Summary for Wednesday February 17th

Today marked the beginning of material that will be on the final but not the midterm and a continuation of our water quality discussion. We started off with a look at the nitrogen cycle, nitrogen bioavailability, and the role of nitrogen in sustaining life. Nitrogen is the limiting agent in many (all?) agricultural systems and so we use natural gas and atmospheric nitrogen (N₂) to make synthetic nitrogenous fertilizers which we then apply to crops in order to increase productivity. The synthetic nitrogenous fertilizer that is not absorbed by plants ends up entering surface and groundwater systems and can result in water quality issues. When this bioavailable nitrogen enters natural systems that are nitrogen limited, algal blooms can occur which create hypoxic conditions that can lead to fish kills. The Gulf of Mexico and the Chesapeake Bay are two locations that are currently experiencing seasonal algal blooms related to nitrogen runoff. Excess bioavailable nitrogen is also responsible for increased rates of eutrophication in surface waters. The human health effects of excess bioavailable nitrogen include decreases oxygen carrying capacity of blood (methemoglobinemia = blue baby syndrome), decreased thyroid gland function, and cancer.

We then spent some time summarizing a recent article in the NY Times (That Tap Water Is Legal but May Be Unhealthy). The two main points of the article are that

the EPA only regulates a small number of the 60,000 chemicals that are used in the USA, and

some of current standards (MCLs) are high enough that you can be drinking water that is unhealthy but does not violate any laws.

Arsenic (As) presents a good example of the second issue posed above. As is a chalcophile (sulfur loving) element that occurs in naturally sulfur-rich rocks. As can also be concentrated anthropogenically through industrial processes and mining (many of the metals that we mine occur as sulfide minerals). The acute toxicity of As has been know for a long time (as little as 100ppm of As is acutely toxic) but more and more research has shown that smaller and smaller doses of As can be unhealthy. In 2001, the the EPA lowered the legal limit for As in drinking water from 50ppb to 10ppb (the new limit did not go into effect until 2006). 50ppb has been linked to rates of cancer at ~1/100. 10ppb has been linked to rates of cancer at ~1/600. Both of these numbers are well below the "acceptable risk" of 1/1 million. Some research even shows negative health effects at 1ppb As. New England, particularly the Seacoast area of New Hampshire is an example of an area with naturally As-rich rocks and there are an estimated 13 million people in this area whose water became illegal with the lowering of the standard from 50 to 10 ppm. Most of the numbers in this paragraph come from the Dartmouth College Toxic Metals Research Program.

Bangladesh is another example of a region with As groundwater problems. Bangladesh is also troubled by surfaces water quality problems and began using groundwater wells a few decades ago- only to discover that their soils are naturally As rich. We will discuss their plight further in class on Friday.

Terms/concepts to know from today's lecture: bioavailability (biologically available), limiting agent (nitrogen limited), eutrophication, acute toxicity, acceptable risk, and ppb.

For lecture on Friday, please read:

Dissolved Arsenic in Bangladesh Drinking Water Is from Human Alteration of Landscape

The abstract for the original paper in Nature Geosciences that is discussed in the article above is here.

Slides shown in lecture today have been posted as a .pdf to Sakai.

The midterm is due Friday.

I also want to remind people that there is an outside lecture opportunity tomorrow (Thursday) nigh: "Nothing New about NAFTA: North American Connections and Their Historical Lessons" (aka Ecology of US-Mexico Trade) by Sterling Evans, University of Oklahoma; Thursday February 18, 2010 7:00 PM in Northern Auditorium, Leyburn Library.