Sunday, June 14, 2015

Humans Poisoning Themselves With Mercury In Atmosphere & Ocean

It's already known, that by conservative estimates, humans have increased the concentration of mercury in the atmosphere by a factor three since 1850. Most of this has occurred by the burning of 'hard' fossil fuels such as coal and the mining of precious metals. Less well known is that  the atmosphere is a major source of mercury in the ocean. Thus, new research has shown it makes its way from the air to the sea, infiltrating marine food webs - so that this known neurotoxin can well end up on our dinner plates.

Now, Zhang et al in the journal Global Bio-Geochemical Cycles (2014), have determined that human activities have increased the amount of mercury in the oceans by 5 to 6 times.  To ascertain this, Zhang and his team set out to develop a model which would show how much mercury in the sea was part of the element's natural geochemical cycle and how much arose from human activity.

To achieve this, the Zhang team first had to determine the natural cycle of mercury, i.e. how the chemical circulated in the oceans in pre-industrial times, say before the mid-15th century.  They combined 3-dimensional simulations of mercury in the atmosphere, rivers and oceans before the year 1450 to explore how the element travels from the surface of the seas to the sediment.

Their model allowed the team to effectively recreate how mercury moves as well as varies - both horizontally and vertically - in the water. This then allowed for more accurate comparisons between the model's predictions and the observed mercury distributions. They thereby calculated that mercury stays in the water for an average of two thousand years before being embedded in sediment.

Based on these findings they could then generate maps showing the average concentrations of mercury in the oceans at several depths. They also compared their results to real samples from the Southern Ocean, the Atlantic Ocean and the North Pacific Ocean and found the amount of mercury actually present far exceeded what the model of natural mercury distribution predicted.

Most importantly, having set up the control model accurately, they were able to attribute the mercury excess to human activities - which have now increased the amount of mercury in the oceans by five to six times.

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