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Dangerous Substances

The Environment Agency monitors for dangerous substances at a variety of sites within the study area for the purposes of ensuring that the Thames Estuary is compliant with the EC Dangerous Substances Directive.

The EC Dangerous Substances Directive was adopted in 1976 to control pollution caused by certain dangerous substances on the aquatic environment. The Directive established List I substances, which are regarded as particularly dangerous because of their toxicity, persistence and bioaccumulation. Pollution by these substances must be eliminated. Pollution by List II substances regarded as less dangerous but which have a deleterious effect on the aquatic environment must be reduced.

The Dangerous Substances Directive stipulates uniform emission standards (UESs, also known as limit values) and environmental quality standards (EQSs) as approaches for the control of List I substances. For List II substances, all member states are required to establish EQSs on a national level. EQSs for List II substances have been implemented in the UK by the Surface Waters (Dangerous Substances) (Classification) Regulations 1997 and 1998.

The EQSs for selected List I substances are shown below. The table is based on the information presented in “Guidelines for managing water quality impacts within UK European marine sites” (Cole et al., 1999).

Substance**

EQS Type

Marine EQS
(annual average, mg.l-1)

Estuarine EQS***
(annual average, mg.l-1)

Mercury (dissolved)

Annual average

0.3

0.5

Cadmium (dissolved)

Annual average

2.5

5

HCH (Lindane) ****

Annual average

0.02

0.02

Total DDT

Annual average

0.025

0.025

ppDDT

Annual average

0.01

0.01

Pentachorophenol

Annual average

2

2

Aldrin

Annual average

0.01

0.01

Dieldrin

Annual average

0.01

0.01

Endrin

Annual average

0.005

0.005

Isodrin

Annual average

0.005

0.005

Total 'Drins'

Annual average

0.03

0.03

Hexachlorobenzene

Annual average

0.03

0.03

Hexachlorobutadiene

Annual average

0.1

0.1

Carbon tetrachloride

Annual average

12

12

Chloroform

Annual average

12

12

1,2-dichloroethane

Annual average

10

10

Trichloroethyleme

Annual average

10

10

Perchloroethylene

Annual average

10

10

Trichlorobenzene

Annual average

0.4

0.4

*EQS List I taken from www.environment-agency.gov.uk (opens in a new window)
**total concentration (i.e. without filtration) unless specified
*** in the UK, standards for estuaries are the same as for marine EQSs, as established under the Surface Waters (Dangerous Substances) (Classification) Regulations 1989
**** all HCH isomers, including Lindane

EQSs for List II substances have been implemented in the UK by the Surface Waters (Dangerous Substances) (Classification) Regulations 1997 and 1998. The EQSs for selected List II substances are shown below.

 

 

Substance

EQS Type

Marine and Estuarine EQS
(annual average, mg.l-1)

Arsenic (dissolved)

Annual average

25

Chromium (dissolved)

Annual average

15

Copper (dissolved)

Annual average

5

Lead (dissolved)

Annual average

25

Nickel (dissolved)

Annual average

30

Tributyl tin

Maximum concentration

0.002

Zinc (total)

Annual average

40

*The full EQS List II is available on www.environment-agency.gov.uk (opens in a new window)

Water quality monitoring data for the years 1990 to 2000 was provided by the Environment Agency. The Environment Agency undertakes routine monitoring of water quality for dangerous substances at a number of sites along the length of the Thames Estuary (Richmond to North Oaze). These sites are sampled 12 times per annum. Table 6.10 summarises the water quality conditions of all List I substances and selected List II substances. Comments are also provided concerning compliance with the environmental quality standards.

Substance

Mucking (?g.l-1)

Chapman (?g.l-1)

Southend (?g.l-1)

Sea Reach (?g.l-1)

Comments

Mercury (dissolved)

0.018

0.184

0.041

0.04

All data well below EQS, except one 1991 datum at Chapman (3 ?g.l-1)

Cadmium (dissolved)

0.159

0.111

0.078

0.124

All data below EQS and concentrations generally decreasing

HCH (Lindane)

0.006

0.006

0.005

0.006

All data at or below EQS, except one 1990 datum at Sea Reach (0.1?g.l-1)

Total DDT

0.021

0.021

0.019

0.021

All data below EQS since early 1990s

PpDDT

<0.005

<0.005

<0.005

<0.005

All data below EQS since early 1990s, all concentrations at or <0.005 ?g.l-1

Pentachorophenol

0.106

0.109

No data

0.113

All data below EQS and concentrations generally decreasing since early 1990s and stabilising around 0.1?g.l-1 by mid 1990s

Aldrin

0.005

0.005

0.005

0.005

Virtually all data below EQS in early 1990s and all data below EQS since mid 1990s

Dieldrin

0.005

0.005

0.005

0.005

Virtually all data below EQS in early 1990s and all data below EQS since mid 1990s

Endrin

0.005

0.005

0.005

0.005

All data below EQS since mid 1990s

Total 'Drins'

0.02

0.02

0.018

0.019

All data below EQS since early 1990s; sampling at Southend started in 1999

Hexachlorobenzene

0.005

0.005

0.005

0.005

All data well below EQS

Hexachlorobutadiene

0.014

0.015

0.005

0.015

All data well below EQS

Tetrachloromethane

0.264

0.27

No data

0.261

All data well below EQS

Trichloromethane

0.441

0.386

No data

0.386

All data well below EQS

Dichloroethene

1.056

1.019

No data

1.025

All data well below EQS

Trichloroethane

0.29

0.306

No data

0.297

All data well below EQS

Tetrachloroethene

0.259

0.257

No data

0.249

All data well below EQS

Trichlorobenzene

0.045

0.046

No data

0.046

All data well below EQS since early 1990s

Arsenic (dissolved)

2.448

2.159

2.027

1.86

All data well below EQS

Chromium (dissolved)

0.88

0.662

0.285

0.85

All data below EQS with all concentrations <2 ?g.l-1 since early 1990s

Copper (dissolved)

Although in 2000, all concentrations of copper at all sites fell below the EQS level of 5 ?g.l-1, concentrations of dissolved copper at all sites have on average, exceeded the EQS levels. Concentrations dropped in the early 1990s, but a trend toward increasing concentrations occurred from the mid 1990s to the late 1990s, with a reverse in this trend after 1998.

Lead (dissolved)

0.807

0.697

0.342

0.567

All data below EQS, with concentrations falling in early 1990s

Nickel (dissolved)

4.074

2.984

1.775

2.061

Virtually all data below EQS, with concentrations falling in early 1990s

Tributyl tin

0.004

0.003

0.002

0.001

Most data above EQS except for 1999 and 2000, which may reflect sensitivity of analytical equipment since most data for 1999 and 2000 are recorded as "less than" concentrations.

Zinc (total)

Although in 2000, all concentrations of zinc at all sites fell below the EQS level of 40 ?g.l-1, concentrations of total zinc at Mucking, Chapman and Southern have been recorded around the EQS level, whilst at Sea Reach they have mostly fallen below the level. In the last 4 years there is an apparent trend of declining concentrations.

 

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