Michael H. Dong

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Environmental Endocrine Disruptors Part III
Persistence and Prevention
Pineal gland
Michael H. Dong MPH, DrPA, PhD
Hypothalamus
Pituitary gland
Thyroid
Parathyroid
gland
gland
Adrenal
Pancreas
glands
Ovaries
Testicles
(women)
(men)
Readings
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05/30/2004, Elk Grove, California, USA
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Course Objectives

• Learn the terms pertaining to a chemicals
  persistence properties, especially those of an
  environmental endocrine disruptor.
• Recognize the science-based criteria and
  assessment models for the determination of
  persistence potential.
• Appreciate the cumulative effects due to a
  disruptors persistence properties.
• Review the processes and strategies for
  prevention of persistent pollution.

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Basics of Persistence (I)

• There are two major aspects or quantities of
  persistence for each chemical substance.
• The first is its intrinsic or chemical
  persistence and the other, its persistence in the
  (overall) environment.
• Environmental persistence is a term used to
  imply a constant quantity or availability of the
  chemical in the environment(s) at issue this
  type of potential thus has greater public health
  importance.

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Basics of Persistence (II)

• Chemical persistence is often expressed in terms
  of a substances degradation half-life.
• The amount of material lost by degradation in a
  medium is determined both by the rate constant
  specific to the reactivity occurring in that
  medium, and by the amount (initially and
  subsequently) present in that medium.
• For chemicals in the environment, their
  degradation half-lives depend not only on their
  physicochemical properties, but also much more on
  the environmental conditions.

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Basics of Persistence (III)

• Environmental persistence is much more dynamic,
  situational, and complex, when compared to
  persistence in a single medium.
• Many substances have properties that allow them
  to partition or dissolve in certain media, and
  even to speciate into a particular, irreversible
  form.
• Environmental persistence thus should be
  evaluated on the basis of degradation rates,
  partitioning, speciation, and availability.

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Long-Range Transport

• An important aspect of environmental persistence
  is its effects towards long-range transport (LRT)
  of the environmental contaminants.
• Through LRT, persistent pesticides and other
  industrial chemicals can be present in remote
  regions such as the Arctic, where these
  substances have never been used.
• The modes of LRT are not limited to
  atmo-spheric, oceanic, or terrestrial, but
  include cyclone activities and animal migration.

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PBT Endocrine Disruptors

• Pollutants that are persistent,
  bioaccumu-lative, and toxic (PBT), of which a
  good number are endocrine disruptors, are
  long-lasting and can build up in the food chain.
• PBTs are of great ecological concern because
  they can induce severe adverse health effects,
  such as endocrine disruption.
• Numerical criteria have been set up to identify
  the persistence and bioaccumulation potentials of
  toxic environmental pollutants.

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Mass Balance Models (I)

• For overall environmental persistence and
  persistence within a single medium, both the
  measurement and the quantity are typically based
  on some mass balance theories.
• Mass balance per se is based on the law of
  conversion of mass it builds on the concept that
  physical or chemical changes do not destroy or
  create matter.
• In practice, the main task of a mass balance
  model is on knowing how much of a material is
  left in the form of interest.

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Mass Balance Models (II)

• Mass balance models (MBMs) appear to offer the
  most convenient means for assessing a pollutants
  persistence in a single medium or in a multimedia
  environment.
• Simple or multimedia MBMs are actually
  mathematical constructs designed to gain an
  understanding of the environmental behavior of
  chemicals.
• In almost all cases, the use of multimedia or
  simple MBMs is limited by the availability of
  data on degradation half-lives.

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Low Levels of PBTs

• For certain types of adverse health effects such
  as endocrine disruption, even low levels of
  persistent and bioaccumulative toxicants (PBTs)
  in the environment collectively are still of
  global concern.
• This is because, by comparison, inducibi-lity of
  environmental endocrine disruption is not
  chemical-selective.
• Yet more importantly, inducibilities of certain
  multiple PBTs for the same adverse effect are
  likely additive, if not synergistic.

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Cumulative Effects (I)

• Concurrent or subsequent exposures to persistent
  and bioaccumulative toxicants, of which many are
  environmental endocrine disruptors, are of global
  concern even when these pollutants are present at
  very low concentrations.
• Synergism or additive effects have been observed
  between steroid hormones between temperature and
  hormone response between weakly estrogenic
  compounds and between pesticides.

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Cumulative Effects (II)

• More recently, additive effects have been
  observed from the combination of a strong
  estrogen 17?-estradiol and a weak estrogen such
  as bisphenol A, nonylphenol, phenyl salicylate,
  butylparaben, or genistein.
• The natural estrogen estradiol is many thousand
  times more estrogenic than any of the weak
  xenoestrogens tested.
• Additive antiandrogenic effects also have been
  observed with the pesticides vinclozolin and
  procymidone.

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Cumulative Effects (III)

• Additive-like effects have been observed from
  multiple thyroid hormone disruptors given to
  rats these disruptors are dioxins, furans, and
  dioxin-likes such as PCBs.
• Other thyroid hormone disruptors, such as
  aldicarb, atrazine, and nitrate, also have been
  found to exert synergistic effects.
• Cumulative effects of this type are highly
  critical in that thyroid functions are important
  for proper growth, metabolism, reproduction,
  mental development, etc.

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Cumulative Effects (IV)

• Studies in various species (rats, salmon, mink,
  chickens) were conducted, which confirmed the
  bioaccumulative effects of concurrent or
  subsequent exposures to pollutants found in the
  Great Lakes fish.
• So was an epidemiology study showing babies born
  with poorer visual recognition from cumulative
  maternal exposure to PCBs mothers of this cohort
  consumed 2 to 3 meals of PCB-contaminated fish
  monthly for 6 years prior to and after pregnancy.

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Time of Exposure

• While exposure to environmental pollutants is
  mainly a function of their availability, time of
  exposure is equally a very crucial factor in the
  induction of endocrine disruption.
• For example, estrogen levels in humans and
  rodents were seen to increase steadily
  through-out the pregnancy period, primarily due
  to a feed-forward mechanism of regulation that
  is, any dose of a xenoestrogen would be additive
  with the endogenous level, due to the lack of
  feed-back control during this period.

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Pollution Prevention (I)

• The potency and toxicity of environmental
  endocrine disruptors (EEDs) are less critical.
• The effects of an EEDs persistence and
  bioaccumulation are much more dynamic, more
  attenuable, and hence more critical.
• One effective method of intervention is to
  divert the pollutant to an environment where its
  degradation half-life can be shortened
  considerably in addition, chemical
  bioaccu-mulation can be intervened by segregation
  of relevant predators in the food chain.

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Pollution Prevention (II)

• All processes and strategies for prevention and
  intervention of environmental pollution revolve
  around the principles of use reduction and source
  elimination.
• Modern methods tend to rely on integrated pest
  management and on chemical treatments for
  elimination and reduction of pollutants.
• A great deal of sewage sludge and other wastes
  also have been reduced considerably in the USA
  through regulatory statues, such as the Clean
  Water Act.

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Pollution Prevention (III)

• Scientific procedures have been adopted
  worldwide for the elimination and the reduction
  of persistent and bioaccumulative toxicants
  (PBTs).
• Numerical criteria are incorporated into
  Canadas Persistence and Bioaccumulation
  Regulations for qualifying pollutants as PBTs.
• Using numerical criteria somewhat more health
  conservative, U.S. EPA has continued updating its
  PBT Profiler for many chemical substances.

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Pollution Prevention (IV)

• International actions on persistent and bio-
  accumulative toxicants (PBTs) require a complex
  process of global compromise.
• The Stockholm Convention in 2001 is a global
  treaty for protection from PBTs. Upon
  ratification, it will ban outright the use of 8
  persistent pesticides and take initiatives to
  reduce the use of 4 non-pesticide PBTs.
• Pollution prevention actually should start with
  an increase in public awareness of the
  environmental levels and sources of PBTs.