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| Investigation of the metabolic activity of organisms in soil and water can be assessed by reference to phosphatase activity. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Phosphatases are enzymes that catalyse orthophosphate release from organic phosphomonoesters. Jones (1972) proposed that relative phosphatase activity could be used as an indicator of biomass, and comparative studies (e.g. Matavulj, Gajin et al., 1989) confirmed that water enzymatic activity serves as a useful indicator of surface water eutrophication. Most micro-organisms synthesise phosphatases, thus a Phosphatase Activity Index (PAI) can reflect the extent of biomass in microbial habitats over periods of time. The hypothesis adopted here is that electric fields from high voltage power lines may influence the extent of microbial growth, and that this can be measured by the PAI compared with duration of exposure. It is accepted that phosphorus is the most common factor limiting growth. Changes in microbial habitats can therefore be followed by reference to phosphomonester hydrolases (PMEH). PMEHs are a group of non specific enzymes which hydrolyse organic phosphates (and some inorganic condensed phosphates). Reaction can have an optimal pH of about 5 (acid phosphatases) 7.0 (neutral phosphatases) and about 9.0 (alkaline phosphatases). Inhibition of these enzymes and repression of their synthesis (especially alkaline phosphatases) induced by inorganic phosphates (Pi) are of great ecological significance. Average phosphatase activity, that is the PAI, represents the mean value of potential acticities of acid, neutral and alkaline phosphatases maximally expressed at adjusted pH for enzyme group examined.In consequence the pH value of the medium of interest does not affect the total phosphatase activity level. PAI is expressed as mmol of para-nitrophenylphoshate ("pNP/s/dm3")as released from pNP as a result of the enzymatic activity of the sample. It is generally calculated using the molar extinction coefficient (see Flint, 1974) TESTING PHOSPHATASE ACTIVITY UNDER HV POWER LINES Phosphatase activity was tested for bacteria (Bacillus sp.). Three controls were used (i.e. three batches of three phials buffered to 5, 7, and 9 pH) and the absorbance and value used to calculate PAI at the initial state using a spectrophotometer (Pye Unicam 8620, Cambridge, UK). Two samples each of bacterial culture were cultured for 5 days under three types of powerline (400kV, 275kV and 132kV) and a third sample of the same placed some 70m, 150m, and 100m distant respectively from the same lines. A similar number of samples were left in the same locations for 10 days, so that the phosphatase activity could be compared between initial state, 5 and 10 days exposure. Each sample was a batch of three (one at 5, one at 7, and one at 9 pH) thus there were in total for the 5 day exposures 18 x 2 = 36 phials of culture exposed to the lines, and 18 distant from the lines ("unexposed"), in addition to the controls. All samples were of handled under a vertical laminar flow unit. Ambient temperature was c. 15 degrees during the exposure period. In order to offer a pathway for the electric component of the powerline fields the phial and flask stoppers were wrapped in aluminium foil before insertion (see photo above). PHOSPHATASE ACTIVITY: RESULTS PAI at the outset (initial state) was calculated from the three pH values of the controls as shown below. Table P1: Phosphatase state at outset of assay
The formula for calculating PAI is DE.V. C. 1000 PAI (pNP/s/dm3) = ----------------- v.t.d where DE is the difference in extraction between trial and control at 420nm, V is the total volume of the reaction mixture, C is the molar extinction coefficient, v is the volume of the sample (in cm3), t is the duration of the enzyme activity, and d is the length of the lightpath in the cuvette (1cm). Phosphatase activity: results after 5 days The results are set out in Table P2 below. Table P2: Phosphatase activity under and distant from HV Powerlines
Phosphatase activity results after 10 days The results after 10 days exposure are shown in Table P3 below Table P3: Phosphatase activity under and distant from HV powerlines
SUMMARY RESULTS The details given in Tables P2 and P3 are shown here for comparison. Table P4: Comparison of phosphatase activity after 5 and 10 days Phosphatase Activity Index after 5 and 10 days under HV electricity lines
These results show an elevation of phosphatase activity under the 400 and 275 kV lines after 5 days, followed by a relative decline after 10 days. Under the 132kV line this elevation appears to be slower to develop. |
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