History and Risk Assessment of Triazine Herbicides in the Lower Mississippi River

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History and Risk Assessment of Triazine
Herbicides in the Lower Mississippi River
William E. Hartley1 Luann E. White1 James E.
Bollinger2 Arunthavarani Thiyagarajah1 Jeffery M.
Mendler2 William J. George2 1School of Public
Health and Tropical Medicine 2Department of
Pharmacology/Toxicology, School of
Medicine Tulane University New Orleans,
Louisiana
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Table 1. Summary Data on Selected Triazine
Herbicides Atrazine Concentration in
ug/L Date Median 75 95 Max 75-79 0.56
5 1.08 2.47 17.8 80-84 0.44 1.1 3.5 16 85
-89 0.46 0.8 2.4 6.2 90-94 0.46 1.21 3.33
5.6 95-97 0.31 1.1 2.66 4.9 Overall 0.47 1
.1 2.92 17.8 Cyanazine, Unfiltered 92-94
0.151 0.69 5.97 10.2187 95-97 0.124 0.3 0.
86 1.44019 Simazine, Unfiltered 92-94 0.1
2 0.2 0.43 1.39 95-97 0.12 0.27 1.48 3.79

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Table 2. Systemic Toxicity- Drinking Water-
Margin of Exposure (MOE) and Median/MCL
Ratios ATRAZINE Date MOE
MOE 75th MOE 95th MOE Median Median perc
entile percentile Max /MCL 75-79 5
x 10-4 9 x 10-4 2 x 10-3 2 x 10-2
0.19 80-84 4 x 10-4 9 x 10-4 3 x 10-3 1 x
10-2 0.15 85-89 4 x 10-4 7 x 10-4 2 x
10-3 5 x 10-3 0.15 90-94 4 x 10-4 1 x
10-3 3 x 10-3 5 x 10-3 0.15 95-97 3 x
10-4 9 x 10-4 2 x 10-3 4 x 10-3
0.10 Overall 4 x 10-4 9 x 10-4 2 x 10-3 2 x
10-2 0.17
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Table 2. Systemic Toxicity- Drinking Water-
Margin of Exposure (MOE) and Median/MCL
Ratios Date MOE MOE 75th MOE 95th MOE
Median Median percentile percentile Max
/MCL CYANAZINE 92-94 2 x
10-3 1 x 10-2 8 x 10-2 2 x 10-1 NA 95-97 2 x
10-3 4 x 10-3 1 x 10-2 2 x 10-2 NA SIMAZINE
92-94 7 x 10-4 1 x 10-3 3 x 10-3 8 x
10-3 0.03 95-97 7 x 10-4 2 x 10-3 9 x 10-3 2 x
10-2 0.03
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• Purpose
• To characterize the water quality data from
  1975-1998
• on triazine herbicides in the Mississippi River
  south of
• Memphis, TN
• To conduct health and environmental risk
  assessment
• based on temporal trends in the data

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• Introduction
• Triazine herbicides are a group of chemically
  similar herbicides including simazine, propazine,
  prometryn, prometon, cyanazine, ametryn and
  atrazine
• The USEPA in an evaluation of the STORET
  database found atrazine in 4,123 of 10,942
  surface water samples analyzed, representing
  1,659 surface water locations in 31 states. The
  85th percentile value of all non-zero samples was
  2.3 ppb
• Cyanazine was found in 1,708 of 5,297 surface
  water samples
• analyzed, representing 392 surface water
  locations in seven
• states. The 85th percentile value for all
  non-zero samples was
• 4.11 ppb

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USGS, 1992
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USGS (1992)
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USGS (1992)
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• Introduction
• Triazine herbicides - found in Mississippi
  River water reflecting usage during the past 30
  years
• Atrazine concentrations in the Mississippi
  River from 5/1/91 to 3/1/92 were highest during
  May and June, immediately following pesticide
  application and spring rains and dropped below
  detection limits in late summer
• Maximum concentrations of 3.6 ppb atrazine
  in June, 1991, in the Mississippi River near
  Baton Rouge, LA. Larson et al. (1995)

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• Methods
• Tulane University Mississippi River Database
  Project
• Repository of existing water-quality data
  for the Lower Mississippi River, for the area
  just south of Memphis to the receiving waters of
  the Gulf of Mexico
• Three million records of over 800 water
  quality parameters
• Data, collected from academia, government,
  industry and municipal water works, were
  integrated into a relational information system
• Comprehensive source of water-quality
  information available on the lower Mississippi
  River as a single database (Preslan et al., 1997)

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• Methods
• Sources of Triazine Herbicide Data
• Louisiana Department of Environmental
  Quality (LADEQ)
• US Geological Survey (USGS)/ US
  Environmental Protection Agencies Storage and
  Retrieval System (STORET)
• Literature sources (Moody, 1995 Pereira et
  al., 1995 Coupe et al., 1995)
• Jefferson Water Works (JWW) and Orleans
  Water Works (OWW)
• Novartis (formerly Ciba-Geigy Corporation
  Tierney, 1992)
• Academic sources (DeLeon et al., 1986)

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• Data Validation and Assumptions
• Duplicate records removed
• Replaced non-detects with the reported
  detection limit
• Visual inspection of the triazine data
  indicated no apparent outlying points
• Variations in triazine concentrations due to
  sampling location were generally assumed to be
  insignificant throughout the study area - the
  Lower Mississippi River receives very little
  discharge from its surrounding area south of the
  Arkansas River confluence (Sabins, 1997 Wells,
  1980 USACOE, 1976 Everett, 1971)

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• Assumptions
• Similar location assumptions were made with
  regard to source agency - few instances of
  spatial and temporal overlap between interagency
  data were available for comparison
• Exception - atrazine data - relative
  abundance of data allowed for comparison between
  agencies as well as between filtered and
  unfiltered water fractions

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Assumptions Nonparametric statistical
comparisons were conducted on weekly means of
atrazine data, grouped by source agency or water
fraction, to determine whether these data could
be integrated into a single large set. Paired
sets of data from coinciding weeks were analyzed
using the Kruskel-Wallis test (using analysis of
variance on rank-transformed data), with a p
0.05 level of significance (Helsel and Hirsch,
1993). Because no significant differences were
found with respect to sample agency (where
temporal overlap existed) or between filtered and
unfiltered data, all available atrazine data were
combined for the purposes of temporal
characterization and risk analysis.
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• Health and Environmental Assessment Methods
• Risk Assessment National Academy of
  Sciences Guidelines
• Integrated Risk Information System (IRIS)
• Drinking Water SDWA Exposure Assumptions
• Consumption of Fish USEPA Guidance for Fish
  Consumption Advisories
• Ecological Risk Canadian National
  Guidelines

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• Results
• Approximately 5,368 records located on
  triazine herbicides from six existing databases
• Most of the records came from JWW,
  Novartis, and LADEQ
• Approximately two hundred (200) or fewer
  records were available per year up to 1990 with
  typically greater than 500 records available from
  1991 1997

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• Results
• Atrazine, cyanazine and simazine were found
  in significant concentrations
• Propazine, prometryn, prometon, and ametryn
  were at low to trace concentrations
• Based on previously cited application
  patterns, it is expected that atrazine,
  cyanazine, and simazine would be found at
  significant concentrations

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• Results
• Atrazine
• Primarily atrazine records on filtered water
  from 1975- 1993 and atrazine records on
  unfiltered water from 1994-1998
• Consider that atrazine measured in whole and
  filtered water are not significantly different to
  consider analyzing them as separate data sets
• Median atrazine concentrations are higher
  particularly during 1990 and 1993 during which
  there were peak rainfall and/or flood events in
  the upper Mississippi River

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• Results
• Atrazine
• Seasonal analysis of the atrazine levels
  shows expected higher atrazine concentrations in
  June, July and August which is associated with
  peak triazine pesticide usage on crops,
  particularly in the upper Mississippi River
• Lower Mississippi River is highly confined
  by levees and it is unlikely that significant
  loads of atrazine would enter from local
  agriculture except in the event of extreme
  flooding which has not occurred

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• Results
• Cyanazine
• Cyanazine in filtered and unfiltered
  Mississippi River has remained relatively stable
  based on annual averages throughout the study
  period with the exception of 1993 during which
  there was a significant increase probably due to
  flooding of the upper Mississippi River
• Seasonal concentrations of cyanazine were
  typical with significant increases during the
  June to August period and relatively trace levels
  during the remainder of the year

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• Results
• Simazine
• From 1997-1998, simazine shows a pattern of
  increasing concentration beginning in 1992 with
  the most striking increases beginning in 1996
• Causes for this increase in simazine are
  unknown since there are no unusual rainfall
  events or flooding in the upper Mississippi River
  after 1993

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• Results
• Atrazine
• For atrazine, median concentrations and 75th
  and 95th percentile values are similar based on
  analysis of intervals in five year segments with
  the exception of 95th percentile values for the
  1980-84 and 1990-94 periods

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• Results
• The MOE values indicate that for atrazine,
  cyanazine, and simazine, the values fall well
  below MOE 1.0. This indicates that none of the
  chemicals exceed the safe lifetime exposure dose
  (RFD)
• Exposure to maximum values would not exceed
  the safe dose
• Using a worst case additive toxicity model
  for all three chemicals under the assumption of
  similar modes of toxicity, the cumulative MOE or
  Hazard Index (HI) would not exceed 1.0
• The MCL is not exceeded for atrazine and
  simazine. However, some 95th percentile
  concentrations and maximum concentrations do
  exceed the MCL. This poses a legal and regulatory
  issue that may result in an array of remedies
  under the SDWA

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• Health Risk from Fish Consumption
• Exposure assumptions one fish meal per
  week, 70 kg body weight person, and 100
  absorption of atrazine
• Maximum concentration found in a white bass
  fillet was 0.058 mg atrazine per kg fillet
  (LADEQ, 1995)
• There were no significant health risks from
  fish consumption due to atrazine

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• Ecological Risks
• Environment Canada (Government)
  aquatic-life guidelines
• Atrazine 2 ppb
• Cyanazine 2 ppb
• Simazine 10 ppb
• All median atrazine, cyanazine, and simazine
  concentrations were below the Canadian
  guidelines.
• Some 95th percentile and maximum
  concentrations of atrazine and cyanazine exceeded
  the Canadian guidelines

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• Conclusions
• Available historical water quality data from
  1975-1997 for triazine herbicides in the
  Mississippi River south of Memphis, TN were
  characterized in terms of temporal trends and
  with respect to ecological and human health risks
• The most abundant of the triazine compounds
  was atrazine (median concentration 0.47 ppb),
  which also represented the largest dataset,
  followed by cyanazine, and simazine

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• Conclusions
• Extreme rainfall or flooding events in the
  upper Mississippi River Basin were associated
  with increased annual medians for triazine
  herbicides in the lower Mississippi River
• Based on the safe lifetime doses, the
  Maximum Contaminant Levels (MCLs), and aquatic
  life guidelines for atrazine, cyanazine, and
  simazine, no significant health or ecological
  risks from use of Mississippi River water are
  predicted

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