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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