INTRODUCTION TO THE MARINE ENVIRONMENT AND POLLUTION - Marine Pollution: What Everyone Needs to Know - page 17

directly to surface waters. The CWA also provided funding
for municipalities to construct or upgrade sewage treatment
plants. The EPA has implemented pollution control programs
such as setting wastewater standards for industry, and has set
water quality standards for a large number of contaminants
in surface waters. Beyond this, there are additional controls
for waters that are impaired by pollution. Section 303 of the
Clean Water Act authorizes states to identify impaired waters
and calculate limits on the levels of various pollutants that can
enter the impaired water. These limits are called total maxi-
mum daily loads (TMDLs). In 2007, California created a TMDL
for the Los Angeles River in an attempt to reduce the amount
of garbage entering that river, which would in turn reduce the
amount of garbage entering the Pacific Ocean. The CWA will
be discussed further in Chapter 11.
Why are some contaminants that have been banned still
a problem?
National and international laws can regulate or ban chemi-
cals, but “legacy pollution” from persistent contaminants (e.g.,
DDT, PCBs, metals) can remain in sediments for decades after
their use or discharge has been banned, and sediments are
a continuing source of contaminants to organisms. In addi-
tion, many pollutants are still not regulated, and there are
inadequate controls on nonpoint sources. Environmental
regulations and the level of compliance vary widely among
countries. Nevertheless, much has improved in US waters as a
result of the Clean Water Act, which stimulated many munici-
palities to build or upgrade sewage treatment plants.
How extensive and severe is marine pollution around the world?
While humans depend on the oceans for a variety of goods
and services, we have altered and impaired the oceans both
directly and indirectly. A Global Map of Human Impact on Marine