USE OF THE FRESH WATER PLANTS ZANNICHELLIA PALUSTRIS AND MYRIOPHYLLUM ACUATIUM FOR BIOMONITORING OF Cd,Pb, AND Cu IN ANDEN RIVERS OF CHILE
Equipment and procedures
Freeze-drying: For freeze-drying a Finn-Aqua, Hürth, Germany LYOVAC GT2 was used together with a Leybold trivac D8B vacuum pump. The freeze drying was performed at 22ºC to the final pressure of 6,2x10-2 mbar.
Homogenization: Homogenization was performed with a Fritsch, Idar-Oberstein, Germany, Planetary Mill Pulverisette 5 made of ZrO2 at 225 rpm for 60 min.
Digestion: Water samples were digested by UV (Kuerner, Rosenheim, Germany)
Residual water determination: The dry mass-correction with infrared was accomplished by a Mettler Toledo, Germany, LP16-M infrared balance. Sub-samples used for the determination of the correction factor cannot be used for elemental determination due to loss of volatile elements15).
Determination: DPASV curves for the simultaneous determination of cooper, cadmium and lead were recorded after a digestion procedure with the model 348B Polarographic Analyzer using the 303A Static Mercury Drop Electrode both from EG&G PAR (Princeton, NJ). Details of determination procedure are presented in Table II. Using the method of calibration curve at low concentration level 16) following detection limits for used parameter and recalculated to the dry mass were found: for cadmium 5 ng/g, for lead 5 ng/g and for copper 50 ng/g.
Table II. Experimental conditions for Cd, Pb, and Cu determination by Differential Pulse Anodic Stripping voltametry (DPASV)
* Supporting electrolyte: 10 ml de HCIO4 s.p. ( 79 % Merck) diluted to 10g with deionized water (Milli-Q-Water-Purification-System, Millipore, Germany).
Reagents and reference solutions
Deionized water was obtained from a Milli-Q-Water-Purification-System (Millipore, Germany). All reagents were Merck (Darmstadt, Germany). Acids used in the wet digestion procedures was HClO4 (70% s.p.) and HCl (30% s.p.) and HNO3 (65% p.a.) distilled under sub-boiling conditions prior to use. Stock standard solutions (1g/L) of Cu2+, Cd2+ and Pb2+ were prepared from Tritisol solutions and acidified at pH <2.
Sea Lettuce BCR-CRM 279 was employed as certified reference material for optimizing and setting up the analytical procedure.
Digestion procedure
About 0.200±0.001g of the dry sample was weighed into 50-ml quartz vessels (suprasil). 2 ml of a mixture of acids, HNO3/HCl04, at a ratio of 40:1 was added. The vessels were covered with quartz lids and put on a electric heater at 50ºC for 15 minutes. They were placed at room temperature until the originally foamy and dark solution became light yellow. Later, heat was applied and temperature was gradually increased up to 330ºC. The vessels were permanently covered so that, with a near reflux, acid evaporation could be slowed down and thus obtain a better mineralization of the sample17,18). The acids were evaporated and after cooling pure water and 0.1 ml of HClO4 was added. If the final residue is dark or colored, a new portion of the acid mixture must be added and mineralization be repeated. The silicon content must be quantitatively collected. It is important to note that the mineralized samples had a high SiO2 content.
The resulting solution was quantitatively transfered into an 10 ml polyethylene flask and diluted with water to the end volume of 10 ml. The solution was stored in refrigator at 4ºC until the analytical stage.
Quality Control
The analytical procedure was tested using the certified reference material Sea Lettuce BCR-CRM-279. The results obtained for all the metals are in an excellent agreement with the certified values for the method of open wet digestion (Fig. 4).
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Fig. 4 Concentration of Cd (mg/g) by DPASV after open wet digestion in quartz vesseles in Sea Letuce samples (BCR-CRM 279) with differet weights. |
For external quality control, some of samples were analysed by the German Environmental Specimen Bank at the Institute of Applied Physical Chemistry, Research Center of Jülich, Germany using ICP-MS. Table III present the comparison between the data obtained by ICP-MS and DPASV. No significant differences between both methods were observed.
Table III. Interlaboratory comparison of Cd, pb, and Cu determination in some fresh water plants.
RESULTS AND DISCUSION
From Table IV it is obvious that the Rio Loa in the water composition deviate from "normal" river water. Concentrations of alkaline and earth alkaline elements in river water from North Chile are significantly higher than those found in "normal" river waters, but below the concentration present in sea water.
Table IV. Water composition of Río Loa in comparison with other rivers
The water content of the plants was measured as the difference between fresh mass and mass after freeze-drying. Water content was generally 71% for both types of plants. Due to handling in the laboratory environment, after freeze-drying some residual water was present in the samples. The mass correction factor for dry weight was estimated by balance with an infrared oven at 105ºC. In all the samples the residual water content was about 4%.
Element pattern of Zannichellia palustris (Fig. 5a) and Myriophyllum acuatium (Fig. 5b) indicate that manganese concentration in both kind of water plants probably due an biological regulation mechanism is very similar and not depend on sampling area.
As, Cu, Pb, Se, Sr, Tl and Ba concentrations are similar in both types of plants (Fig. 5a and 5b), but depend strongly on sampling area. Very high As concentrations found in all sampling areas confirm the high pollution level of natural waters with arsenic in North Chile19,20). Very high Tl concentrations found in two sampling areas indicate some point sources of this element exist, where nature will be identified in the future.
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Fig. 5a. Element pattern of Zannichellia palustris |
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Fig. 5 b. Element pattern of Myriophyllum acuaticum |
Co, Ni, Zn and Cd concentrations found in Myriophyllum acuatium were significant higher than in Zannichellia palustris.
The results obtained by DPASV show, that the species studied have wide tolerance ranges for cadmium and copper (Table V). Observed range for cadmium is from 0.72 to 32 µg/g. These very high concentrations were not found in sea water algae 21). It seems that the tributary stream Rio Salado is highly polluted by cadmium. In a sampling area close to the sources (AT-M) the highest cadmium, lead and copper concentration was found in Myriophyllum acuatium. It is probable that the pollution is related to the volcano activity, which shows up in the geyser at the Tatio. Down stream (sampling area S-M) lower concentrations of cadmium, lead and copper were observed and there is the obvious dilution of elements with increasing distance from the sources. In the river Loa the situation is more complicated. In samples from sampling area Q-M cadmium values of about 10 µg/g were found. Up-stream (sampling area LEQ-M) less cadmium content was found. Down-stream (sampling area CL-M) the lowest cadmium concentration was found. These localized source of cadmium pollution is due human activities. There are important anthropogenic sources of heavy metals in the sampling areas: a sewerage discharge point at La Cascada (sampling area CAS-Z), west of Calama, and the use of fertilizers in agricultural areas (Quinchamale, Chiu-Chiu, Lasana, Ayquina, etc.). Besides, water rights management in the upper portion of the Loa basin influences directly the composition of its lower waters.
Table V. Element concentrations (d.w.) in fresh water plants
Lead concentrations found in both fresh water plants were comparable with concentrations observed also in other algae22). In the river Loa only in one sampling area (CL-M), an increased lead level was observed. At this sampling area also a high copper concentration was found. Probably the pollution by both elements is based on mining activities.
In the upper part of the Loa, the waters have a high copper concentration from the origin itself. According to the geological profile23), the Loa originates near to the Miño volcano, a sector where there is an outcrop of a non-exploited copper porphide rock. This influences directly the composition of water since this constantly leach the rocks in the deposit. Elevated copper concentrations were found in samples collected up-stream, which is in agree with the geological situation. In samples collected down-stream, less copper was found. In some sampling areas close to the mine Chuquicamata (CL-M, SL-M, SL-Z and CAS-Z), the influence of mining activity to the copper concentration in water can not be excluded.
CONCLUSIONS
Low concentrations of Cd, Pb and Cu in fresh water samples make the use of these matrix for monitor of heavy metals difficult, because the detection limits of that technique is in many cases very close to the determined concentrations. Also errors by sampling and processing before determination can falsify the results.
This preliminary study demonstrates that fresh water plants Zannichellia palustris and Myriophyllum acuatium bioaccumulate these elements at concentration levels which are easy to analyse by common analitical method with less probability on analytical errors.
In future work it is necessary to estimate the biological variabilty between individual plants at one sampling area and estimate the bioaccumulation factors for both plants based on adequate water analysis.
ACKNOWLEDEMENTS
Financial suport of the Universidad Católica del Norte, Chile, and of the International Bureau of Research Center Jülich, Germany, are greatfully acknowledged.
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