The Mississippi
River is one of Louisiana's most important resources. Its
sediments built our marshes and swamps and the nutrients it
carries fertilize the waters of the Gulf of Mexico. The river
provides a significant fishery and serves as a source of drinking
water. To rebuild deteriorated marshes, several freshwater
diversions from the river into the marshes are currently in
operation and even more are planned. The environmental health
of the river is obviously important. Some individuals and
groups view the river as a giant sewage ditch loaded with
pollutants and toxins. Others see it as a valuable resource
whose waters and sediments are vital to Louisiana's coastal
restoration effort. The Mississippi River has been extensively
studied by the U.S. Geological Survey (USGS) and the Louisiana
Departrnent of Environmental Quality (LDEQ). The results of
this monitoring and research are as follows:
Heavy
metals. These are elements such as iron, copper,
zinc, uranium, cadmium, lead, and mercury. Some are needed
in the diets of humans. Others, such as lead, mercury and
cadmium, can be poisonous when they occur in high concentrations.
Some heavy metals are contributed to the Mississippi River
by natural processes such as erosion, but it is estimated
that mining adds ten times as much to the water as is natural.
Most heavy metals are not dissolved in the water but are attached
to sediment particles carried by the river.
Generally
speaking, concentrations of heavy metals decrease the farther
down the river that samples are taken. Overall, concentrations
of heavy metals dissolved in the 1700 miles of the river are
well below legal guidelines. However, many individual sample
locations showed levels of heavy metals in river sediments
that were higher than those allowed by pollution guidelines.
LDEQ sampling of fish in the Mississippi River in Louisiana
found mercury, the heavy metal of most concern, in 84 percent
of the samples, though at very low levels. The average level
for all fish samples was one-eighth the alert level and the
highest amount found in any single fish was still well below
guidelines.
Nutrients.
These are elements such as nitrogen and phosphorus
that are used by plants in their growth. An oversupply of
these nutrients can cause increases in algae growth, and an
overabundance of algae can cause taste and odor problems in
drinking water. Also, when algae die, their decay can cause
oxygen shortages that kill or stress fish and also change
the chemistry of the water in ways that allow heavy metals
to move out of sediment into the water. Nutrients can come
from many sources, including human and animal wastes, household
cleaners and detergents, lawn and crop fertilizers, and industrial
wastes. USGS studies estimate that 75 percent of the nutrients
currently carried by the river are from human activities.
Nitrogen, in the form of nitrates, is the nutrient of most
interest. High nitrate levels river water are the suspected
cause of events such as the hypoxic area (dead zone) in the
Gulf and the 1997 toxic algae bloom in Lake Pontchartrain.
Nitrate levels in the river have increased since the turn
of the century and are considered very high.
Pesticides.
The USGS estimates that two-thirds of all pesticides used
for agriculture in the U.S. are applied in me Mississippi
drainage basin, and that about 3 percent of them end up in
the water. The states of Iowa and Illinois are the main sources.
Modern agricultural pesticides break down relatively quickly
and do not accumulate in animals as much as those used years
ago. The average annual concentrations of all pesticides measured
in the Mississippi River are well below health-based limits
and do not violate the Safe Drinking Water Act. LDEQ fish
sampling did show some pesticides in fish flesh. Dieldrin
was found in one composite sample in a concentration of 0.80
ppm, which is above the FDA alert level of 0.30. The good
news is that the overall average of dieldrin for all the samples
was only 0.01. At this level of concentration, the risk of
a person getting cancer from eating one eight-ounce meal of
Mississippi River fish per week for 70 years is about 1 in
10,000.
Chemicals.
The USGS conducted a study on four chemicals: PCBs,
chlordane, DCPA (chlorthal), and hexachlorobenzene. Although
PCBs and chlordane were banned some time ago, they still persist
in the environment. DCPA has been so widely used that its
sources cannot be pinpointed. Some PCBs and chlordane were
found in almost every sediment sample taken. The Ohio River
contributes the largest share of these chemicals to the Mississippi
River. DCPA was also found widely throughout the river, but
hexachlorobenzene, in contrast, has more specific sources.
Five times as much comes in from the Ohio River than from
any other source on the upper Mississippi River. In the lower
river, significant concentrations of the compound are added
to the Mississippi River as it flows through the industrial
area between St. Francisville, Louisiana, and New Orleans.
Because these chemicals can concentrate in living animals,
catfish were sampled up and down the river. None of the chemicals
were found in high enough concentrations in fish to be of
health concern. PCB levels in catfish were highest in the
upper Mississippi River and in the Ohio River. LDEQ fish sampling
showed that the average amount of PCBs in river fish was only
four-one thousandths of what would be needed for a health
alert. Chlordane was highest in the Ohio River and in the
Mississippi River in Missouri. The highest concentration of
hexachlorobenzene was in fish from the Mississippi River near
Luling, Louisiana. DCPA concentrations in fish were found
to have gone down slightly during the years from 1976 to 1981.
LDEQ concluded:
"In summary, the likelihood of consuming sufficient fish,
solely from the Mississippi River, of a single species, with
any or significant levels of contaminants, and over a long
enough period of time to cause harm is extremely low."
USGS concluded that water quality in the Mississippi River
is improving, mainly because of changes made by chemical manufacturing
industries and improved wastewater treatment by cities and
industries. The USGS report does caution that it only provides
a brief look at the water quality of the river.
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