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 |
Estuarine EQS*** |
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 |
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. |