Hogy megint felvetem a temat, annak az az oka, hogy most kerult a
kezembe az Environmental Science & Technology legujabb szama, melynek a
vezercikke a szerves szennyezok globalis elterjedesevel, transzportjaval
foglalkozik. / Vol.30, NO. 9, 1996, pp. 390-396., F. Wania & D. Mackay:
Tracking the Distribution of Persistent Organic Pollutants/
A cikkben olvashatok megerositik az altalam korabban allitottakat, azaz:
- a 3.vilagban ma is hasznalnak DDT-t, melyhez export utjan jutnak
- a DDT eljuthat az afrikai orszagokbol Europaba vagy a sarkkorokre
legkori transzport utjan
- a PCB tartalom akkora nagysagrendet er el, melyet korabban F. de
Alencastro tezisebol ideztem es amelyet Barna tulsagosan magasnak velt.
Mivel itt csak reszletek kozolhetok, az olvasoban esetleg olyan kerdesek
merulnek fel, melyek a teljes cikkben megvalaszolasra kerulnek.
> Understanding how persistent organic pollutants (POPs) migrate through the gl
obal environment has become the focus of growing national and international con
cern. Environment ministers from 108 countries concluded a United Nations confe
rence in Washington last November by urging negotiation of a treaty to restrict
the manifacture and use of POPs. ()
POPs are long-lived organic compounds that become concentrated as they
move through the food chain. They have toxic effects on animal
reproduction, development, and immunological function.
() PCBs, DDT. ALTHOUGH THEIR USE IS RESTRICTED OR BANNED IN MANY
DEVELOPED COUNTRIES, POPs ARE STILL MANUFACTURED FOR EXPORT. THEY REMAIN
IN WIDE AND RELATIVELY UNREGULATED USE IN DEVELOPING COUNTRIES. USE OF
SOME COMPOUNDS ACTUALLY IS INCREASING.
THE CONSENSUS AMONG DEVELOPED COUNTRIES FOR RESTRICTIONS ON POPs RESULTS
IN LARGE PART FROM KNOWLEDGE THAT THESE COMPOUNDS CAN MOVE THOUSANDS OF
KILOMETERS FROM THE POINT OF RELEASE. () POPs MAY MIGRATE THROUGH THE
ATMOSPHERE AS GASES AND AEROSOLS AND CONDENSE IN LOW-TEMPERATURE REGIONS
() TRANSIT TOWARD THE NORTH AND SOUTH POLES.
() most POPs are volatile () Warm temperatures favor evaporation from
the Earth's face in tropical and subtropical regions. Cool temperatures
at higher latitudes favor deposition from the atmosphere onto soil and
water.() Natural decomposition reactions slow down in the cold, allowing
POPs to remain intact longer and become more persistent. () Highly
volatile POP compounds tend to remain airborne and migrate faster. Less
volatile POPs will partition into water, snow, ice soil, or vegetation.
The composition of contaminant mixtures thus will vary along a
temperature or latitudinal gradient.
() the migration will take time. There will be a delay in the maximum
concentrations at higher latitudes when compered to areas close to the
sources. () DDT , PEAKED IN THE MOST RECENT LAYERS IN THE HIGH ARCTIC
LAKES. But the peaks occured in older layers (representing accumulation
in the 1960s and 1970s) in more southerly locations. () CLEARLY;
LONG-RANGE TRANSPORT DOES OCCUR.()
HCHs, PREFERENTIALLY DEPOSIT IN POLAR LATITUDES, WHILE DDT DEPOSIT AT
LOWER LATITUDES.Can we define more sharply the characterisics that
undergo global transport(...)?
vapore pressure of the subcooled liquid at 25C (p,p-DDT: Log P:-3,3 Pa)
octanol-air partition coefficient (Log K: 8,7);
temperature of condensation (Tc: +13C).
() BETWEEN 0,01-0,0001 Pa CONDENSE AT TEMPERATURES ABOVE 0 C AND TEND TO
ACCUMULATE IN MID-LATITUDES. () relatively low mobility have a log K of
8-10. () POPs THAT PREFERENTIALLY DEPOSIT IN TEMPERATE AREAS HAVE A Tc
of -10 to +30C. () PCBs with more than five chlorine substitutions TEND
TO REMAIN IN MIDLATITUDES.
() models () and concentrations of POPs in the entire global environment
will be extremely difficult to develop.
() REGIONS OF PAST EMISSION THUS CAN CONTINUE TO ACT AS CONTAMINANT
SOURCES FOR DECADES BECAUSE SLOW RELEASE FROM ACCUMULATED CHEMICAL
RESERVOIRS.
() However, most POPs will fall victim to retention and degradation in
sources areas and never reach polar regions. But concentration in polar
regions can still high. The polar regions are small in area when
compared to the tropical and temperate zones.
() FUTURE GLOBAL POP MODELS MAY ESTIMATE THE % OF A CHEMICAL INTRODUCED
IN CERTAIN REGIONS WHICH WILL EVENTUALLY REACH THE POLAR REGIONS. This %
may be quite small, perhaps only 1 %, BUT COULD BE ECOLOGICALLY
SIGNIFICANT.
|
>> Hat a kerdes inkabb naiv, mint provokativ
>> miert hasznalnak olyan vegyuleteket szerte a vilagban, amirol tudott, >> hog
y karos
> Persze, sokkal szebb meg jobb lenne, ha szepen egeszsegesen halnanak
> ehen.
Nem tudom, hogy vegul mi lesz a dragabb. Kitalaltak vegyszereket,
mellyel noveltek az elelmiszer-termelest. Frankon nagy a szennyezes. A
legkisebb kiserlet is, mely a szennyezok monitoringjahoz, azonositasahoz
kell, rengeteg penzt es faradsagot igenyel. Ha a jovoben merlegre
tehetnenk a dolgokat, attol tartok, nem erte meg az egesz, valahogy el
lett szurva. Gyanitom, hogy az uzletnek, az egyeni haszonnak van itt
nagyobb szerepe. Az ellene fellepo hatas idoben mindig jocskan
eltolodik, ebbol kifolyolag a szennyezes meg egyesek haszna is egyre no.
O.E.
|
