Heavy metal and organic chemical contaminants in wastewater discharged from leather tanneries in the Lanús district of Buenos Aires, Argentina, April 2011

Labunska, I., Brigden, K., Santillo D. & Johnston, P. (2012) Heavy metal and organic chemical contaminants in wastewater discharged from leather tanneries in the Lanús district of Buenos Aires, Argentina, April 2011. Greenpeace Research Laboratories Technical Note 07‐2011, publ. March 2012: 33 pp.

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Executive Summary

Five wastewater and three sediment samples associated with five leather tanning facilities located in the Lanús district of Buenos Aires (Argentina) were analysed at the Greenpeace Research Laboratories for the presence of heavy metal and organic chemical contaminants, as well as a single sample of water from the main Millán ‘pluvial’ rainwater collection system serving the district.  All samples were collected between 28th April and 5th May 2011 and stored and transported refrigerated and in the dark prior to analysis.  A range of metals and volatile organic chemical contaminants (VOCs) were analysed quantitatively using appropriate standards.  Semi-volatile organic chemicals were analysed qualitatively (to determine their presence only)) through a process of GC-MS screening in SCAN mode.

Key results can be summarized as follows:

  • Concentrations of dissolved chromium in (filtered) wastewaters being discharged by all five tanneries were above what may be expected for uncontaminated surface waters, and furthermore  the concentrations in effluents from the Maria Lettieri and Angel Giordano facilities were particularly high (2330 and 3430 ug/l respectively).  Such high dissolved chromium concentrations, in the absence of detectable levels of chromium (VI), suggest that the less soluble form chromium (III) is being held in solution in the form of soluble complexes with other chemicals in the wastewater.  Despite the apparent absence of chromium (VI) residues in these cases, the toxicity of chromium (III) to the aquatic environment (especially to algae and fish) following release of wastewaters at these levels should not be disregarded, and there is also the potential for oxidative conversion of a proportion of the chromium (III) to chromium (VI) following release.
  • Chromium concentrations were even higher in the whole (unfiltered) water samples, as this includes chromium in suspended matter also.  Concentrations in the five effluents ranged from 208 ug/l to more than 14 000 ug/l (14 mg/l), the highest being recorded in effluent from the Maria Lettieri facility.  Sediments collecting in the effluent discharge pipes which carry wastewater from three of the facilities to the sewer system were found to contain between 3% and 8% chromium by weight, extremely high concentrations possibly resulting in part from the accumulation of insoluble chromium compounds and perhaps small fragments of tanned hide.  Such heavily contaminated sediments may be acting as longer term sources of chromium to the sewer and, thereby, the aquatic environment.
  • Elevated chromium concentrations were even detectable in a single sample of water collected from the Millán ‘pluvial’ rainwater collection system, despite the potential for dilution with run-off and discharges from other sources.  Unfiltered (whole) water from the collector contained 2380 ug/l chromium (i.e. more than 2 mg/l), suggesting a clear signature of chromium inputs arising from the high density of small and medium leather processing enterprises located in the Lanús district.
  • Patterns of contamination of wastewaters and sediments with semi-volatile organic compounds were complex, but showed some characteristics common to many or all of the five facilities sampled.  Between 55 and 83 individual organic compounds were resolved in wastewater samples, and between 94 and 137 in sediment samples, though in both cases the proportion of these which could be reliably identified was relatively low (e.g. only 31-49% total number of compounds in the case of the effluents).  Such a result is common to organic screening analysis of complex wastewaters of this nature, but nonetheless inevitably limits the overall assessment of the nature and extent of chemical contamination.
  • The biocide/preservative chemical 4-chloro-3-methylphenol (p-chlorocresol), known to be used in preventing degradation of hides during processing, was a prominent characteristic in all five tannery effluents and in the water from the ‘pluvial’ collector.  This compound is classified as ‘harmful’ and as ‘very toxic to aquatic life’ under the UN Globally Harmonised System for classification and labeling of chemicals.
  • Among other organic compounds commonly found were other chemicals reportedly used as biocides and leather auxiliaries, including 2-butoxyethanol phosphate, 2-(2-butoxyethoxy)ethanol, quinoline and isoquinoline, hydroxybiphenyl, benzothiazole and 2-methylthiobenzothiazole.  Phthalate esters were also prominent components in some samples, including DEHP, DBP, DiBP and BBP which are all recognised as Substances of Very High Concern under the REACH Regulation within Europe because of their toxicity to reproduction.
  • Effluent from two of the five tanneries (La Teresa and Angel Giordano) also contained residues of the surfactant chemicals nonylphenol ethoxylates, or NPEs (monoethoxylates in this case); that from Angel Giordano also contained the related chemical nonylphenol, also as an isomeric mix.  Nonylphenol (NP) is widely recognised and regulated as a priority pollutant in water, primarily because of its endocrine- (hormone-) disrupting properties in fish and other organisms.  Nonylphenol ethoxylates (NPEs) will also degrade over time to form NP.  The use of these chemicals is therefore prohibited or severely restricted in Europe and in several other parts of the world.
  • Traces of volatile organic compounds (VOCs), in this case chlorinated solvents and by-products of chlorination, were found in all six wastewater samples, though by far the most significantly contaminated was the effluent from the Maria Lettieri tannery.  This sample contained 103 ug/l of cis-1,2-dichloroethene (1,2-dichloroethylene) and 216 ug/l of trichloroethene (trichloroethylene), both of which are classified under the UN GHS as harmful to the aquatic environment.  In addition, trichloroethene is classified as carcinogenic (category 1B) and as a possible genotoxic substance under the UN system.

Further investigations would be necessary in order to try to identify specific process sources of the chemicals identified in the wastewater discharges and associated sediments.  Nonetheless, taken together, the results from this study indicate that the leather tanning and processing industry in Lanús is a significant source of chromium and various organic chemical contaminants to the wastewater receiving system, which ultimately links to, and contaminates, the main ‘pluvial’ rainwater collection system.  Depending on the existence, nature and effectiveness of any subsequent treatment downstream from the point at which the wastewater sample was collected from the Millán ‘pluvial’, such discharges could well also be a significant contributor to wider contamination of surface waters and sediments of the Riachuelo basin.