BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS
FACULTY OF CHEMICAL AND
BIOCHEMICAL ENGINEERING
DEPARTMENT OF CHEMICAL AND
ENVIRONMENTAL PROCESS
ENGINEERING
PESTICIDES
Dr. Bajnóczy Gábor
Tonkó Csilla
PESTICIDES
Why they are necessary?
Insects, rodents, weeds, fungi are competitors in human feeding.
Used chemical matters against them : pesticides
Success is not exclusive ↔ significant environmental damage
Groups of pesticides (by effects):
-Insecticides
-Fungicides
-Herbicides
-Rodenticides
-Molluscicides
-Akaricides
-Nematocides
TYPES OF PESTICIDES (BY CHEMICAL ASPECT)
Chlorinated hydrocarbons
(insecticides)
Carbamates
(insecticides)
Limited utilization
Aim: substitution of
organophosphates
Chlorophenoxy acides
(weed killers)
Pyrethroids
(insecticides)
Significant amount
Aim: production of natural
pesticides
Organophosphates
(insecticides)
Aim: substitution of chlorinated
hydrocarbons
Other heterocycle compounds
MOST IMPORTANT PROPERTIES OF PESTICIDES
(ENVIRONMENTAL ASPECTS)
Lifetime of pesticides:
The lifetime of a pesticide is the time after which 95 % efficiency reduction
occurs at ambient conditions
Fast degradable agents: degradation 1 – 12 weeks
Moderately fast degradable agents: degradation 1 – 18 months
Slowly degradable agents: degradation more than 2 years
Disadvantage of slow degradation:
a./ accumulation in food chain
b./ development of resistance
New type of pesticides: fast degradation is advantageous
Degradation types: biological, photochemical, water hydrolyses
TOXIC EFFECT TO LIVING ORGANISMS
Most commonly used: LD50 (lethal dose)
• amount of material [mg / bodymass kg] causes 50% death in the
population examined during the test period (e.g. 24 hours).
LD50 value depend on the way of poison acces: oral or dermal.
Poison category
Strong poison
Poison
Weak poison
Non-toxic
acute, oral LD50
[mg/body mass kg]
< 50
50 – 500
500 – 5000
> 5000
measured in rats
TOXIC EFFECT TO LIVING ORGANISMS
toxic effect of pesticide to small mammals (rat)
oral LD50
*[mg / bm kg]
DDT
malathion
200 – 400
100 – 200
dichlorophosphate
carbaryl
10 – 80
300 – 2000
250 - 1500
Chlorinated hydrocarbon
Organophosphates
dermal LD50
*[mg / bm kg]
2000 –
3000
Carbamates
pyrethroids
*[mg / bm kg] = [mg / bodymass kg]
Pyrethroids: mammals –> good resistance
fishes –> LD50 in 1,8 μg/ water dm3 96 hours
100 – 200
CHLORINATED HYDROCARBONS
The best know: DDT
Catch in membrane pore of nerve tissue →
inhibition of nerve transfer.
Non-chemical effect.
Stereo chemically similar compounds: DDT effect
is observed
Non-polar – solubility is negligible in water (this was thought)
Large amount of DDT has been sprayed.
http://www.whale.to/vaccines/ddt_spraying.html
http://www.life.com/animals-pictures/50531439/mobile-ddt-spraying-machine-in-action
DDT ACCUMULATION IN FOOD CHAIN
birds
freshwater fish
water plants
sea fish
plankton
invertebrates
fresh water
sea water
DDT conc. of sea water = 1 ppb → DDT conc. of oyster: DDT ~ 70 ppm
Degree of enrichment: 70 000 !!
EFFECT OF DDT ACCUMULATION
Increased DDT level increases the amount of cytochrome P-450 enzyme.
The non selective oxidizing enzyme oxidizes not only the DDT, but other
Important hormones e.g. estradiol (responsible of the calcium intake into
the egg shell.
?
low calcium content of egg shell: eggs break under penguin
fast degradable agent: biological accumulation has less opportunity
FORMATION OF RESISTANCE I.
If the organism contested gets less than the lethal dose it has opportunity
to learn how organization protect themselves against the effects of the pesticide.
This ability developed is heritable.
Due to the apolar skin only apolar pesticides are able to penetrate the skin.
non-polar
pesticide
enzyme
polar
molecule
fast,
easy
excreted by urine
In case of rapidly degrade pesticides the time is short to create the defense!
FORMATION OF RESISTANCE II.
In case of a significant number of individuals (millions)
due to the biological diversification there are existing
individuals which already have a deactivating enzyme
that can disarm the pesticide applied.
The capability of existing defence is heritable.
In this case, the pesticide lifetime
life is irrelevant.
FORMATION OF RESISTANCE III.
disarming options of non-polar DDT molecule in wildlife
stable
mosquito
fly
mammals
fruit fly
toxic, non-polar molecule
non toxic, polar molecule
urine
CHLORINATED HYDROCARBONS TODAY
Forbidden or significantly limited: on the northern hemisphere of the Earth
In some developing countries, due to the large number of diseases (malaria, yellow
fever) and the food production threatened by pests now the ban could not be done.
The crop contaminated by chlorinated hydrocarbons, once it enters the EU
moves freely in the member states.
opportunities in Africa
premature death
(famine or disease)
longer life but
chronic effect of
chlorinated hydrocarbons
http://www.eoearth.org/article/Chemical_use_in_Africa:_opportunities_and_risks
ORGANOPHOSPHATES
Developed instead of chlorinated hydrocarbons
faster degradation → difficult to develop resistance and accumulation
Y
X and Y : sulfur or oxygen
R
P
R’
X
Z
R, R’ : hydrocarbon, oxygen content is possible
Z : complex organic group
The acetylcholine plays a significant role in the nerve transfer among the nerve cells.
After the job is finished, the enzyme acetylcholin is decayed by acetylcholine esterase.
Organophosphates block the acetylcholine esterase.
Acute toxicity to humans and animals as well !
The toxic potency can be influenced by the quality of the chemical groups!
Freely available or official authorization is necessary for purchase.
ORGANOPHOSPHATES
Ester bond degrades rapidly under environmental conditions
Disadvantage: frequent use is necessary
Hydrolysis and conversion of parathion
S
(RO) 2
P O
(RO)
2
NO
oxygen (air)
water
(RO) 2
P O
(RO) 2
P
OH
HO
NO
(RO)
2
2
non-toxic
biological
decay
O
bacterial
HO
P
2
NO 2
toxic
hydrolysis → non-toxic compounds
non-toxic
transformation
NH
HO
HO
over time, transformed into
another toxic substance
O
S
(RO)
2
OH
conjugation to humic acids
2
CARBAMATES
Developed to substitute organophophates
Insecticide effect, less toxic to mammals, fast degradable agent
bacterial
decay
light
water
CARBAMATES
degradation of carbamates → hydroxy naphthalenes
incorporation
into the humic
acid content
of the soil
STRUCTURE OF HUMIC ACID
PYRETHROIDS
Any of several synthetic compounds similar to pyrethrin, used as an insecticide.
Pyrethrin: multicomponent insecticid effect agent from powdered flower of Dalma flowers
(Chrysanthemum cinerariaefolium)
Disadvantage: easy deagradation in visible light
Advantage: natural, household utilisation, non-toxic effect to mammals.
Synthetic pyrethroids: pyrethrin base compounds:
permethrin, cypermethrin, deltamethrin etc.
effect: long-term, slightly toxic to mammals, toxic to bees and fishes
( 2.0 μg/dm3, lethal effect on carp after 96 hours)
Permethrin
THIRD GENERATION INSECTICIDES
First generation insecticides: agents before World War II.
- toxic inorganic compounds
(lead-arsenate, mercury and lead-containing compounds)
- toxic organic compounds, e.g. nicotine, pyrethrin
Second generation insecticides:
- synthetic insecticides (chlorinated hydrocarbons,
organophosphates, carbamates, pyrethroids)
Third generation insecticides:
- attractive materials (detection of swarming period → spraying in right time →
decreasing the unnecessary amount of pesticide)
- pheromones (sex pheromones – can disturb reproduction)
- viruses (specifically killing organisms)
- hormones (effect on insects evolution,
effective only in a particular stage of life)
- sterilization (inhibition of reproduction e.g. with irradiation)
Herbicides
Chlorophenoxy acids (amine salts and esters)
2,4 - dichlorophenoxi acetic acid (2,4-D)
2,4,5 - trichlorophenoxi acetic acid (2,4,5-T)
Hormonal effect agent against dicotyledonous weeds
Forced fast growing → not enough nutrient → decay of plant
Pesticides used in the largest quantity in the world.
Degradation is a few weeks in soil.
Low toxic effect to invertebrates, vertebrates, but the chronic effect is not
clearly demonstrated.
DEGRADATION OF CHLOROPHENOXY ACIDS
IN THE ENVIRONMENT
Microbiological degradation
Dispersion of large amount of chlorophenoxy acids (Vietnam War, Agent Orange)
terratogen effect to population
Cause: by-product: dioxine (in ppm) range