of the daily urinary excretion of lead (Pb-U in μg/day) for pregnant women without (C, open symbols) and with preeclampsia (Ecl, full symbols), during the rainy season (light blue rectangle, left) and the dry season (light yellow rectangle, right). See Table 5 for significance levels