Elaboración de un palo de lluvia

Water quality standards for organotins (µg l-1) are shown below (table 13).

Table 13. Water Quality Standards for organotins

Tributyltin TBT 0.002µg l-1 _MT

Triphenyltin TPT (and its derivatives)

0.008 µg l-1 _MT

M= Maximum T= Total concentration (ie without filtration)

The EQS for TBT of 2 ng l-1, as discussed in the previous section, is often exceeded in the Fal by a considerable margin. Acute effects in a range of species such as algae, molluscs, crustaceans and fish are reported to occur at dissolved concentrations of the order of 1 µg l-1 which is above the range usually encountered. However chronic effects are known to occur in several species down to 1ng l-1 and are clearly of significance in the Fal cSAC.

TBT. Of the 644 results for TBT (1996-2001), 244 were below the detection limits, which for tidal waters were generally set at 20ng l-1 or below. However in the vicinity of outfalls and discharges, detection limits were variable and set at up to <388ng l-1, and exceptionally >15000ng l-1 TBT (Falmouth Docks outfall). For the purposes of this brief summary, only positive results are included, and tidal waters, and STW outfall/discharge waters are considered separately. (A more thorough review of EA TBT data is provided in Harris, 2001)

Tidal waters: Considering all positive results, mean and median values were 23 and 14ng l-1 respectively (n=177) with maximum values of 247 and 200ng l-1 occurring in the Penryn River at Islington Quay and the river Fal (mid-channel). Figure 27 summarises the data for the tidal waters of the Fal. Values are generally very high with maximum values exceeding the EQS at all but two sites. There are no significant temporal trends in the data to suggest a reduction of TBT levels in the water column.

Min-Max 25%-75% Median value TBT in tidal waters of the Fal Estuary

Data source:EA TBT ng L -20 40 100 160 220 280

Penryn Fal Marina

Penryn Islington Qua

Penryn Fal Docks _{Percuil opp Percuil} Rest Crk Mouth Black Rock Buoy Ki

ng Harry Ferry

Fal mid-channel

Fal Mylor Yacht Club

Fal mid-point Fal Vilt Buoy

Figure 27. TBT (ng l-1) in the tidal waters of the Fal Estuary

Outfall/discharge waters: Positive results available for TBT in discharges (1996- 2001) are summarised in figure 28. Mean and median values for all discharge/outfall data are 2462 and 283ng l-1 respectively, with maximum values for TBT of 27.7 and 9.4µg l-1 occurring in Falmouth Docks combined outfall and surface waters. The outfall at Falmouth Docks stands out as the principal source of TBT in the area, with mean and median concentrations of 7240 and 6007ng l-1 _{respectively. Nevertheless,}

maximum TBT concentrations at all sites are far in excess of EQS values and no doubt contribute significantly to the TBT problem in the area. Again, there are no temporal trends in the data to date, to indicate a reduction of TBT concentrations in discharges and sewage treatment effluent entering the Fal Estuary. However recent washwater inputs of TBT from the Docks are now anticipated to be lower following the commissioning of an active-carbon treatment plant (EA personal communication).

Min-Max 25%-75% Median value TBT ng L -2000 2000 6000 10000 14000 18000 22000 26000 30000 Tank far m dischar ge Fal sur face boil

Docks combined outfa

Docks N. whar

f

Docks outfall sur

fac

Fal STW (UV)

Fal STW sur

face boil

Figure 28. TBT (ng l-1) in discharges entering the Fal Estuary (1996-2001)

TPT. Triphenyltin is also used in antifouling paints, though to a lesser degree than TBT. Data available for TPT monitoring in the Fal are for the period 1993-1997 and is mostly restricted to sites in the immediate vicinity of Falmouth STW and dockyard discharges. Of the 167 results available, 136 are denoted as below detection limits, however those ‘less than’ values range from 11-411ng l-1 and all exceed the EQS of 8ng l-1. Positive results are available for two sites primarily (Falmouth Docks outfall and surface waters at Falmouth Dockyard outfall) and are in the range 6-216ng l-1. With one exception, all positive results exceed the EQS value (mean and median values 45 and 30ng l-1_{). Concentrations in this range would be expected to contribute}

significantly to the overall TPT burden in the estuary. In the absence of more recent data we cannot comment on current levels of TPT, however there was no indication in the available data to suggest that levels in discharges were reducing therefore we may conclude that TPT, like TBT is an ongoing water quality problem in the area.

Tetraphenyltin: Although tetraphenyltin is not listed as a ‘list II’ substance, up-to- date monitoring information is available in the database for non-discharge sites in the Fal Estuary, therefore a brief summary is warranted: Of the 559 results for tetraphenyltin (1996-2001) 515 are denoted as above or below detection limits. Positive results for tetraphenyltin in STW effluent and discharges in the Falmouth area are again very high (mean and median 398 and 38ng l-1). However, results for tetraphenyltin in waters away from discharges and outfalls are largely reported as less than 7ng l-1 or less than 1ng l-1.

No data are available for TBT, or TPT concentrations in the Helford river therefore we cannot comment on Helford waters with regard to organotins. This represents a substantial gap in our knowledge of the water quality in the cSAC. The estuary has

approximately 500 deepwater and intertidal moorings, and there is a boatyard at the head of the estuary at Gweek. Around the time of the 1987 ban on use of TBT-based antifouling paints, Covey and Hocking (1987) noted a ‘dramatic decline in numbers of dogwhelk Nucella lapillus due to TBT’ and recorded that Nucella populations were present only at outer headlands Nare Point and Rosemullion Head. As noted in the previous section, TBT is readily adsorbed onto particles and may persist in the sediment where there is potential for re-release into the water column.