Lecture Notes: Oct. 28 (post-midterm)
Before the mid-term we covered material about natural resources, getting to p. 108. Post-mid-term material then starts with the “Sinks: Solid Waste Problems” on p. 108.
We moved this material fast, and it was only lightly dealt with in
lecture, in order to move on to the Population and Environment material (Chap
5), so that we’re caught up with the schedule.
Whether we are about to run out of a resource or not (the “source”
question), we’re still using a growing amount of raw material in modern
industrial society, and more and more attention is now paid to the “sink” end
of the line: how do we dispose of material resources? Humans have done this
throughout their history by creating dumps,
which today we call landfills.
Alternatively, some of our solid wastes can be incinerated. Finally, we can reduce the amount of waste by re-cycling material.
Solid wastes come from industrial sources, like mining and manufacturing,
and from “municipal” sources (including household and commercial sources). In
the past, before about the 1960s, there was less control over industrial
wastes, and they we often literally dumped on the ground either near the
source, in landfills, in oceans and lakes, or sometimes simply illegally out in
rural areas. The legacy of this dumping
is now visible in problems like toxic impacts on groundwater and human health
in places like Love canal, NY, a housing subdivision built on top of an
old chemical manufacturing site that
included an on-site dump, covered with a bit of soil. (we’ll return to this
story later).
Most municipal waste comes form household sources, and though these are
typically thought of as relatively benign:
60% of household is paper,
cardboard, yard
40% is glass, plastic, aluminum, iron, and other minerals
But some typical municipal wastes can create a toxic legacy. Household
wastes like paint, thinner, pesticides, petroleum products, etc. also end up in
the municipal waste stream and thus into landfills. While many places prohibit such wastes
disposal, it is hard to enforce such rules and people find there are very few
options for getting rid of hazardous waste.
The modern landfill is a big improvement over past practices, especially
in terms of lining that helps keep the material out of the soil ands
groundwater. The problem is that even seemingly benign wastes can breakdown in
a landfill into more toxic substances, as metals, plastics, and petroleum
products are “leached”out of the landfill by water
(rain and melting snow) percolating thru the pile. Modern standards require
that this “leachate” be contained and not allowed to
affect groundwater or soils. I illustrated this with slides of the Jefferson
County landfill, a well-run case where the debris pile is lined above and below
with impermeable materials, and leachate is collected
in pipes and allowed to evaporate in a pond. But, as Haper
writes, even well-managed landfills eventually leak a bit, and who is going to
take care of them over future decades?
Options: Incineration is growing, but faces severe problems---people do
not want to live near waste incinerators because they do release at least small
amounts of toxic materials. Incineration
is also very expensive, so only wealthier communities appear willing to try
it—the rest use typical dumps.
Recycling is important, but mostly applies to just a few key material wastes, like paper,
plastic and glass. About 24% of household waste is recycled or composted, and
re-cycling faces economic limitations.
The obvious key solution is
“source reduction” or “dematerialization.” Even recycled material eventually
ends up in the landfill, but if the total volume or mass is reduced at initial
extraction and production, then the total waste will decline. This could be less packaging, size reduction
(e.g., of cars), etc.
Chemical Pollution and
Toxic Wastes (pp. 111-119)
We really ran fast through this. Simply be aware of the main sources of:
Agricultural
pollutants:
Herbicides, Fungicides and Pesticides: various chemicals used to kill
diseases and pests that reduce crop production. While most everyone agreed
eventually that some pesticides, especially the long-lasting ones like the “clorinated hydrocarbons” (e.g., DDT) , had negative impacts
on ecosystems, modern agro-chemical pesticides, mostly “organophosphates”
degrade faster and don’t accumulate like DDT, but there’s still a debate over
their impact on the environment.
Fertilizer residues: the other main type of agricultural chemical
pollution is left-over nitrate and phosphate from fertilizers. Agricultural
fertilizers have caused great crop yield improvements, but there I some
tendency for over-fertilization which leaves residues that work their way into
surface and groundwater. Increased fertilization of surface waters causes what
Harper calls “cultural euthrophication” where
enhanced aquatic plant growth caused by over-fertilization depletes oxygen and
causes local waters to loose their ability to support many aquatic species.
Industrial Toxics:
The global production and consumption system inevitably produces toxic
compounds (keys ones here are heavy metals like lead and synthetic organic
compounds. Carefully managed and disposed of, these can be safely handled, but
accidents and neglect sometimes disperse them into air, water, and soil. The
heavy metals are especially known for the neurological impacts (neurotoxins) , while some subset of
synthetic organic compounds used
industry are carcinogens
(cancer-causing agents) and mutagens
(cause genetic damage and defects).
Harper does not mention it but I also mentioned in class teratogens,
chemicals that tend to cause birth defects in mammals.
Many uncertainties with these pollutants:
1. As Harper points out,
it is difficult in many cases to link a particular chemcial
to adverse health effects, which may take some time to emerge in an exposed
population.
2. Not all synthetic
chemicals are harmful, but testing takes a lot of time and we have not tested
the toxicity of many compounds in current use.
3. Even when tested,
scientists disagree with their toxicity.
We only discussed one form of municipal pollution, waste water or sewer.
In the MDCs, including the US, most wastewater is
treated to remove solids and degrade organic pollutants and diseases. Even this
creates solid waste or “sludge” that is either applied to farmland as
fertilizer or is placed in conventional landfills.
Ship the rest of this chapter so that we can get caught up on the
population issue.