Caribbean Lead and Mercury Pollution Archived in a Crater Lake

Lead
and mercury have long histories of anthropogenic use and release
to the environment extending into preindustrial times. Yet, the timing,
magnitude, and persistence of preindustrial emissions remain enigmatic,
especially for mercury. Here, we quantify tropical lead and mercury
deposition over the past ∼3000 years using a well-dated sediment
core from a small crater lake (Lake Antoine, Grenada). Preindustrial
increases in lead and mercury concentrations can be explained by varying
inputs of watershed mineral and organic matter, which in turn reflect
climate-driven changes in the lake level. We find no evidence that
preindustrial lead and mercury use raised deposition rates in this
remote ecosystem, and our results underscore the need to carefully
evaluate common normalization approaches for changing lithogenic inputs
and sedimentation rates. Industrial-era lead and mercury accumulation
rates in Lake Antoine have been accelerated by land use and land cover
change within the crater rim, yet global industrial pollution remains
evident. After correcting for watershed inputs, we find that recent
atmospheric lead and mercury deposition rates averaged 2925 and 24
μg/m2/y, respectively, which are in close agreement
with monitoring data. Our results challenge recent assessments suggesting
preindustrial mercury use raised atmospheric deposition rates globally,
highlighting the unique nature of 20th Century industrial pollution.