POPs in Baltic herring

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Scope

Concentrations of PCDD/Fs in fish describes average concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans furans (PCDD/Fs) in fish. Concentrations of sea and freshwater fish species are studied separately.

Definition

Data

Probability distributions of average concentrations of PCDD/Fs (dioxins) in various fish species were extracted from where concentrations of 17 PCDD/F congeners found in different marine and freshwater fish species were collected. Average dioxin concentration was estimated by the arithmetic mean. Because of small number of measurements per species the non-parametric bootstrap procedure was used to create the probability distribution of the arithmetic mean. For fish species with n concentration measurements the procedure employed can be summarized as follows:

1. Draw m samples of size n with replacement from the original sample. These samples are called bootstrap samples.
2. Calculate the sample mean for each of the bootstrap samples.
3. Make the density histogram of bootstrap means.
4. Find a parametric probability density function that matches the histogram best.

As a result a set of parametric distributions was obtained that characterize the uncertainty in the average dioxin concentration in various fish species. The parameters of these distributions are summarized below in results part.

The number of bootstrap replicates m was chosen to be n^n or 2000 (if the numerical evaluation of all n^n samples was impossible).

Unit

pg/g fw WHO-TEQ

Result

Distributions used: Normal(mean,standard deviation) Beta(alfa,beta) Gamma(alfa,beta) Lognormal(mu,sigma)

Fish species	Distribution(parameters)
Baltic Herring	Normal(5.4241,0.7324)
Vendace(inland)	Gamma(0.0487,18.4404)
Vendace(sea)	Normal(0.6021,0.1047)
Whitefish(inland)	Gamma(0.1454,5.7237)
Whitefish(sea)	Lognormal(1.0124,0.1845)
Pike(inland)	Gamma(0.1125,3.8263)
Pike(sea)	Normal(0.9033,0.1425)
Perch(inland)	Normal(0.2492,0.0518)
Perch(sea)	Gamma(0.08,28.908)
Atlantic Salmon	Normal(10.303,1.8453)
Pike-perch(inland)	Beta(9.2899,12.4403)
Pike-perch(sea)	Normal(1.298,0.2839)