Diffuse Pollution: Pesticides

Question 0

What are the major groups of pesticides?

Answer 0

Organonitrogen
Organohalogen
Organophosphorus
Organosulphur

Herbicides have the largest share of total pesticides = 0.25 M per yr

Question 1

What is the precautionary standard for EU drinking water?

Answer 1

0. 0001mg/L for an individual pesticide - v strict

0. 0005 for total pesticides in water

Question 2

Give an example of a pesticide which remains in gw for long time (begins I)

Answer 2

Isoproturon (even though it’s been phased out has long half life
Has low tendency to absorb to soils thus easily enters water bodies

Question 3

Factors affecting leaching:

Answer 3

<10% reach target pest!

Timing of appl important - March to May sept to nov when evapo losses smaller, greater soil residence time

Question 4

Sorption + degradation -> retention + elimination

Answer 4

Pesticides hydrophobic, high affinity for soil organic matter
But in sorted phase can lead to mobilisation :(

Degrad - can occur by chemical hydrolysis or bacterial oxidation
Designed to have short half life

Question 5

Describe the transport, distribution and transformation processes

Answer 5

Runoff -> deposited in water -> sedimentation -> bioturbation from sed dwelling orgs ->resuspension -> volatization

Changes state from pesticide to metabolite

During sed:
Hydrolysis, redox reactions, biodegradation
Absorption, desorption, diffusion

Question 6

Water company perspective

Answer 6

Anglian water:
4.2 m water customers, 5.6m waste water
Abstractions = 1200ml/ day

Catchments:

50 gw - 226 sources, >500 boreholes
50 sw - 9 reservoirs, direct river abstractions into treatment works, pumping water into impounding reservoirs, gravel pits,

Wensum Abstractions:
Costessey Pits - 17,000ml/a from river Wensum
Attenuation through long residency in storage

Question 7

Pesticide trends - metaldehyde

Answer 7

Exceeded limit in winter ‘08 - mild and wet snails

Need to make alternatives cheaper I.e. SLUXX visible pellets

Question 8

Drinking water treatment

Answer 8

Ion exchange technology for nitrate reduction at gw treatment works

Granular active carbon (GAC) or UV for pesticide red

Anglian region - 20% water treated to reduce nitrate, 55% to remove pesticides

Question 9

GC scanning method

Answer 9

Sample taken after storm event, in Wensum catchment sept dec 2012

19 out of 20 sites had signs of metaldehyde = priority issue!