Common Contaminants in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 250

According to ATSDR (2006b), the most toxic dioxin compound
is 2,3,7,8-tetrachlorodibenzo- p -dioxin or TCDD (CAS regis-
try number 1746-01-6). Figure 7.20 shows the basic structure of
TCDD.
Exposure to TCDD may lead to a condition known as chloro-
acne resulting in severe acne-like skin lesions occurring mainly
on the face and upper body. USEPA (2009b) lists many of the
dioxin compounds as either a known or suspected carcinogen.
Dioxin compounds have been shown to bioaccumulate in humans and wildlife and they
behave as teratogens and mutagens (National Research Council 2006).

Cl

Cl

O

Cl

Cl O

FIGURE 7.20
Basic molecular structure of
TCDD.

7.8.3 Fertilizers

Fertilizers are chemical compounds designed to promote plant and fruit growth when
applied (USEPA 2008a). The most common fertilizers are nitrogen (N), phosphorus (P),
and potassium (K). Nitrogen is found primarily in an organic form in soils, but can also
occur as nitrate. Because nitrate is very soluble and mobile, it is transported by surface
water to rivers, lakes, and streams where it can promote algal growth. In many cases the
algal growth is extensive. Nitrate can also contaminate drinking water. Phosphorus occurs
in soil in organic and inorganic forms, but being more soluble than nitrate, can also be
depleted in soil through surface water runoff. Phosphorus can also promote algal growth
in rivers, lakes and streams, because it is a limiting nutrient in fresh water. Potassium (K) in
fertilizers is commonly incorporated as potash—an oxide form of potassium that includes
the compounds potassium chloride, potassium sulfate, potassium nitrate, and potassium
carbonate. The term “potash” comes from the pioneer practice of extracting potassium
carbonate (K 2 CO 3 ) by leaching wood ashes and evaporating the solution in large iron pots.
Fertilizers containing potassium generally do not promote algal growth (USEPA 2008a).
The United States Department of Agriculture (USDA) has tracked fertilizer use in the
United States since 1960. According to the USDA, approximately 140 lb of fertilizer contain-
ing N-P-K are applied each year per acre of land farmed, and this amount has increased
more than 200% since 1960 (USDA 2007).
In urban areas, fertilizers containing N-P-K are common and routinely applied to resi-
dential lawns and golf courses to help maintain green healthy grass and gardens (USEPA
2008a). According to USEPA (2009b), nitrogen, phosphorus, and potassium fertilizers are
not currently known to cause cancer. Exposure to high concentrations may cause nausea
and vomiting.

7.8.4 Cyanide

Cyanide is any chemical compound containing the cyano group—a carbon atom triple-
bonded to a nitrogen atom. This bond is depicted in Figure 7.21. Common cyanide com-
pounds include hydrogen cyanide, potassium cyanide, and sodium cyanide. Certain
bacteria, fungi, and algae can produce cyanide, and cyanide is present in a number of
foods and plants (ATSDR 2006c).
Cyanide compounds occur as gases, liquids, and solids. Inorganic
cyanides are commonly salts of the cyano anion CN − . Organic com-
pounds containing the cyano group are called nitriles. Those com-
pounds that are able to release the cyano group CN − ion are highly
toxic to humans and animals (ATSDR 2006d).

-

C N

FIGURE 7.21
Structure of a cyano
group.