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concentrations in ground-water discharge, the life in the border region. A computerized
process did not completely denitrify the mineral-site database containing information
ground water. As a result, ground-water dis on more than 10,000 sites near the U.S.-
charge still affected the quality of water in the Mexico border has been compiled in the
South Platte River.

USGS Mineral Resources Data System. Each

site record provides the name of the site, its

Peter McMahon location, the commodity mined, the geology has over 10 years of experience as a USGS

of the site, a description of the workings and
hydrologist. His work focuses on the impacts of deposits, and a history of exploration, devel-
biological processes on ground-water quality.

opment, and production at the site. The data-
base includes both metallic and nonmetallic

minerals and materials. Analysis of this infor-
John Karl Böhlke

mation indicates that a wide variety of nonis a research hydrologist whose recent work has

fuel mineral commodities are present in the focused on applications of chemical and isotopic

border region. Mineral resources and minmethods for determining ground-water residence

eral-related issues in the border region that
times and resolving sources, histories, and reactions

will affect the economies of the United States
of anthropogenic contaminants affecting aquifers.
and Mexico include the following.

Mineral-site data are
Many nonmetallic minerals are used for
David Litke

available from the Miner

improving water quality, isolating waste, has worked as a USGS hydrologist in Colorado for

als Information Offices of and mitigating environmental hazards. the last 10 years. His areas of interest include

the U.S. Geological SurImportant resources in the border region surface-water quality, water use, and the use of

vey in digital form or as

include diatomite and zeolites for waste geographic information systems in water studies.

listings, tables, and plots treatment, clays for sealing waste dumps,

and are summarized in and limestone for removing sulfur from

Circular 1098. emissions produced in coal- or oil-fired

power stations. Mineral occurrences and Environmental and

abandoned mine sites may be sources for Resource Studies

acid-mine drainage and elevated levels of

toxic trace elements in soils and ground in the U.S.-Mexico

water.

Mineral materials such as limestone, sand,
Border Region

gravel, and gypsum are widely used in the
border region as construction materials,

especially in rapidly growing urban areas.
atification of the North American Free The border region produces about 18 per-

Trade Agreement (NAFTA) reinforces cent of the world's copper as well as other the need for geoscience data and information metallic commodities, including zinc, lead, in the U.S.-Mexico border region. NAFTA silver, and gold. Metals used in alloy man Area defined as the U.S.-Mexico will accelerate urban, agricultural, and indus ufacture, such as aluminum, cobalt, nickel, border region. trial growth and trade along the border. Such growth and the current and anticipated potential for increased effects on the environment necessitate development of a large,

CALIFORNIA

ARIZONA NEW MEXICO TEXAS coherent geoscience database. Such a data

Santa Fe base is vital to both nations in many disci

Los Angeles Bagdad

Albuquerqu plines, including land-use management,

Phoenix

UNITED STATES urban planning, civil engineering, explora

Nogales tion geology, environmental sciences, envi

Nogales ronmental regulation, resource management,

BAJA CALIFORNIA

Hermosillo MEXICO waste treatment, and industrial mineral sup

NORTE

Chatvana ply. The U.S. Geological Survey (USGS) has

Gulf of

Mexico begun several cooperative projects to compile

Pacific Ocean
existing data and to provide new data related
to these issues.

Data on the distribution and characteris-
tics of mineral sites are essential for
effectively planning industrial and urban
development and for improving the quality of

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on the natural distribution of potentially toxic systems to be compared with anthropogenic activities such as mining.

The establishment and continued construction of a geoscience database, including elements of geology, geochemistry, geophysics, and mineral sites, will allow for effective implementation of NAFTA. The geoscience database forms part of the necessary framework for development of land- and ecosystem-management plans and increased infrastructure, industry, and agriculture in the border region.

For more information on USGS studies in the U.S.-Mexico border region, contact Norman ) Page at:

Telephone: (602) 670–5580

Norman J Page is Scientist-in-Charge of the USGS Center for Inter-American Mineral Resource Investigations,

which conducts cooperative mineral resource investigations, technology transfer and training,

mineral information exchange, and research.

Pesticides in the Atmosphere

and iron, are produced in relatively small
quantities or not at all; thus, for economic
growth, these metals will need to be
imported into the border region.
Minerals such as gypsum, clays, and sulfur
are used to produce fertilizers, animal
feeds, and pesticides.

Another important layer of geoscience information for the U.S.-Mexico border region is a geologic map in digital format. The border region extends across six different geologic provinces from east to west-from the Gulf of Mexico Coastal Plain, across ancient rocks of the stable continental platform and remnants of past volcanic eruptions, to regions where the Earth's crust has been stretched and areas where rocks from ancient ocean environments have been stuck on to the continent. This complex geology complicates the task of producing a coherent map. Geologic maps of the States of Arizona and New Mexico are now available from the USGS in digital format at a scale of 1:1,000,000. The geology of the border region of Texas is being digitized at a scale of 1:500,000, as is the geology of California.

Other current investigations pertinent to the border region include evaluating hydrologic basins that contain aquifers along the border, establishing baseline geochemical information in the larger drainage areas, and examining the dispersion of metals and the natural availability of potentially toxic substances in the region. The San Pedro River Valley in southern Arizona and northern Sonora, Mexico, is composed of several subbasins. A multidisciplinary study to determine the three-dimensional shapes of these subbasins, to describe the relations among the subbasins, and to assess the character and distribution of the sediments filling the basins is underway

This project is an essential first step in assessing the potential for ground-water contamination in subbasin aquifers. Existing geochemical databases are being analyzed and evaluated to provide a geochemical baseline. Some of the samples are being reanalyzed for elements particularly important in identifying potential sites of pollution. These data will also provide a regional hydrogeochemical framework for a large part of southern Arizona and for investigations related to the USGS National Water-Quality Assessment Program in central and southern Arizona. Several investigations are being conducted on the dispersion of metals from mined and unmined ore deposits. Such data will allow the effect of natural mineralization

O

ne of the first issues to be addressed by

(NAWQA) Program National Synthesis is the presence of pesticides in the environment. The goal of the National Synthesis is to use existing data and new data collected during NAWQA studies to assess the status, trends, and cause-and-effect relations for the Nation's highest priority national and regional waterquality issues. About 1.1 billion pounds of pesticides are used each year in the United States to control many different types of weeds, insects, and other pests in a variety of agricultural and nonagricultural settings.

Total agricultural use and the number of different chemicals applied to crops have more than tripled since the early 1960's. Increased use has resulted in increased crop production, lower maintenance costs, and control of public health hazards, but concerns about the potential adverse effects of pesticides on the environment and human health also have grown steadily. The Pesticide National Synthesis begins with detailed reviews of existing information on pesticides in the hydrologic system, including ground and surface waters and the atmosphere. Results for the atmosphere are summarized below.

Pesticides have been recognized as potential atmospheric pollutants since the

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1940's. Early in the history of agricultural pesticide use, off-target drift of applied pesticides was a concern. Long-range movement of pesticides was thought to be minimal, if any, because of their physical and chemical properties (low volatility and low solubility in water). The detection of DDT and other organochlorine compounds in Arctic and Antarctic snow, ice, fish, and mammals changed this notion. The atmosphere is now recognized as a major pathway by which pesticides can be transported and deposited in areas sometimes far removed from their sources.

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which analyses have been made have been detected in at least one atmospheric matrix. Compared with the hundreds of pesticides that have been and are being used, the number and variety of pesticides analyzed from and detected in air and rain are few. These figures do not mean, however, that the majority of pesticides used are not present in the atmosphere. There are several reasons why a particular pesticide has not been found-for example, low use, short atmospheric residence time considering deposition and transformation), the timing of the sampling relative to the timing of use, the predominant atmospheric phase in which it will accumulate relative to the phase being sampled, and, perhaps most important, whether it has been analyzed for in the atmosphere.

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High Atmospheric Concentrations of Pesticides Show Seasonal Trends

Atrazine use in 1988 through the study area (A) and the precipitation-weighted concentrations of atrazine throughout the Midwestern and Northeastern United States from mid-April through mid-July 1990 (B) and 1991 (9).

Pesticide

organochlorine insecticides have been detected in the atmosphere of every State in which they were sought. Organophosphorous insecticides also have been heavily used for decades and are still in high use. As a class, they are not as environmentally persistent as the organochlorine compounds, but they have been detected in most States in which analyses have been made. Triazine herbicides have been in use since the 1960's, but studies in which these compounds are analyzed from the atmosphere did not begin until the late 1970's, when atrazine was found in rain in Maryland. Subsequent studies have detected high levels of triazine herbicides in rain in major corn-producing areas, such as the Midwestern United States. Acetanilide herbicides are frequently used in conjunction with triazine herbicides. Although they are not as environmentally stable as the triazine herbicides, they have been detected in rain at equivalent and even higher concentrations. Many other types of herbicides are used in agriculture, and many of them have been detected in the

Pesticide occurrences in air, rain, and fog

often show seasonal trends; the highest concentrations correspond to local use and planting seasons. In a recent U.S. Geological Survey (USGS) study, samples of rain collected throughout the Midwestern and Northeastern United States were analyzed for a variety of triazine and acetanilide herbicides used in corn and soybean production. The analyses show that the highest concentrations occurred where corn was most intensively grown and corresponded to the spring and summer planting seasons. Observed concentrations for August through March were considerably less. There is a very detailed and strong relation, both spatially and temporally, between atrazine use and concentrations in rain. Pesticides also have been detected at low levels during periods before and after the high-use seasons. These off-season occurrences could be the result of the

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The potential contribution and relative

Land their deposition into surface waters volatilization and wind erosion of previously exposures than humans are, and the U.S. applied material or long-range transport from Environmental Protection Agency and the areas where the planting growing season National Academy of Sciences have set maxistarted earlier. The more persistent pesticides, mum levels of several pesticides for the prosuch as organochlorine insecticides, have

tection of aquatic life. The majority of been detected in the atmosphere at low levels

pesticides in use today, however, do not have throughout the year even though they are no

such established levels. Pesticide concentralonger used in the United States. Another

tions in rain usually are one order of magni-
source of pesticides in our atmosphere is from

tude or more below the human health
long-range transport from areas outside the
United States, such as Mexico, Eastern

standards or maximum contaminant levels
Europe, and Asia, where many organochlo-

for water. There have been several instances, rine insecticides that have been banned in the though, where the concentrations of pestiUnited States are still being used in large cides in rain and fog have exceeded the maxiquantities.

mum contaminant level values for aquatic life

in or near agricultural areas.
Effects of Pesticides on
Water Quality Not Well

Improved Databases Are
Documented

Needed
'he

The extent of pesticides in our atmosphere importance of pesticides from the atmodanes sphere to a body of surface water depend on

are not well known because there is no conas been pesticide levels in atmospheric deposition

sistent nationwide monitoring of pesticides and on how much of the water budget is and their transformation products in atmoderived from surface runoff and direct precip spheric deposition. Existing data on pestiitation. However, very little research has been cides in the atmosphere show that pesticides done on the deposition of pesticides into sur have been found in air, rain, snow, or fog face waters. The most clearly documented throughout the Nation and that most pestieffects of atmospheric pesticides on human

cides studied have been found. The potential bal health and aquatic life, even at the low levels

significance to water quality has not been commonly found in air, rain, snow, and fog,

extensively studied except in the Great Lakes are related to long-lived, environmentally sta

area. The effects on the health of humans and ble organochlorine insecticides that concenfog trate in organisms through biomagnification

aquatic organisms brought about by chronic (food chain accumulation), bioconcentration

exposure to low levels of a wide variety of (environment organism partitioning), or

insecticides, herbicides, and fungicides also both. An example is the organochlorine

are not well known. Water-quality investigainsecticide toxaphene in the Great Lakes tions conducted as part of the NAWQA Proregion. Toxaphene, which is carcinogenic to gram will consider atmospheric deposition as laboratory animals, was never used to any a potentially important source of pesticides, great extent in this area but has been detected particularly during high-use seasons in highin the air, rain, water, sediments, and fish.

use areas, but generally will not conduct The most probable source for this contamina extensive sampling of atmospheric media. tion is long-range atmospheric transport from

The NAWQA Program will work with other the high-use areas in the Southern United

agencies and programs to encourage the States and Mexico.

development of more comprehensive Determining the environmental signifi

monitoring and the study of atmospheric
cance of pesticides in air, rain, snow, and fog

contaminants.
is difficult, and there are no existing national
standards or guidelines for these matrices.

Michael S. Majewski
The only available guidelines are for contam-
inants in terrestrial waters. In addition to

is a research chemist with the
human health concerns, aquatic organisms

Pesticide National Synthesis group of the are often more sensitive to low-level pesticide National Water-Quality Assessment Program.

est od ical

For more information on pesticides in the
atmosphere, contact Michael Majewski at:

Telephone: (916) 979–2609, ext. 345
Internet: majewski@dcascr.wr.

usgs.gov

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