Mercury transport and human exposure from global marine fisheries

Abstract

Human activities have increased the global circulation of mercury, a potent neurotoxin. Mercury can be converted into methylmercury, which biomagnifies along aquatic food chains and leads to high exposure in fish-eating populations. Here we quantify temporal trends in the ocean-to-land transport of total mercury and methylmercury from fisheries and we estimate potential human mercury intake through fish consumption in 175 countries. Mercury export from the ocean increased over time as a function of fishing pressure, especially on upper-trophic-level organisms. In 2014, over 13 metric tonnes of mercury were exported from the ocean. Asian countries were important contributors of mercury export in the last decades and the western Pacific Ocean was identified as the main source. Estimates of per capita mercury exposure through fish consumption showed that populations in 38% of the 175 countries assessed, mainly insular and developing nations, were exposed to doses of methylmercury above governmental thresholds. Our study shows temporal trends and spatial patterns of Hg transport by fisheries. Given the high mercury intake through seafood consumption observed in several understudied yet vulnerable coastal communities, we recommend a comprehensive assessment of the health exposure risk of those populations.

Figure 1

Temporal trends (1950‒2014) of marine fisheries catches (dashed lines) and mercury exported (full lines). (a) Entire ocean (blue) and coastal (red) and high seas (orange) with breakpoint (circle) ± standard error (horizontal line). See Supplementary Table 1 for results of the segmented regressions. (b) Entire ocean (blue) and trophic levels (TL) rounded to the nearest integer: 4 (red), 3 (orange), and 2 (green).

Figure 2

Mercury export from the ocean. Mean total Hg export in (a) 1950–1969, (b) 1970–1989, (c) 1990–2009, and (d) 2010–2014 resulting from catches of fishes, molluscs, crustaceans, reptiles, and mammals for each MFA (numbers are provided in panel (a) and corresponding names are found in Supplementary Table 7). Standard deviations of means for each period are found in Supplementary Fig. 4. Maps were created in ArcGIS version 10.3.1 (http://desktop.arcgis.com/).

Figure 3

Temporal trends (1950‒2014) of catches (dashed lines) and Hg exported (full lines). China (red), Indonesia (orange), Japan (green), Peru (blue), and Chile (purple).