Regional assessment of status against human health thresholds in PCB concentrations in biota
Overview
This document provides additional regional assessments of the status of PCB concentrations in biota based on human health rather than environmental thresholds. The regional assessments are part of the 2020 assessment of CSEMP data and concern the PCB SCB6 which is compared against the Maximum Permissible Concentration (MPC). Methodological details are only described briefly: further information can be found in the resource biota_regional_assessment_pcbs.html.
Summary of individual time series results
This section summarises the individual time series assessments of trend and status for SCB6. This is the only place where trends are presented as the focus of this document is on status relative to the MPC.
The first tab show the trend and status assessments for SCB6. The colours have the following meaning:
- green: the mean concentration is significantly (p < 0.05) below the MPC
- red: the mean concentration is not signficantly below the MPC
And the shapes have the following meaning:
- downward triangle: the mean concentration is significantly decreasing (p < 0.05)
- circle: there is no significant change in mean concentration (p > 0.05) or there are too few years to test for trends
- upward triangle: the mean concentration is significantly increasing (p < 0.05)
The second set of tabs give:
- the number of time series with upwards, downwards or no trend in each biogeographic region and MS sub-region
- the same information presented as proportions
- the number of time series with green or red status in each biogeographic region and MS sub-region
- the same information presented as proportions
SCB6
Trend summary (numbers)
Number of time series with upwards, downwards or no trend by biogeographic region and MS sub-region
| MS sub-region | biogeographic region | status | SCB6 |
|---|---|---|---|
| Greater North Sea | Northern North Sea | upward trend | 0 |
| no trend | 8 | ||
| downward trend | 3 | ||
| Southern North Sea | upward trend | 0 | |
| no trend | 6 | ||
| downward trend | 3 | ||
| E Channel | upward trend | 0 | |
| no trend | 2 | ||
| downward trend | 0 | ||
| total | upward trend | 0 | |
| no trend | 16 | ||
| downward trend | 6 | ||
| Celtic Seas | Minches & W Scotland | upward trend | 0 |
| no trend | 0 | ||
| downward trend | 4 | ||
| Irish Sea | upward trend | 0 | |
| no trend | 5 | ||
| downward trend | 11 | ||
| W Channel & Celtic Sea | upward trend | 0 | |
| no trend | 2 | ||
| downward trend | 1 | ||
| total | upward trend | 0 | |
| no trend | 7 | ||
| downward trend | 16 |
Trend summary (proportions)
Proportion of time series with upwards, downwards or no trend by biogeographic region and MS sub-region
| MS sub-region | biogeographic region | status | SCB6 |
|---|---|---|---|
| Greater North Sea | Northern North Sea | upward trend | 0 |
| no trend | 73 | ||
| downward trend | 27 | ||
| Southern North Sea | upward trend | 0 | |
| no trend | 67 | ||
| downward trend | 33 | ||
| E Channel | upward trend | 0 | |
| no trend | 100 | ||
| downward trend | 0 | ||
| total | upward trend | 0 | |
| no trend | 73 | ||
| downward trend | 27 | ||
| Celtic Seas | Minches & W Scotland | upward trend | 0 |
| no trend | 0 | ||
| downward trend | 100 | ||
| Irish Sea | upward trend | 0 | |
| no trend | 31 | ||
| downward trend | 69 | ||
| W Channel & Celtic Sea | upward trend | 0 | |
| no trend | 67 | ||
| downward trend | 33 | ||
| total | upward trend | 0 | |
| no trend | 30 | ||
| downward trend | 70 |
Status summary (numbers)
Number of time series with each status by biogeographic region and MS sub-region
| MS sub-region | biogeographic region | status | SCB6 |
|---|---|---|---|
| Greater North Sea | Northern North Sea | green | 18 |
| red | 0 | ||
| Southern North Sea | green | 10 | |
| red | 0 | ||
| E Channel | green | 4 | |
| red | 0 | ||
| total | green | 32 | |
| red | 0 | ||
| Celtic Seas | Minches & W Scotland | green | 4 |
| red | 0 | ||
| Irish Sea | green | 19 | |
| red | 2 | ||
| W Channel & Celtic Sea | green | 3 | |
| red | 0 | ||
| total | green | 26 | |
| red | 2 |
Status summary (proportions)
Proportion of time series with each status by biogeographic region and MS sub-region
| MS sub-region | biogeographic region | status | SCB6 |
|---|---|---|---|
| Greater North Sea | Northern North Sea | green | 100 |
| red | 0 | ||
| Southern North Sea | green | 100 | |
| red | 0 | ||
| E Channel | green | 100 | |
| red | 0 | ||
| total | green | 100 | |
| red | 0 | ||
| Celtic Seas | Minches & W Scotland | green | 100 |
| red | 0 | ||
| Irish Sea | green | 90 | |
| red | 10 | ||
| W Channel & Celtic Sea | green | 100 | |
| red | 0 | ||
| total | green | 93 | |
| red | 7 |
Regional assessment - methods
For a regional status assessment, the status of each time series is summarised by the difference between the estimated mean log concentration in the final monitoring year and the log MPC. The regional status for SCB6 is then estimated by fitting the following linear mixed model by restricted maximum likelihood:
- response: status (mean log concentration - log MPC)
- fixed model: region
- random model: station + status estimation variation + residual variation
There are no restrictions on the time series used in the status meta-analysis based on the classification of the monitoring station; time series from baseline, representative and impacted stations are all included. However, the few time series with a non-parametric assessment of status must be excluded, because there is no summary measure of status to use in the mixed model.
The meta-analysis is restricted to regions with at least three status stations with good geographic spread.
The results of the status regional assessments are back-transformed for presentation. The estimated regional status is then interpreted as the ratio of the mean regional concentration to the assessment concentration. For example, a value of 1 indicates that the mean regional concentration is equal to the assessment concentration; a value of 0.5 indicates that it is half the assessment concentration, and a value of 2 indicates that it is twice the assessment concentration.
Regional assessment - availability of time series
This section provides more detail on the number and geographic spread of the time series available for the meta-analyses. The map shows the stations with parametric status assessments `
Regional status compared to the Maximum Permissible Concentration (MPC)
The first 2 tabs show:
- Regional status: estimates of the regional status for SCB6 with pointwise upper one-sided 95% confidence intervals
- Individual time series: the status estimates from the individual time series on which the regional assessment is based. The estimates for regions with insufficient geographic spread (and excluded from the meta-analysis) are also shown.
The symbols in all the plots have the following interpretation:
- green: the mean concentration is significantly (p < 0.05) below the MPC
- red: the mean concentration is not significantly below the MPC
The final tab shows the estimates of the regional status in SCB6.
Regional status
Individual time series
Estimates by region
This table shows the estimates of the regional status:
- status: the estimated mean log concentration minus the log MPC
- se: the corresponding standard error
- upper: the corresponding pointwise upper one-sided 95% confidence limit
- concentration: the estimated mean concentration relative to the MPC
- conc upper: the corresponding pointwise upper one-sided 95% confidence limit
| biogeographic region | status | se | upper | concentration | conc upper |
|---|---|---|---|---|---|
| Northern North Sea | -2.26 | 0.23 | -1.88 | 0.10 | 0.15 |
| Southern North Sea | -2.09 | 0.28 | -1.63 | 0.12 | 0.20 |
| E Channel | -2.44 | 0.45 | -1.70 | 0.09 | 0.18 |
| Minches & W Scotland | -4.12 | 0.48 | -3.34 | 0.02 | 0.04 |
| Irish Sea | -1.79 | 0.20 | -1.45 | 0.17 | 0.23 |
| W Channel & Celtic Sea | -1.94 | 0.50 | -1.13 | 0.14 | 0.32 |