Leaves in Focus
The last several months have been particularly sluggish for conducting research due to this truly busy time in history. In the midst of dodging wildfires and surviving in a pandemic we have a few updates we would like to share with you.
Stomatal uptake of evaporated mercury is believed to be a major pathway of absorption by plants. Stomata are pores on leaf surfaces that regulate gas exchange such as the intake of CO2 and the release of O2.
Different plants have different metabolic pathways that can affect how they open and close their stomata which in turn may affect the amount of mercury that is absorbed. Additionally some forms of mercury are lipophilic and can directly be absorbed through the waxy coating on plant leaves (comprised mainly of cutin) and thus enter the plant in multiple ways.
So far we have seen leafy vegetables consistently have the highest mercury of tested produce. In agreeance with this we recently tested wild rosemary where the leaves and stems were processed and analyzed separately.
It was seen that the leaves had 10x higher total mercury concentration than the stems which supports our observed trend of leafy vegetables containing the most mercury. We plan on continuing to investigate key variables with leafy greens including grow time, stomatal closure, and waxy content of all crops grown along the coast.
Table 2. shows a tabulated data set of some of the most recent produce analyzed. Collectively the stone fruit (plums, pluots, etc) and peppers (chili, jalapeno) had the lowest levels of Hg (< 1 ppt) , whereas most herbs and leafy greens had 1-11 ppb of total Hg. It seems that leaf surface absorbs Hg much more than the fruit of any plant regardless of it being elevated off the ground (ex. plums) or low lying (ex. strawberries). A few veggies didn't seem to fit the pattern though, like the carrot was elevated in Hg, but it grows underground. More to learn, stay tuned!
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