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This stylized diagram of the effects of nutrients and non-nutrients on metabolic efficiency illustrates the similarities and dissimilarities of the two. The absence and deficiency of a nutrient or essential element, such as iron, results in death at very low concentrations and failure to attain optimal health (metabolic efficiency) at sub-optimal concentrations. Conversely, the absence or low concentration of a non-nutrient, such as DDT, has no adverse health effect and metabolic efficiency may be optimal. That condition may be achieved when all essential nutrients are present in amounts that fulfill all metabolic requirements. However, both nutrients and non-nutrients begin to cause adverse health effects when they exceed certain concentrations and death at higher concentrations. To date, the only material with no recognized adverse health effect is chocolate ice cream. Concentrations in those upper regions are referred to as the NOEL (no adverse effect level), LOEL (lowest observed effect level), and LOAEL (lowest adverse effect level). The latter two are different because a chemical may cause an observable effect that does not measurably impact the health of an organism (e.g., a change in pigmentation may not be especially attractive, but it may not be unhealthy). |
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The "classic" equation for the photosynthetic
conversion of inorganic carbon into organic carbon (biomass)
by marine microscopic plants (phytoplankton), with a little
iron thrown in. While the importance of trace elements was
not even recognized when I was a graduate student (nitrogen
and phosphorous were the "limiting nutrients" for primary
productivity), it has subsequently been demonstrated that
iron is a limiting nutrient for phytoplankton in some
oceanic regions. This concept was pioneered by John Martin,
who facetiously proposed (on Good Morning America) the
"Geritol solution to global warming" [Geritol was a tonic
for aging (i.e., geriatric) that contained iron and alcohol
(i.e., ol), which may explain why grandma was so happy at
Thanksgiving]. Unfortunately, the press did not understand
John's humorous proposal that the complex problems of global
warming could be solved with an iron pill for the oceans,
and John was subjected to a substantial amount of
inappropriate criticism before he passed away. Fortunately,
his research was subsequently substantiated with a study
that added iron to surface waters in the tropics, which was
conducted by Ken Bruland and Mark Wells (who made this
figure) of UCSC and Kenneth Coale and Ken Johnson of Moss
Landing Marine Laboratories, where John was the director.