Silver contamination on abiotic and biotic compartments of Nahuel Huapi National Park lakes, Patagonia, Argentina

The Ag contents of abiotic and biotic compartments of different lakes of Nahuel Huapi National Park, Patagonia, Argentina were analyzed. The water bodies studied were lakes Nahuel Huapi, Moreno, Escondido, Espejo Chico and Traful, the latter chosen as a reference lake. The Ag concentration profiles of short sediment cores, dated by (210)Pb and (137)Cs techniques, were analyzed, as well as suspended load collected from three sites of lake Nahuel Huapi. The biota studied were the native mussel Diplodon chilensis (digestive gland and total soft tissues pooled samples) and five species of fish, two native and three introduced (liver and muscle pooled samples). Ag contents were determined by Instrumental Neutron Activation Analysis (INAA). The upper layers of the sediment cores sampled in lake Nahuel Huapi were enriched in Ag contents compared to deep layers in accumulation periods corresponding to the second half of the 20th century, but this enrichment was neither observed in the reference lake Traful, nor in lakes Espejo Chico and Escondido. Ag was enriched over background level (0.1 microg g(-1)) also in suspended load collected in lake Nahuel Huapi. Ag fluxes to sediments were computed for suspended load and enriched sediment core layers. Highest Ag fluxes, from 350 to 470 microg m(-2) year(-1), were measured in Nahuel Huapi near the site where the liquid effluents of the Bariloche city sewage treatment plant are released to the lake. The spatial distribution of the other Ag fluxes suggests that this is the main source of Ag to lake Nahuel Huapi and lateral transport occurs within the water body. Ag concentrations on biota samples were consistent with these conclusions. Mussels collected in lake Nahuel Huapi showed higher Ag concentrations than in the other lakes, especially when compared to lake Traful. Ag contents in mussels were strongly associated with sediment intake, but enriched probably due to sediment grain size sorting during the intake processes. Evidence of food chain biomagnification of Ag in fish liver was observed. Ag contents in fish liver were higher at lake Nahuel Huapi even considering the high intra-specific variability, with highest values ranging from 10 to 29 microg g(-1) dry weight for brown trout and rainbow trout.     

Heavy metals in the vicinity of a chlor-alkali factory in the Upper Negro River ecosystem,Northern Patagonia,Argentina

A study on heavy metal contents was performed in sediments and biota of the Upper Negro River (Alto Valle) aquatic system, Northern Patagonia, Argentina. The irrigation system of the Neuquén and Negro Rivers runs alongside these rivers for 150 km, supporting intensive agricultural and economical activities, mainly related to fruit production. A mercury cell chlor-alkali factory operated between 1951 and 1995. Close attention was given to the surroundings of the plant, located next to the Main Irrigation Channel, and to the PII drainage channel which received the plant's effluents between 1951 and 1979. From 1979 until its closure, the effluents were pumped above a ravine to a series of evaporation and decantation pools. Mercury and other heavy metals and metalloids (Ag, As, Ba, Co, Cr, Cs, Ni, Sb, Se, U and Zn) contents were measured for bottom sediments of the river and irrigation and drainage channels, for two widespread species of macrophytes (Potamogeton pectinatus and Myriophyllum brasiliensi), and for liver and muscle of native fish Odontesthes microlepidotus. River bed sediments show no evidence of heavy metal accumulation, however, biota might indicate that contaminants are entering the rivers. Mercury was the only element accumulated in the Main Irrigation channel sediments, the highest contents occurring in the surroundings of the nowadays shut-down chlor-alkali plant, returning to background values approximately 40 km downstream the plant. At the plant site, sediments from the center of the channel showed a decrease in Hg content in the upper 10 cm layer, ranging from 0.8 to 3.4 microg g(-1), and from 2.8 to 13.7 microg g(-1) in the next 10 cm lower layer. Conversely, the PII drainage channel sediments showed accumulation of Hg (2-4 microg g(-1)), distributed uniformly at different depths and along the channel, until its mouth at Negro river. Mercury contents of macrophytes downstream the chlor-alkali plant are higher than the baseline for the area, and macrophytes and fish liver from the PII drainage channel present the highest content in this element. The drainage channel system showed different degrees of impact, those channels flowing through densely populated areas being the most affected.     

Evaluation of the use of human hair for biomonitoring the deficiency of essential and exposure to toxic elements

Monitoring the nutritional status of essential elements and assessing exposure of individuals to toxic elements is of great importance for human health. Thus, the appropriate selection and measurement of biomarkers of internal dose is of critical importance. Due to their many advantages, hair samples have been widely used to assess human exposure to different contaminants. However, the validity of this biomarker in evaluating the level of trace elements in the human body is debatable. In the present study, we evaluated the relationship between levels of trace elements in hair and whole blood or plasma in a Brazilian population. Hair, blood and plasma were collected from 280 adult volunteers for metal determination. An ICP-MS was used for sample analysis. Manganese, copper, lead and strontium levels in blood varied from 5.1 to 14.7, from 494.8 to 2383.8, from 5.9 to 330.1 and from 11.6 to 87.3 microg/L, respectively. Corresponding levels in hair varied from 0.05 to 6.71, from 0.02 to 37.59, from 0.02 to 30.63 and from 0.9 to 12.6 microg/g. Trace element levels in plasma varied from 0.07 to 8.62, from 118.2 to 1577.7 and from 2.31 to 34.2 microg/L for Mn, Cu and Sr, respectively. There was a weak correlation (r=0.22, p<0.001) between lead levels in hair and blood. Moreover, copper and strontium levels in blood correlate with those levels in plasma (r=0.64 , p<0.001 for Cu) and (r=0.22, p<0.05 for Sr). However, for Cu, Mn and Sr there was no correlation between levels in hair and blood. Our findings suggest that while the idea of measuring trace elements in hair is attractive, hair is not an appropriate biomarker for evaluating Cu, Mn and Sr deficiency or Pb exposure.     

Human placenta as a 'dual' biomarker for monitoring fetal and maternal environment with special reference to potentially toxic trace elements. Part 2: essential minor, trace and other (non-essential) elements in human placenta.

A survey of elemental composition of the human placenta was undertaken to evaluate reference values for minor and trace elements (essential and non-essential). The new data collection was narrowed down to results generated between the period of 1975-2000, since analytical methodology was becoming increasingly reliable with time for many elements. The search revealed the following results (microg/g, based on wet weight): Ca = 770; Cl = 1900; K = 1685; Mg = 100; Na = 360; P = 1700; and S = 350. However, Na, P and S need further confirmation. For a group of essential trace elements following average values were evaluated (microg/g, based on wet weight): Co = 0.007; Cr = 0.03; Cu = 0.9; Fe = 69; I = 0.005; Mn = 0.08; Mo = 0.02; Se = 0.2; and Zn = 10. However, the iodine value needs further confirmation. In addition, information values have been identified for a number of so-called non-essential elements such as Ag, Au, B, Ba, Br, Cs, F, La, Rb, Sb, Sc, Si, Sn, Sr, Ti, V and W. The survey results for toxic trace elements As, Cd, Hg, Ni and Pb are discussed in part 3 of this paper along with placenta as a biomonitor for toxic trace elements.     

Granulometry and the content of toxic and potentially toxic elements in vacuum-cleaner collected, indoor dusts of the city of Warsaw

Twenty-seven sites, together with 23 household dust sample sites, representing the home environment, and four public room dust sample sites, representing working environment (mainly offices) have been described in this paper. The latter were examined to obtain an approximate reference to the home environment data. All the samples were collected between May and July 1997 by a vacuum-cleaner method, in the city of Warsaw, Poland. The granulometry of the dusts was determined by their separation into seven fractions in the range 8-500 microm. The concentrations of Cr, Ni, Cu, Zn, Pb, Br and Fe in the samples were investigated in fractions 8-32, 32-63 and 63-125 microm by the EDXRF technique. The results showed higher concentrations of these elements in finer fractions (8-32 microm). The Pb content in the household dusts was found to be unexpectedly low, ranging from 120 microg g(-1) for the 63-125 microm fraction, up to 210 microg g(-1) for the 8-32 microm fraction. Car exhausts could not be determined clearly as the main source of Pb in the indoor household dusts due to the lack of a Pb-Br intercorrelation. In these dusts, only Cr and Zn showed a remarkably high content of 90-100 and 1020-1070 (microg g(-1)), respectively. In the household dusts, strong intercorrelations were present in the three analysed fractions for the metal pairs: Pb-Zn, Pb-Cu, Fe-Cr, and Cu-Cr (weaker). The working environment rooms showed a higher degree of dustiness by 300%, as compared to the dwellings. The dusts collected in the working environment rooms showed slightly higher concentrations of Ni and by 50-100% higher concentrations of: Cu, Zn, Pb, Br than the analysed household dusts.     

Comparison of green algae Cladophora sp. and Enteromorpha sp. as potential biomonitors of chemical elements in the southern Baltic

The contents of Cd, Cu, Ni, Pb, Zn, Mn, K, Na, Ca and Mg were determined in the green algae Cladophora sp. from coastal and lagoonal waters of the southern Baltic. Factor analysis demonstrated spatial differences between concentration of chemical elements. The algae from the southern Baltic contained more Na and K while the anthropogenic impact of Cu, Pb and Zn was observed in the case of Cladophora sp. and Enteromorpha sp. from the Gulf of Gdansk at the vicinity of Gdynia. This area is exposed to emission of heavy metals from municipal and industrial sources with the main contribution of shipbuilding industry and seaport. The statistical evaluation of data has demonstrated that there exists a correlation between concentrations of Cu, Pb and Zn in both green algae collected at the same time and sampling sites of the Gulf of Gdansk. Our results show that in the case of absence of one species in the investigated area it is still possible to continue successfully the biomonitoring studies with its replacing by second one, i.e. Cladophora sp. by Enteromorpha sp. and vice versa; in consequence reliable results may be obtained.     

Human placenta as a 'dual' biomarker for monitoring fetal and maternal environment with special reference to potentially toxic trace elements. Part 3: toxic trace elements in placenta and placenta as a biomarker for these elements.

The human placenta as a body component is exposed to several harmful substances, depending upon the environmental conditions encountered. In the case of toxic metals, placental tissue can be regarded as a dual biomarker to assess maternal and fetal health. The average range of concentrations for toxic trace elements in placenta based on wet weight are found to be: cadmium 1-6 ng/g; total mercury 2-13 ng/g; methyl mercury 1-14 microg/g; and lead 5-60 ng/g. The placenta appears to be at least a partial barrier for Cadmium. Cadmium transport includes a broad variety of mechanisms. Once in circulation, it mainly interferes with Ca and Zn transportation. On the other hand, placenta appears to be a weaker harrier for Pb than for Cd. In the case of Hg, predominantly the organic form is absorbed and readily crosses the placenta. In fetal blood, the organic mercury content is equal or even greater than in maternal blood, raising questions on normal fetal development. Placenta as a biomarker could be taken as an alternative to repeated maternal blood sampling for assessing lead exposure in utero. Placenta samples are usually obtained at the time of parturition, a one-time event. Hence, each pregnancy has to be looked upon as an RTM (real time monitoring) process since the affected species is exposed to the placental source of pollutants only during the course of that particular pregnancy.     

Levels of aldrin and dieldrin in environmental samples from Delhi, India.

Aldrin and dieldrin residues in soil, earthworms, water, fish and clams from different sites in Delhi were monitored. Concentrations of aldrin and dieldrin were found to be higher in earthworms than in soil. Concentrations of dieldrin were higher in fish than the ambient water, but the concentration of aldrin in the ambient water was the same as that in fish and clams.     

Trace elements in hair: a study of residents in Darjeeling (India) and San Diego, California (U.S.A)

Trace element contents of scalp hair from randomly selected, ethnically homogeneous subjects of Darjeeling (India) were compared with those of the residents of San Diego, California (U.S.A.). The differences between mean concentrations of Ca, Mg, Cu, Na and Cd in the two groups were not significant, and the concentrations of K, Fe, Mn and Zn were significantly higher (P less than 0.01), and that of Al was significantly lower (P less than 0.01), in hair of the residents of Darjeeling. Concentrations of lead in four of the Darjeeling hair samples were very high (greater than 30 micrograms g-1) and in the remaining samples the mean concentration was similar to San diego hair samples. In two mentally retarded Darjeeling subjects, abnormally high values of aluminum (50 and 70 micrograms g-1) and iron (155 and 196 micrograms g-1) were observed. The mean aluminum concentration (2.4 micrograms g-1) in the remaining Darjeeling hair samples was significantly lower than the mean aluminum concentration (10.6 micrograms g-1) in the San Diego hair samples (P less than 0.01). The mean manganese concentration in Darjeeling hair was 20 times higher than the mean manganese content in San Diego hair samples.     

Monitoring Pt and Rh in urban aerosols from Buenos Aires, Argentina

Vehicular traffic is the main source of platinum group elements (PGEs) in highly populated urban areas like Buenos Aires where a traffic density of 1,500,000 vehicles day(-1) (corresponding to 7,500 vehicles km(-2)) is estimated. Since there is no information on the levels of PGEs in Buenos Aires, a pilot study was undertaken to ascertain the amount of two major PGEs, namely Pt and Rh, in the atmosphere of this city. To this end, 49 samples of PM-10 particulate matter were collected during 7 days in seven representative sampling sites located downtown Buenos Aires and spread over an area of about 30 km(2). The collection of particulate matter was performed on ash-free glass-fiber filters using high volume samplers with PM-10 sampling heads. Filters loaded with the particulate matter were subjected to microwave (MW)-assisted acid digestion using a combination of HNO(3), HF and HClO(4). The resulting solutions were evaporated and then diluted with 0.1 mol l(-1) HCl. Analyses were performed by sector field inductively coupled plasma-mass spectrometry (SF-ICP-MS) and special attention was paid to the control of mass interferences. Statistical analysis was performed on the experimental data obtained for the element concentrations taking also into account local meteorological data for the monitored period. The highest concentrations of Pt and Rh were detected at two sites (Hospital Alemán and Casa Rapallini) located in streets with traffic consisting mostly of passenger cars. The Pt content (in pg m(-3)) in airborne particulate matter was found to vary from 2.3 to 47.7, with a mean value of 12.9+/-7, and that of Rh from 0.3 to 16.8, with a mean value of 3.9+/-2.8. These concentrations are by far below the levels for which adverse health effects might be expected to occur, i.e., around 100 ng m(-3). On the other hand, monitoring of PGEs should be carried out in a systematic fashion to detect possible dramatic increases from today's levels.     

Blood lead level and its relationship to certain essential elements in the children aged 0 to 14 years from Beijing, China

Objective

To investigate blood lead level and its relationship to copper, zinc, calcium, magnesium and iron in the children aged 0 to 14 years old from Beijing, China.

Methods

We classified 3181 children into one of the four groups: Group A (n = 783, < 1 year old); Group B (n = 1538, 1-3 years old); Group C (n = 443, 3-7 years old); and, Group D (n = 417, 7-14 years old). All these metal elements were determined by atomic absorption spectrometry.

Results

The blood lead level was 0.207 ± 0.105 μmol/L. There was a significant gender difference for zinc (P < 0.05) in Group C, and there was also a significant gender difference for copper (P < 0.05) and lead (P < 0.05) in Group D. Controlling for gender and age, we observed that there was a negative correlation of lead with zinc (r = − 0.052, P < 0.01), magnesium (r = − 0.042, P < 0.05) and iron (r = − 0.031, P < 0.05), respectively. Furthermore, in the children aged 1-7 years old, we also found there was a negative linear correlation of lead with zinc, magnesium and iron, respectively (P < 0.01).

Conclusion

Blood lead level in children from Beijing was markedly decreased. And deficiency of zinc, magnesium and iron is related to the elevated blood lead level in the children aged 1-7 years.     

Trace elements, PCBs and organochlorine pesticides in New Zealand common dolphins (Delphinus sp.)

Trace elements, polychlorinated biphenyls (PCBs) and organochlorine (OC) pesticide levels were determined in tissues collected from stranded and bycaught common dolphins (Delphinus sp.) from New Zealand waters between 1999 and 2005. The concentrations of mercury (Hg), selenium (Se), chromium (Cr), zinc (Zn), nickel (Ni), cadmium (Cd), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), tin (Sn), lead (Pb), arsenic (As) and silver (Ag) were determined in blubber, liver and kidney tissue. PCBs (45 congeners) and a range of OC pesticides including dieldrin, hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) and its metabolites DDE and DDD were determined in blubber samples. Cr and Ni were not detected in any of the samples and concentrations of Co, Sn and Pb were generally low. Concentrations of Hg ranged from 0.17 to 110 mg/kg wet weight. Organochlorine pesticides dieldrin, HCB, o,p'-DDT and p,p'-DDE were present at the highest concentrations. Sum DDT concentrations in the blubber ranged from 17 to 337 and 654 to 4430 microg/kg wet weight in females and males, respectively. Similarly, Sigma45CB concentrations ranged from 49 to 386 and 268 to 1634 microg/kg wet weight in females and males, respectively. The mean transmission of SigmaDDTs and ICES7CBs between a genetically determined mother-offspring pair was calculated at 46% and 42%, respectively. Concentrations of organochlorine pesticides determined in the present study are within similar range to those reported for Hector's dolphins (Cephalorhyncus hectori) from inshore New Zealand waters.     

Metal accumulation in the green macroalga Ulva fasciata: effects of nitrate, ammonium and phosphate.

Coastal organisms are often exposed to both metal pollution and nutrient enrichment. The influences of major nutrients (nitrate, ammonium, and phosphate) on the accumulation of trace metals (Cd, Cr, Zn and Se) in Ulva fasciata were examined. The relative accumulation of metals was quantified by the kinetic measurements of accumulated metal concentration over a short exposure period (8 h). Our study demonstrated that macronutrients could markedly influence the rate of metal accumulation in the macroalgae. An increase in ambient nitrate concentration resulted in a significant increase in Cd accumulation rate, whereas the rate of accumulation of Cr and Zn was not greatly affected by the ambient nitrate level (between 10 and 100 microM). Zn uptake in nitrate-enriched macroalgae was, however, significantly higher than its uptake in N-starved macroalgae. The accumulation of Cd, Cr and Zn was not appreciably affected by the concentration of ammonium. Se accumulation was significantly inversely related to the ambient phosphate concentration, presumably due to the competitive inhibition by a high P concentration. Cr accumulation in the macroalgae increased significantly with increasing phosphate concentration. These data implied that the influences of major nutrients on cationic and anionic metal accumulation were highly metal-specific. The dependence of metal accumulation on major nutrients will appreciably affect our prediction of metal accumulation in macroalgae and the interpretation of biomonitoring data using the Ulva species.     

Association of toxic and essential metals with atopy markers and ventilatory lung function in women and men

The association of age, smoking, alcohol, superoxide dismutase (SOD), glutathione peroxidase (GPx), blood lead (BPb) and cadmium (BCd) levels, and serum levels of copper (SCu), zinc (SZn) and selenium (SSe) with atopic status and ventilatory function was examined in the groups of 166 women and 50 men with no occupational exposure to metals or other xenobiotics. Markers of atopy included serum total IgE, skin prick test (SPT) to common inhalatory allergens, non-specific nasal reactivity (NNR) and non-specific bronchial reactivity (NBR). Parameters of ventilatory function included forced vital capacity (FVC) and forced expiratory volume in the first second (FEV(1)). Significantly higher BPb, SZn, IgE and prevalence of positive SPT, and lower SCu and NNR was found in men than in women. Fifteen women taking female sex hormones (HT) had significantly higher SCu than women without HT. Regression models showed significant inverse associations between IgE and SCu (P=0.021) and NNR and SCu (P=0.044) in women. When excluding women with HT, the association of SCu and total IgE became of borderline significance (P=0.051), association between SCu and NNR disappeared, and significant positive association between total IgE and BPb emerged (P=0.046). In men, significant inverse association was found between positive SPT and SSe, and between NBR and SSe. A decrease in FVC% and FEV(1)% was associated with an increase in smoking intensity (P<0.001) and a decrease in SZn (P=0.043 and P=0.053, respectively). These results were observed at the levels of the metals comparable to those in general populations worldwide. The observed differences between men and women may partly be explained by different levels of relevant toxic and essential metals, and their combination. The role of female HT in associations of atopy markers and SCu should be further investigated.     

Concentrations of four essential trace elements in breast milk of mothers from two socio-economic groups: preliminary observations

Concentrations are reported for Cu, Mn, Mo and Zn in human milk samples obtained from mothers belonging to low and middle per capita family income groups. The trace element levels in milk of both groups are compared for samples obtained at two stages, viz. 3-5 days and 4-6 weeks post partum. Although the Mn level during the first stage appears to be lower in samples from the low income group, the difference is not statistically significantly (p less than or equal to 0.01). However, at 4-6 weeks post partum, Zn is significantly lower (p less than or equal to 0.01) in milk of mothers belonging to this group.     

Suitability of urban wastes for crop production in Zaria,northern Nigeria: bioavailability and geochemical fractions of potentially toxic elements

A savannah soil amended with two urban wastes and planted with sorghum (Sorghum bicolor) in a pot experiment was evaluated for chemical forms and phytoavailability of Cr, Ni and Pb. The metals were partitioned into seven operationally defined chemical fractions: mobile (F1), easily mobilisable (F2), occluded in Mn oxides (F3), organically bound (F4), occluded in amorphous Fe oxides (FeOx_am, F5), occluded in crystalline Fe oxides (FeOx_c, F6), and residual (F7). Although the application of the urban wastes increased the total concentrations of the metals in the soil, there were no corresponding increases in Cr and Ni uptake by sorghum except for Pb uptake. Waste application increased mobile Ni (F1) but decreased the residual form (F7). The organically bound Pb (F4) was increased at the expense of residual Pb (F7). With respect to Cr, waste application increased Cr form occluded in non-crystalline Fe oxides (F5) in the soil. Bioassay of the test crop indicated that the uptake of Pb by sorghum (Y-Pb) correlated significantly with Pb occluded in non-crystalline and crystalline Fe oxides (F5 and F6). Since a single application of urban wastes to this savannah soil significantly increased Pb uptake by sorghum, the consequences of long-term applications under urban and peri-urban agriculture (UPA) should be of great concern; particularly with respect to children’s exposure to Pb through consumption of food and vegetables.     

Concentration of some toxic elements in Oryctolagus cuniculus and in its intestinal cestode Mosgovoyia ctenoides, in Dunas de Mira (Portugal)

The need for sentinel organisms reflecting small-scale changes in heavy metal pollution of different habitats has been previously stated and the role of terrestrial mammalian parasites has been pointed out as an important field of research aiming at the potential use of parasitic models as bioindicators. The scope of the present study was to assess the concentration of some toxic (Cd, Pb, As and Hg) elements in Dunas de Mira (Natura 2000 PTCON055) while testing the model constituted by the wild rabbit (Oryctolagus cuniculus Linnaeus, 1758) and its intestinal cestode parasite Mosgovoyia ctenoides Railliet, 1890 as potential bioindicators. Wild rabbits were harvested by hunters and analysed for intestinal cestodes. Samples of kidney, liver, intestinal mucosa, muscle of host and also M. ctenoides were taken and deep-frozen for posterior element analysis by ICP-MS. In general, levels of contamination in rabbit tissues were found to be low although some of the elements were detected in higher quantities when compared to other previous reports for wildlife in Europe. The highest quantity of Pb was found in rabbit muscle (3.81 ppm) while highest Cd and Hg values were found in kidney (1.02 and 0.08 ppm). Significant linear relationships were found between Pb concentration in the parasite and Pb concentration in kidney (P=0.0047), muscle (P=0.0002) and intestinal mucosa (P=0.0181) and between As concentration in the parasite and As concentration in liver (P=0.0024), kidney (P=0.0010), muscle (P=0.0003) and intestinal mucosa (P=0.0047). The most significant relationships for Pb and As were detected between element concentration in the cestode and in host muscle. However, maximum Pb and As concentrations in M. ctenoides were only twice as high as those found for rabbit kidney and therefore it is not possible to confirm the role of the model O. cuniculus/M. ctenoides as a promising bioindicator system unlike other mammalian host/cestode models tested in other studies. The contrasting results might be due to differences in the absorption processes in the tegument of different cestode families. Furthermore, the large size of the cestodes used in the present study might also explain the relatively low element concentration values obtained.     

Speciation and ecological risk of toxic elements in estuarine sediments affected by multiple anthropogenic contributions (Guadiana saltmarshes, SW Iberian Peninsula): I. Surficial sediments

Recent studies have demonstrated that the Guadiana Estuary contains metal concentrations in excess of background values. Therefore, this work aims to document the potential environmental hazards associated with the availability of these metals in this environment of high ecological value. Mineralogical analysis shows that the sediments are composed mainly of quartz, albite, and clay minerals (illite, smectite, kaolinite, and vermiculite) along with several small, reactive compounds (including soluble sulphated salts, Fe-Mn oxyhydroxides, organic matter, and pyrite) capable of retaining metals, which can be subsequently released, causing environmental degradation. BCR sequential extraction shows that As, Cd, Cu, Mn, Pb, and Zn present mobile fractions with respect to the total metal content (41, 100, 57, 53, 70, and 69%, respectively) in any of the described reactive phases (F1 + F2 + F3).Calculated environmental risk indices demonstrate moderate to considerable ecological risk for almost the entire estuary, associated mainly with acid mine drainage from the nearby Iberian Pyrite Belt. In addition, the indices highlight several zones of extremely high risk, which are related to industrial and urban dumps in the vicinity of the estuary and to heavy traffic on the international bridge.     

The occurrence and removal of nitrogen in subsurface agricultural drainage from the San Joaquin Valley, California

During the years 1967–1973 there have been extensive studies of subsurface agricultural drainage in the San Joaquin Valley of California. These studies, by cooperating state and federal agencies, were to determine the composition and quantity of drainage waters produced from irrigated agriculture, to evaluate possible methods of removing problem constituents (mainly nitrogen) from these waters, and to obtain an idea of the effectiveness of the treatment methods studied for reducing the waters biostimulatory content with respect to potential receiving waters. The results of the studies indicated that on an annual average, the drainage waters will probably contain about 20 mg NO₃-N I⁻¹ even after 50 years of leaching and that most of the nitrogen is derived from native soil nitrogen. Treatment studies demonstrated that the nitrogen could be reduced from 20 to 3–5 mg N I⁻¹ by any one of several biological treatment processes including bacterial denitrification (filter and pond), algae growth and harvesting, and by a combination plant growth—bacterial denitrification (“symbiotic”) process. Cost estimates for the processes studied ranged from $10 to $36 1000⁻¹ m³ (1969 dollars). Laboratory algal assays demonstrated that the nitrogen removal systems studied effectively reduced the drainage waters biostimulatory content.