Regional assessment of status and trends in organotin concentrations in sediment
Overview
The 2022 OSPAR CEMP assessment describes the status and trends of contaminant concentrations in biota and sediment at monitoring stations in the OSPAR area. Assessments are made for a large number of time series, each of a single contaminant in a single species and tissue (for biota) at a single monitoring station. This document is one of a series that synthesises the results of the individual time series to assess status and trends at the MIME regional level. In particular, it considers organotin concentrations in sediment, where the organotins are TBSN+, DBSN+, MBSN+, TPSN+, DPSN+, MPSN+. For simplicity, the term ‘region’ is used throughout to describe MIME regions. OSPAR regions are always referred to as such.
The following sections:
- summarise the individual time series results
- describe the methods used to combine the individual time series results to estimate regional status and trends
- present the estimates of regional trends
- present the estimates of regional status
Summary of individual time series results
A time series of organotin concentrations is assessed for status if:
- there is at least one year with data in the period 2015 to 2020
- there are at least three years of data over the whole time series
- a parametric model can be fitted to the data and used to estimate the mean concentration in the final monitoring year (or, occasionally, if a non-parametric test of status is applied)
The conditions are more stringent for trends. Specifically, a time series is assessed for trends if:
- there is at least one year with data in the period 2015 to 2020
- there are at least five years of data over the whole time series
- a parametric model can be fitted to the data and used to estimate the trend in mean concentration
Note that all trend assessments for individual time series and most status assessments are based on the fit of a parametric model. This is important because only the parametric results are passed into the regional assessments in the following sections. 6 of the 128 organotin time series were assessed for status using a non-parametric test.
The first tab below shows all the monitoring stations where there are individual time series assessments of trend or status for organotins. The purple circles are stations where there is a trend assessment for at least one organotin, and the light blue cirles are stations where there are only status assessments.
The next set of tabs show the trend and status assessments for each organotin in turn. The colours have the following meaning:
- green: the mean concentration is significantly (p < 0.05) below the Environmental Quality Standard (EQS)
- red: the mean concentration is not signficantly below the EQS
- black: there are no assessment criteria available
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 final set of tabs give:
- the number of time series with upwards, downwards or no trend in each MIME and OSPAR region
- the same information presented as proportions
- the number of time series with green or red status in each MIME and OSPAR region
- the same information presented as proportions
Note that there are no Background Assessment Concentrations (BACs) and there is only an EQS for TBSN+.
Stations
TBSN+
DBSN+
MBSN+
TPSN+
DPSN+
MPSN+
Trend summary (numbers)
Number of time series with upwards, downwards or no trend by MIME and OSPAR region
| OSPAR region | MIME region | status | TBSN+ | DBSN+ | MBSN+ | TPSN+ | total |
|---|---|---|---|---|---|---|---|
| 2 | Southern North Sea | upward trend | 0 | 0 | 1 | 0 | 1 |
| no trend | 6 | 10 | 25 | 2 | 43 | ||
| downward trend | 25 | 19 | 6 | 0 | 50 | ||
| total | upward trend | 0 | 0 | 1 | 0 | 1 | |
| no trend | 6 | 10 | 25 | 2 | 43 | ||
| downward trend | 25 | 19 | 6 | 0 | 50 | ||
| 3 | Irish and Scottish West Coast | upward trend | 0 | 0 | 0 | 0 | 0 |
| no trend | 1 | 0 | 0 | 0 | 1 | ||
| downward trend | 0 | 0 | 0 | 0 | 0 | ||
| total | upward trend | 0 | 0 | 0 | 0 | 0 | |
| no trend | 1 | 0 | 0 | 0 | 1 | ||
| downward trend | 0 | 0 | 0 | 0 | 0 |
Trend summary (proportions)
Proportion of time series with upwards, downwards or no trend by MIME and OSPAR region
| OSPAR region | MIME region | status | TBSN+ | DBSN+ | MBSN+ | TPSN+ | total |
|---|---|---|---|---|---|---|---|
| 2 | Southern North Sea | upward trend | 0 | 0 | 3 | 0 | 1 |
| no trend | 19 | 34 | 78 | 100 | 46 | ||
| downward trend | 81 | 66 | 19 | 0 | 53 | ||
| total | upward trend | 0 | 0 | 3 | 0 | 1 | |
| no trend | 19 | 34 | 78 | 100 | 46 | ||
| downward trend | 81 | 66 | 19 | 0 | 53 | ||
| 3 | Irish and Scottish West Coast | upward trend | 0 | 0 | |||
| no trend | 100 | 100 | |||||
| downward trend | 0 | 0 | |||||
| total | upward trend | 0 | 0 | ||||
| no trend | 100 | 100 | |||||
| downward trend | 0 | 0 |
Status summary (numbers)
Number of time series with each status by MIME and OSPAR region
| OSPAR region | MIME region | status | TBSN+ |
|---|---|---|---|
| 2 | Southern North Sea | green | 0 |
| red | 36 | ||
| Channel | green | 0 | |
| red | 4 | ||
| total | green | 0 | |
| red | 40 | ||
| 3 | Irish and Scottish West Coast | green | 0 |
| red | 2 | ||
| Irish Sea | green | 0 | |
| red | 5 | ||
| total | green | 0 | |
| red | 7 |
Status summary (proportions)
Proportion of time series with each status by MIME and OSPAR region
| OSPAR region | MIME region | status | TBSN+ |
|---|---|---|---|
| 2 | Southern North Sea | green | 0 |
| red | 100 | ||
| Channel | green | 0 | |
| red | 100 | ||
| total | green | 0 | |
| red | 100 | ||
| 3 | Irish and Scottish West Coast | green | 0 |
| red | 100 | ||
| Irish Sea | green | 0 | |
| red | 100 | ||
| total | green | 0 | |
| red | 100 |
Regional assessment - methods
Tabulating the number of time series with each status category by region provides a quick summary of the individual time series results. However, it does not provide an objective regional assessment of status. Similarly, tabulating the number of time series with an upward or downward trend does not provide an objective regional assessment of trend. This section describes how the individual time series results can by synthesised in a meta-analysis to assess both status and trend at the regional level. In practice there are only sufficient time series to do this for the Southern North Sea.
Trends
For a regional trend assessment, the trend in each time series is summarised by the estimated change in log concentration over the last twenty years (or shorter if the time series doesn’t extend that far back). A regional (Southern North Sea) trend for each organotin is then estimated by fitting the following linear mixed model by restricted maximum likelihood:
- response: trend (yearly change in log concentration)
- fixed model: organotin
- random model: station + trend estimation variation + residual variation
The fixed model means that a separate regional trend is estimated for each organotin. The random model has three terms:
- station allows for variation in trend between stations common to all organotins
- trend estimation variation is the variance of the trend estimates from the individual time series analysis, assumed known and fixed
- residual variation is the variation that cannot be explained by any of the fixed effects or the other random effects
The meta-analysis is restricted to time series from monitoring stations that are classified as ‘representative’ or ‘baseline’ (near pristine conditions or only subject to very diffuse inputs). ‘Impacted’ stations (those close to a point source) are omitted because trends there will likely reflect changes due to the point source and will be ‘unrepresentative’ at the regional level.
The meta-analysis is further restricted to organotins with at least three trend stations with good geographic spread. Three stations is considered the minimum required to provide some sort of evidence base at the regional level.
Status
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 assessment concentration. Essentially the same linear mixed model as for trends is then fitted:
- response: status (mean log concentration - log assessment concentration)
- fixed model: intercept
- random model: status estimation variation + residual variation
where status estimation variation is the variation in the status estimates from the individual time series analysis, assumed known and fixed. The fixed model only includes an intercept since there is an assessment concentration for only one organotin and region.
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.
Presentation
The results of both the trend and status regional assessments are back-transformed for presentation. The estimated regional trend is then interpreted as the percentage yearly change in concentration and the estimated regional status as the ratio of the mean regional concentration to the assessment concentration. To illustrate the latter, 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 tabs show the stations with parametric trend and status assessments for each OSPAR region in turn, having excluded trend assessments at baseline and impacted stations. The purple circles are stations where there is a trend assessment for at least one organotin, and the light blue cirles are stations where there are only status assessments.
The following regions have an insufficient number or time series or spread of stations and are excluded from the regional assessment:
- trend: Irish and Scottish West Coast
- status: Channel, Irish and Scottish West Coast, Irish Sea
OSPAR region 1
OSPAR region 2
OSPAR region 3
OSPAR region 4
Regional trends
The first 2 tabs show:
- Mean trends by organotin: regional (Southern North Sea) trend estimates for each organotin with pointwise 95% confidence intervals
- Individual time series: the trend estimates from the individual time series on which the regional assessment is based. The estimates for determinands with insufficient geographic spread (and excluded from the meta-analysis) are also shown.
The symbols in all these plots have the following interpretation:
- downward triangle: the mean concentration is significantly decreasing (p < 0.05)
- circle: there is no significant change in mean concentration (p > 0.05)
- upward triangle: the mean concentration is significantly increasing (p < 0.05)
The final tab shows the estimates of the regional (Southern North Sea) trend by organotin.
Mean trends by organotin
Individual time series
Estimates by organotin
This table shows the estimates of the mean trend for each organotin:
- trend: the estimated mean yearly change in log concentration across the region (multiplied by 100 for presentation)
- se: the corresponding standard error
- lower, upper: the corresponding pointwise 95% confidence limits
- % yearly change: the estimated mean % yearly change in concentration across the region
- %yc lower, %yc upper: the corresponding pointwise 95% confidence limits
| organotin | trend | se | lower | upper | % yearly change | %yc lower | %yc upper |
|---|---|---|---|---|---|---|---|
| TBSN+ | -10.77 | 0.66 | -12.05 | -9.48 | -10.21 | -11.35 | -9.05 |
| DBSN+ | -7.33 | 0.70 | -8.71 | -5.96 | -7.07 | -8.34 | -5.78 |
| MBSN+ | -0.99 | 0.65 | -2.26 | 0.28 | -0.99 | -2.24 | 0.28 |
Regional status compared to the Environmental Quality Standard (EQS)
The first 2 tabs show:
- Mean status for TBSN+: regional (Southern North Sea) status estimates for TBSN+ 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 EQS
- red: the mean concentration is not significantly below the EQS
The final tab shows the estimate of the regional (Southern North Sea) status in TBSN+.
Mean status by organotin
Individual time series
Estimates by organotin
This table shows the estimates of the mean status for each organotin:
- status: the estimated mean log concentration minus the log EQS
- se: the corresponding standard error
- upper: the corresponding pointwise upper one-sided 95% confidence limit
- concentration: the estimated mean concentration relative to the EQS
- conc upper: the corresponding pointwise upper one-sided 95% confidence limit
| organotin | status | se | upper | concentration | conc upper |
|---|---|---|---|---|---|
| TBSN+ | 1.28 | 0.19 | 1.60 | 3.61 | 4.94 |
Organotin profiles
The profile of concentrations across organotins can sometimes be useful for examining sources, and for comparing concentrations across regions where assessment criteria are not available. Profiles were examined by fitting the following linear mixed model by restricted maximum likelihood:
- response: mean log concentration
- fixed model: organotin
- random model: station + estimation variation + residual variation
where, for each time series, the mean log concentration is the estimated mean log concentration in the final monitoring year and the estimation variance is the variance associated with this estimate.
The estimated organotin concentration profiles for the Southern North Sea are shown below with pointwise 95% confidence limits. The units are ug/kg dw normalised to 2.5% organic carbon.
