Assessment plots and statistical analysis

This report provides details of the assessment of mercury concentrations in plaice muscle at station North Sea (DOGGBK).

• Timeseries metadata. Key information about the timeseries.
• Assessment plot. The fitted trend (solid line) with pointwise 90% confidence bands (grey shaded areas). The trend is plotted on the log scale, with the axis labels back-transformed for ease of interpretation. The points are the annual medians of the individual log concentration measurements, with solid circles denoting uncensored values and < denoting less-than values. The assessment criteria are indicated on the right hand side of the plot and by horizontal dashed lines (if within the range of the data).
• Trend with data. The fitted trend with pointwise 90% confidence bands. The points are the individual concentration measurements, with + denoting uncensored values, d or q denoting values below the limit of detection or quantification and < denoting other less-than values.
• Auxiliary data. The individual concentration measurements with supporting information: mean length of the individuals in the sample; dry weight (%) of the sample; lipid weight (%) of the sample.
• Assessment (related compounds). Assessment plots for all the compounds in the same chemical group measured in plaice muscle at this station.
• Data (related compounds). A scatter plot matrix of all the individual concentration measurements for all the compounds in the same chemical group in plaice muscle at this station.
• Statistical analysis. This tab summarises the fits of models with different amount of smoothing. The final choice is the model with the minimum AICc (with the caveat that a linear model is always preferred to a mean model if there are sufficient years of data). The tab also gives the contrast between the fitted values at the start and end of the timeseries, and over the most recent twenty years. Finally, the tab assesses status by comparing the fitted value at the end of the timeseries to the assessment criteria.

Timeseries metadata

• OSPAR region: 2
• Region: Southern North Sea
• Station code: DOGGBK
• Station name: North Sea (DOGGBK)
• Station latitude: 55.25
• Station longitude: 3.75
• Compartment: biota
• Species latin name: Pleuronectes platessa
• Species common name: plaice
• Tissue: muscle
• Determinand code: HG
• Determinand name: mercury
• Units: μg kg^-1 wet weight
• Extraction: 9 January 2023

Assessment plot

Trend with data

Auxiliary data

Assessments (related compounds)

Data (related compounds)

Statistical analysis

Trend assessment

Analysis of variance

                Df       AIC      AICc  Log lik  Deviance    Chisq Chi df Pr(>Chisq)
mean             1 -5.743991 -2.143991 5.871995 -11.74399       NA     NA         NA
linear           2 -5.348201  2.651799 6.674101 -13.34820 1.604211      1 0.20530749
smooth (df = 2)  3 -6.647175 10.019491 8.323588 -16.64718 3.298974      1 0.06932318

Change in log concentration

              Year start Year end Fit start  Fit end    Change Std error        t  Pr(>|t|)
overall             2014     2021  3.081327 3.362424 0.2810971 0.2082132 1.350044 0.2257031
last 20 years       2014     2021  3.081327 3.362424 0.2810971 0.2082132 1.350044 0.2257031

Status assessment

     Conc fitted Conc ref  Log ratio Std error         t       Pr(>t)
QSsp    28.85905       20 -0.3666914 0.1276684 -2.872218 9.858276e-01
MPC     28.85905      500  2.8521844 0.1276684 22.340566 2.630774e-07

Interpretation

There is no significant temporal trend in the time series (p = 0.2053).

Concentrations at the end of the time series were not significantly below the QSsp (p = 0.9858). Concentrations could therefore have harmed marine life. Concentrations were significantly below the MPC (p < 0.0001), so were unlikely to have harmed human health.