Regional assessment of status and trends in PBDE concentrations in sediment

Overview

This document describes a regional assessment of the status and trends of PBDE concentrations in sediment in Scottish marine waters. It builds on the 2020 assessment of data from the UK’s Clean Seas Environmental Monitoring Programme conducted by the Clean Safe Seas Evidence Group. In this, assessments of status and trends were made for a large number of PBDE time series, each of a single PBDE at a single monitoring station. The regional assessment synthesises the results of the individual time series to assess status and trends at the biogeographic regional level.

The regional assessment considers the following PBDEs: BDE28, BDE47, BDE66, BDE85, BDE99, BD100, BD153, BD154, BD183, BD209.

The regional assessment synthesises data from monitoring stations that are in estuarine, coastal and offshore waters. The results might therefore differ from regional assessments for Marine Strategy purposes, which exclude estuarine stations.

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 PBDE concentrations is assessed for status if:

• there is at least one year with data in the period 2014 to 2019
• 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 2014 to 2019
• 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. 135 of the 208 PBDE 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 PBDEs. The purple circles are stations where there is a trend assessment for at least one PBDE, 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 PBDE in turn. The colours have the following meaning:

• blue: the mean concentration is significantly (p < 0.05) below the Background Assessment Concentration (BAC)
• green: the mean concentration is significantly (p < 0.05) below the Federal Environmental Quality Guideline (FEQG)
• red: the mean concentration is not signficantly below the FEQG

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 biogeographic region
• the same information presented as proportions
• the number of time series with blue, green or red status in each biogeographic region
• the same information presented as proportions

Stations

BDE28

BDE47

BDE66

BDE85

BDE99

BD100

BD153

BD154

BD183

BD209

Trend summary (numbers)

Number of time series with upwards, downwards or no trend by biogeographic region

region	status	BDE28	BDE47	BDE66	BDE85	BDE99	BD100	BD153	BD154	BD183	BD209	total
Northern North Sea	upward trend	0	0	0	0	0	0	0	0	0	0	0
	no trend	0	5	0	0	0	0	0	0	0	0	5
	downward trend	0	0	0	0	0	0	0	0	0	0	0
Minches & W Scotland	upward trend	0	0	0	0	0	0	0	0	0	0	0
	no trend	0	3	0	0	0	1	0	0	0	0	4
	downward trend	0	0	0	0	0	0	0	0	0	0	0
Irish Sea	upward trend	0	0	0	0	0	0	0	0	0	0	0
	no trend	2	4	2	0	3	2	3	2	2	4	24
	downward trend	0	2	2	1	2	1	2	2	1	0	13
total	upward trend	0	0	0	0	0	0	0	0	0	0	0
	no trend	2	12	2	0	3	3	3	2	2	4	33
	downward trend	0	2	2	1	2	1	2	2	1	0	13

Trend summary (proportions)

Proportion of time series with upwards, downwards or no trend by biogeographic region

region	status	BDE28	BDE47	BDE66	BDE85	BDE99	BD100	BD153	BD154	BD183	BD209	total
Northern North Sea	upward trend		0									0
	no trend		100									100
	downward trend		0									0
Minches & W Scotland	upward trend		0				0					0
	no trend		100				100					100
	downward trend		0				0					0
Irish Sea	upward trend	0	0	0	0	0	0	0	0	0	0	0
	no trend	100	67	50	0	60	67	60	50	67	100	65
	downward trend	0	33	50	100	40	33	40	50	33	0	35
total	upward trend	0	0	0	0	0	0	0	0	0	0	0
	no trend	100	86	50	0	60	75	60	50	67	100	72
	downward trend	0	14	50	100	40	25	40	50	33	0	28

Status summary (numbers)

Number of time series with each status by biogeographic region

region	status	BDE28	BDE47	BDE66	BDE85	BDE99	BD100	BD153	BD154	BD183	BD209	total
Northern North Sea	blue	1	0	1	1	0	0	1	1	3	0	8
	green	9	12	10	2	12	9	10	10	8	3	85
	red	0	0	0	0	0	1	0	0	0	2	3
Minches & W Scotland	blue	0	0	0	0	0	0	0	0	2	0	2
	green	4	5	5	5	5	5	5	5	3	3	45
	red	0	0	0	0	0	0	0	0	0	0	0
Irish Sea	blue	0	0	0	0	0	0	0	0	3	0	3
	green	7	7	7	2	7	7	7	7	4	1	56
	red	0	0	0	0	0	0	0	0	0	6	6
total	blue	1	0	1	1	0	0	1	1	8	0	13
	green	20	24	22	9	24	21	22	22	15	7	186
	red	0	0	0	0	0	1	0	0	0	8	9

Status summary (proportions)

Proportion of time series with each status by biogeographic region

region	status	BDE28	BDE47	BDE66	BDE85	BDE99	BD100	BD153	BD154	BD183	BD209	total
Northern North Sea	blue	10	0	9	33	0	0	9	9	27	0	8
	green	90	100	91	67	100	90	91	91	73	60	89
	red	0	0	0	0	0	10	0	0	0	40	3
Minches & W Scotland	blue	0	0	0	0	0	0	0	0	40	0	4
	green	100	100	100	100	100	100	100	100	60	100	96
	red	0	0	0	0	0	0	0	0	0	0	0
Irish Sea	blue	0	0	0	0	0	0	0	0	43	0	5
	green	100	100	100	100	100	100	100	100	57	14	86
	red	0	0	0	0	0	0	0	0	0	86	9
total	blue	5	0	4	10	0	0	4	4	35	0	6
	green	95	100	96	90	100	95	96	96	65	47	90
	red	0	0	0	0	0	5	0	0	0	53	4

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.

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). Regional trends are then estimated by fitting the following linear mixed model by restricted maximum likelihood:

• response: trend (yearly change in log concentration)
• fixed model: region
• random model: PBDE + region.PBDE + station + trend estimation variation + residual variation

The fixed model means that a trend is estimated for each region. Trends in the different PBDEs are assumed to be broadly similar, because inputs and control measures are likely to affect all PBDEs in a similar way. Each regional trend can thus be interpreted as the common trend in PBDE concentrations in that region (i.e. the trend averaged across all PBDEs).

The random model has five terms:

• PBDE allows for variation in trend between PBDEs common to all regions
• region.PBDE allows for additional variation in trend between PBDEs within regions
• station allows for variation in trend between stations common to all PBDEs
• 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:

• regions 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
• PBDEs with trend information for at least three stations (over all regions): PBDEs are treated as random effects in the meta-anlaysis, so information about trends in one PBDE can be ‘borrowed’ from the trend information in the other PBDEs

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. This ensures that status is always measured on the same scale, even though the assessment concentration might vary between PBDEs and regions. Essentially the same linear mixed model as for trends is then fitted:

• response: status (mean log concentration - log assessment concentration)
• fixed model: region
• random model: PBDE + region.PBDE + station + 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.

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.

Again, the meta-analysis is restricted to regions with at least three status stations with good geographic spread and to PBDEs with status information for at least three stations (over all regions).

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 map shows the stations with parametric trend and status assessments having excluded trend assessments at baseline and impacted stations. The purple circles are stations where there is a trend assessment for at least one PBDE, and the light blue cirles are stations where there are only status assessments.

Regional trends

The first 4 tabs show:

• Regional trends: estimates of the regional trend (averaged over PBDEs) with pointwise 95% confidence intervals
• Regional trends by PBDE: regional trend estimates for each PBDE with pointwise 95% confidence intervals plotted by PBDE
• Regional trends by region: regional trend estimates for each PBDE with pointwise 95% confidence intervals plotted by region
• Individual time series: the trend 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 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 2 tabs show the estimates of the regional trend (averaged over PBDEs) and the regional trend by PBDE

Regional trends

Regional trends by PBDE

Regional trends by region

Individual time series

Estimates by region

This table shows the estimates of the regional trend:

• 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

region	trend	se	lower	upper	% yearly change	%yc lower	%yc upper
Northern North Sea	2.03	3.38	-4.60	8.65	2.05	-4.49	9.04
Minches & W Scotland	-0.08	4.37	-8.65	8.49	-0.08	-8.29	8.86
Irish Sea	-4.94	2.53	-9.89	0.01	-4.82	-9.42	0.01

Estimates by region and PBDE

This table shows the estimates of the regional trend by determinand:

• 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

region	PBDE	trend	se	lower	upper	% yearly change	%yc lower	%yc upper
Northern North Sea	BDE47	2.03	3.38	-4.60	8.65	2.05	-4.49	9.04
Minches & W Scotland	BDE47	-0.08	4.37	-8.65	8.49	-0.08	-8.29	8.86
	BD100	-0.08	4.37	-8.65	8.49	-0.08	-8.29	8.86
Irish Sea	BDE47	-4.94	2.53	-9.89	0.01	-4.82	-9.42	0.01
	BDE99	-4.94	2.53	-9.89	0.01	-4.82	-9.42	0.01
	BD100	-4.94	2.53	-9.89	0.01	-4.82	-9.42	0.01
	BD153	-4.94	2.53	-9.89	0.01	-4.82	-9.42	0.01
	BD209	-4.94	2.53	-9.89	0.01	-4.82	-9.42	0.01

Regional status compared to the Federal Environmental Quality Guideline (FEQG)

The first 4 tabs show:

• Regional status: estimates of the regional status (averaged over PBDEs) with pointwise upper one-sided 95% confidence intervals
• Regional status by PBDE: regional status estimates for each PBDE with pointwise upper one-sided 95% confidence intervals plotted by PBDE
• Regional status by region: regional status estimates for each PBDE with pointwise upper one-sided 95% confidence intervals plotted by region
• 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:

• blue: the mean concentration is significantly (p < 0.05) below the Background Assessment Concentration (BAC)
• green: the mean concentration is significantly (p < 0.05) below the FEQG
• red: the mean concentration is not significantly below the FEQG

Note that to see why some points might be coloured blue, it is necessary to look ahead to the next section, where status is compared to the BAC. Unfortunately, it isn’t easy to present the assessment of status relative to the FEQG with the assessment of status relative to the BAC because the ratio of the BAC to the FEQG can vary between PBDEs and regions.

The final 2 tabs show the estimates of the regional status (averaged over PBDEs) and the regional status trend by PBDE

Regional status

Regional status by PBDE

Regional status by region

Individual time series

Estimates by region

This table shows the estimates of the regional status:

• status: the estimated mean log concentration minus the log FEQG
• se: the corresponding standard error
• upper: the corresponding pointwise upper one-sided 95% confidence limit
• concentration: the estimated mean concentration relative to the FEQG
• conc upper: the corresponding pointwise upper one-sided 95% confidence limit

region	status	se	upper	concentration	conc upper
Northern North Sea	-7.66	1.55	-5.12	0.00	0.01
Minches & W Scotland	-7.54	1.57	-4.97	0.00	0.01
Irish Sea	-6.59	1.53	-4.07	0.00	0.02

Estimates by region and PBDE

This table shows the estimates of the regional trend by determinand:

• status: the estimated mean log concentration minus the log FEQG
• se: the corresponding standard error
• upper: the corresponding pointwise upper one-sided 95% confidence limit
• concentration: the estimated mean concentration relative to the FEQG
• conc upper: the corresponding pointwise upper one-sided 95% confidence limit

region	PBDE	status	se	upper	concentration	conc upper
Northern North Sea	BDE47	-6.52	0.23	-6.14	0.00	0.00
	BDE66	-8.49	0.65	-7.42	0.00	0.00
	BDE99	-2.62	0.33	-2.08	0.07	0.12
	BD153	-11.00	0.63	-9.96	0.00	0.00
	BD154	-11.44	0.72	-10.26	0.00	0.00
	BD183	-14.78	0.74	-13.57	0.00	0.00
	BD209	-1.18	0.31	-0.66	0.31	0.51
Minches & W Scotland	BDE47	-6.29	0.43	-5.58	0.00	0.00
	BDE99	-2.95	0.40	-2.30	0.05	0.10
	BD100	-2.99	0.38	-2.36	0.05	0.09
	BD209	-1.59	0.35	-1.02	0.20	0.36
Irish Sea	BDE28	-8.13	0.35	-7.55	0.00	0.00
	BDE47	-5.79	0.26	-5.36	0.00	0.00
	BDE66	-7.44	0.30	-6.95	0.00	0.00
	BDE99	-1.18	0.27	-0.73	0.31	0.48
	BD100	-3.26	0.33	-2.73	0.04	0.07
	BD153	-9.60	0.29	-9.12	0.00	0.00
	BD154	-10.17	0.31	-9.66	0.00	0.00
	BD183	-13.95	0.37	-13.34	0.00	0.00
	BD209	0.24	0.25	0.65	1.27	1.92

Regional status compared to the Background Assessment Concentration (BAC)

The first 4 tabs show:

• Regional status: estimates of the regional status (averaged over PBDEs) with pointwise upper one-sided 95% confidence intervals
• Regional status by PBDE: regional status estimates for each PBDE with pointwise upper one-sided 95% confidence intervals plotted by PBDE
• Regional status by region: regional status estimates for each PBDE with pointwise upper one-sided 95% confidence intervals plotted by region
• 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:

• blue: the mean concentration is significantly (p < 0.05) below the BAC
• green: the mean concentration is significantly (p < 0.05) below the Federal Environmental Quality Guideline (FEQG)
• red: the mean concentration is not significantly below the FEQG

The final 2 tabs show the estimates of the regional status (averaged over PBDEs) and the regional status trend by PBDE

Regional status

Regional status by PBDE

Regional status by region

Individual time series

Estimates by region

This table shows the estimates of the regional status:

• status: the estimated mean log concentration minus the log BAC
• se: the corresponding standard error
• upper: the corresponding pointwise upper one-sided 95% confidence limit
• concentration: the estimated mean concentration relative to the BAC
• conc upper: the corresponding pointwise upper one-sided 95% confidence limit

region	status	se	upper	concentration	conc upper
Northern North Sea	-0.05	0.86	1.37	0.96	3.95
Minches & W Scotland	0.06	0.90	1.55	1.07	4.69
Irish Sea	1.00	0.83	2.37	2.72	10.68

Estimates by region and PBDE

This table shows the estimates of the regional trend by determinand:

• status: the estimated mean log concentration minus the log BAC
• se: the corresponding standard error
• upper: the corresponding pointwise upper one-sided 95% confidence limit
• concentration: the estimated mean concentration relative to the BAC
• conc upper: the corresponding pointwise upper one-sided 95% confidence limit

region	PBDE	status	se	upper	concentration	conc upper
Northern North Sea	BDE47	1.06	0.23	1.44	2.89	4.21
	BDE66	-0.87	0.65	0.19	0.42	1.21
	BDE99	0.39	0.33	0.93	1.48	2.53
	BD153	-0.98	0.63	0.05	0.38	1.05
	BD154	-1.41	0.71	-0.23	0.24	0.79
	BD183	-2.20	0.73	-1.00	0.11	0.37
	BD209	5.66	0.31	6.17	288.16	480.43
Minches & W Scotland	BDE47	1.28	0.43	1.99	3.61	7.31
	BDE99	0.05	0.40	0.71	1.06	2.03
	BD100	0.02	0.38	0.65	1.02	1.92
	BD209	5.26	0.35	5.83	191.67	339.46
Irish Sea	BDE28	-0.41	0.35	0.16	0.66	1.17
	BDE47	1.78	0.26	2.21	5.95	9.15
	BDE66	0.14	0.30	0.63	1.15	1.89
	BDE99	1.82	0.27	2.27	6.18	9.70
	BD100	-0.25	0.33	0.28	0.78	1.32
	BD153	0.40	0.29	0.88	1.50	2.42
	BD154	-0.17	0.31	0.35	0.84	1.41
	BD183	-1.40	0.37	-0.79	0.25	0.45
	BD209	7.09	0.25	7.50	1202.69	1811.71

PBDE profiles

The profile of concentrations across PBDEs 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: region
• random model: PBDE + region.PBDE + 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 PBDE concentration profiles by region are shown below with pointwise 95% confidence limits. The units are ug/kg dw normalised to 2.5% organic carbon.