rem 610 exercise 7 ecological risk assessment n.
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REM-610 Exercise 7 – Ecological Risk Assessment. March 31, 2010. First Step. The first step of the risk assessment is the problem formulation. Briefly, state the problem including the rationale to conduct a risk assessment. Pollutant is discharged, wildlife exposed  potential for risk

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Presentation Transcript
first step
First Step
  • The first step of the risk assessment is the problem formulation. Briefly, state the problem including the rationale to conduct a risk assessment.
  • Pollutant is discharged, wildlife exposed  potential for risk
  • WQG is exceeded at 0.1 ng/L, concentrations in Bay range from 4.5-26.27 ng/L
  • WQG is the max concentration that should be present to insure the “safety/protection’ of life in the bay
second step
Second Step

The second step is to develop an exposure profile. Start by exploring the reported data. Determine

A) the mean concentration

  • standard mean = 11.77 ng/L
  • geometric mean = 10.61 ng/L

B) the standard deviation of the concentration

  • +/- 5.30 ng/L (standard mean)
  • +/- EXP(.48631) ng/L (geomean)
second step con t
Second Step (con’t)

C) explore the distribution of the data

  • Normal? Skewed? Flat? Etc.
  • in toxicology, typically use the normal distribution & log-normal distribution
third step
Third Step
  • The third step is to develop an ecological profile. Use the data (that you obtained from the literature) in Table 2. To do this, rank the toxicity data and use a rank order model to calculate percentiles. A model that is often used is :
  • R = 100 x n / (N + 1)

  Where R is the rankorder in %, n is the rank order and N is the total number of toxicity data evaluated.

  • You can also make use of the normal probability function of excel, to represent the data by normal probability density function.
fourth step
Fourth Step
  • The fourth step is to conduct the risk analysis. To help you doing this, you can conduct linear regressions for the distributions of exposure concentrations and EC50 data.

-red line – describes a statistical population (of observations)

-the rank of the species tested (not of the real environment)

-black line – e.g. 80% of the chem. Concentration in the water is less than ~log 1.3

-two different populations (one of the lake, other of toxicity tests)

-next, have to look at whether the list of species tested is relevant to the species in our ecological risk assessment

-when setting the limit, should it matter whether a key species is at the bottom?  Have to set the limit to a lower number

  • Write your conclusions for the report that you are going to send to the environmental organization. Try to formulate a concise statement of the “risk” that the ecosystem is facing as a result of the XPS concentrations. Then, explain more thoroughly your assessment of the risk incorporating the merits and limitations of your analysis as well as other ecological principles that should be considered.
conclusions con t
Conclusions (Con’t)
  • It looks like for 90% of the concentration data points collected in Deep Sea Bay, it only causes ~10% of the EC50 effects for various species. There does not seem to be a high risk to the various species living in Deep Sea Bay according to the XPS concentrations collected there even though the XPS concentrations are well above the water quality guideline of 0.1 ng/L.

Merits: Takes into account many data points from the measurements around the lake and also from various species’ EC50.


  • EC50 values are obtained on a short-term basis (48 hours – 14 days), but the animals living in Deep Sea Bay may be exposed to the chemical on a long-term basis and this doesn’t take that into account, perhaps bioaccumulation?
  • There are only 6 data points for the EC50 values, and 1 point for each species. There is not enough data. It would be better if there are more data points for each species.