HYPOTHETICAL CASE
STUDY
Environmental risk
calculation
Accidental spill at Duslo a.s.
- dibuthylphthalate
- xylene
- zineb
TASKS:
 Calculation of PEC
 Use of assessment factors
 Selection of adequate toxicity data (use:
IUCLID)
 Calculation of PNEC
Calculation of Environmental risk
downstream
1
Case Study: Environmental risk calculation for chemicals release due to
a calamity
Purpose: To learn how to calculate environmental concentrations in a river; how to select
toxicity data for risk assessment, how to calculate a PNEC. What is the risk for aquatic
organisms 55 km down stream of Titu, near Bucharest.
HYPOTHETICAL CASE STUDY: Factory DUSLO a.s., located 55 km upstream of
Bucharest, near Titu
Duslo a.s. produces various chemicals including industrial fertilisers, plant production agents,
rubber chemicals, polyvinylacetate dispersions and dispersion glues as well as special
products of organic and inorganic chemistry. Due to a fire in the factory depot 30 kg
dibutylphthalate, 10 kg of xylene and 3 kg of zineb were spilled with the fire extinguishing
water into the river Dambovita.
1.
2.
3.
4.
5.
Calculate the predicted environmental concentration (PEC) at Bucharest
Calculate the predicted No effect Concentration (PNEC)
Calculate the risk coefficient at Bucharest
What are your conclusions based on the calculated risk coefficient.
Take a closer look at the assumptions, are they legitimate for this situation.
1.
Calculation of the predicted environmental concentration:
Dilution of a spilled quantity may be calculated by the equation:
Cmax = 1.36 x 10-4 x M
Cmax
M
=
=
maximum concentration at Bucharest (mg/l)
discharge quantity in kg
This simplification is derived from the Gausian relationship:
Cmax (t) =
M
d
e-kt
-k
t
2.A .D.t
A
D
t
maximum concentration at some distance downstream in (mg/l)
=
discharge quantity in kg
=
dilution between discharge point and some distance downstream
caused by increased water quantity
=
removal
=
first order removal rate (l/day)
=
time (day)
=
volume of water that contains the chemical
=
cross section area of the river (m2)
=
dispersion coefficient (m2/sec)
=
time (sec.)
The following parameter values were used:
k
=
0
(no degradation)
A
=
500 m2
D
=
50
m2/s 432 x 104 m2/day
t
=
0.8
days between Titu and Bucharest
Od

0.45 for Titu to Bucharest
2
The formula used in this dispersion model is based on the following assumptions:
- The substances are highly soluble.
- Decrease in concentration in the water is solely caused by dispersion without degradation,
evaporation and adsorption to floating particles is not taken into account.
- Complete mixing of spills within the water body (river Dambovita).
2
Calculation of the Predicted No Effect Concentration PNEC:
The PNEC can be calculated using toxicity data and by applying an assessment factor. Gather
toxicity data on dibutylphthalate, diphenylamine and zineb in IUCLID.
3
Select the right assessment factor
Select the right assessment factor on the basis of the following scheme:
Available data
At least one short-term L(E)C50 from each of three trophic levels of the
base-set (fish, Daphnia and algae)
One long-term NOEC (either fish or Daphnia)
Two long-term NOECs from species representing two trophic levels
(fish and/or Daphnia and/or algae)
Long-term NOECs from at least three species (normally fish, Daphnia
and algae) representing three trophic levels
Field data or model ecosystems
Assessment
factor
1000
100
50
10
Case by case
PNEC = ratio lowest LC50 or NOEC and an selected assessment factor
4.Calculate the risk coefficient
The environmental risk of a substance can be estimated by the PEC/PNEC coefficient. the
following classification is used:
Classification
PEC/PNEC
Serious risk
>10
Unacceptable risk
1-10
Acceptable risk
0.01-1
Negligible risk
<0.01
3
Acute data for dibutylphthalate are:
Group
Species
Criterion
Result
Algae
Scenedesmus subsp.
Gymnodium breve
EC50 (72 h)
EC50 (96 h)
1.2 mg/l
0.2 mg/l
Invertebrates
Daphnia magna
Artemia salina
Gammarus pseudolim.
Nitocra spinipes
Mysidopsis bahia
EC50 (48 h)
LC50 (24 h)
LC50 (96 h)
LC50 (96 h)
LC50 (96 h)
3.4 mg/l
8.0 mg/l
2.1 mg/l
1.7 mg/l
0.8 mg/l
Fish
Pimephales promelas
Lepomis macrochirus
Ictalurus punctatus
Oncorhynchus mykiss
Perca flavescens
LC50 (96 h)
LC50 (96 h)
LC50 (96 h)
LC50 (96 h)
LC50 (96 h)
0.9 mg/l
0.7 mg/l
0.46 mg/l
1.6 mg/l
0.35 mg/l
Criterion
Result
Other species
Data
quality
-
Chronic data for dibutylphthalate are:
Group
Species
Algae
Selenastrum
capricorn.
Dunaliella parva
NOEC (10 d)
NOEC (8 d)
0.8 mg/l
0.2 mg/l
Invertebrates
Daphnia magna
Gammarus pulex
Dugesia japonica
NOEC (21 d)
NOEC (10 d)
NOEC (7 d)
1.05 mg/l
0.10 mg/l
0.54 mg/l
Fish
Oncorhynchus mykiss
NOEC (99 d)
0.1 mg/l
Other species
-
Data
quality
4
Acute data for zineb are:
Group
Species
Criterion
Result
Data
quality
Criterium
Result
Data
quality
Algae
Invertebrates
Fish
Other species
Chronic data for zineb are:
Group
Species
Algae
Invertebrates
Fish
Other species
5
Acute data for xylene are:
Group
Species
Criterion
Result
Data
quality
Criterium
Result
Data
quality
Algae
Invertebrates
fish
Other species
Chronic data for xylene are
Group
Species
Algae
invertebrates
fish
Other species
6