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5. Potential Environmental Impacts of Tyre Leachate

The literature reviewed on the environmental impact of tyre leachate is summarised in Sections 5.1 and 5.2. It should be noted, however, the review was not an in-depth analysis of the literature.

5.1 Recent Laboratory Research

Recent laboratory research on tyre leachate reviewed in this study is briefly summarised in Table 5.1.

Table 5.1: Summary of reviewed laboratory research on tyre leachate

Paper

Date

Place

Tyre type

Method

Leachate characteristics

Day

1993

CA

Whole new and used

Inundation in GW sample

Toxic to rainbow trout (not other species). Inhibited some metabolic functions. Unclear if new or used tyres less toxic.

Horner

1996

UK

Chips used

Inundation in simulated acid rain

Zn between 169-463 ppm. Negligible Cd and Pb.

Basher

1996

US

Chips with and without wires

Inundation in distilled water

Cr and Pb not detected, Ba <5 mg/L, Ca between 5-57 mg/L, Zn not measured. Level of organics increased with time.

Azizian

2001

US

Crumb rubber asphalt concrete

Inundation in distilled water

V, Zn, As, Ba, Ni, Co, Fe Cr, Cu, Sb, Pb, Cd and Se not detected. Al, Hg and benzonthiazole levels exceeded levels for aquatic toxicity and increased with time.

Collins

1995

UK

Crumb and retread dust

Inundation in salt water sample

Cd, Cu, Cr, Pb and Ni not detected. Zn levels proportional to amount and inversely proportional to size of tyre. Increase in Zn and organics with time.

Nelson

1993

US

Plugs

Inundation in lake water sample or deionised water

Zn was 0.7 mg/L. Cd, Cu and Pb detected at low levels. Toxic for C.dubia but not minnow.

O'Shaughnessy

2000

CA

Chips

Testing in lysimeter

Al, Fe, Mn > DWL (possibly due to steel), Zn < DWL.

Sengupta

1999

US

Chips

Inundation in distilled water

Substances < PDWS. Substances < SDWS except Fe and Mn.

CIWMB

1996

US

NA

Review

Generally low concentrations of metals leached from tyre piles. Levels of Zn, Mn and Al >SDWS.

CWC

1995

US

Shreds

Review

Water becomes acutely toxic to some fish species if tyres submerged in confined, relatively small amounts of water for several days to weeks.

CIWMB

1998

US

Shreds

Review

Leaching of organics slow, greatest under basic conditions. Metals < PDWS and SDWS except Fe and Mn, greatest leaching under acidic conditions.

Birkholz

2003

CA

Crumb from site

Lab

Toxic to bacteria, invertebrates, fish and green algae tested. 59% reduction in toxicity after crumb onsite for three months.

Gunter

1996

US

Chips, used

Inundated with GW and surface water samples

Fe, Pb, Mn > Wisconsin State Groundwater Quality Standards. Benzene only volatile organic detected.

Texas Department of Transportation

NA

US

Chips

Leaching test of unknown method

Substances < PDWS and SDWS except Mn and Fe. Volatile and semi-volatile organics not detected.

Atech Group

2001

AS

NA

Review

No major environmental impact of tyres in controlled landfills, but limited evidence of long-term impacts.

Notes:

  1. Abbreviations used in table for place names: CA, Canada; UK, United Kingdom; US, United States of America; AS, Australia.
  2. General abbreviations used in table: DWL, Canadian drinking water limits; NA, Not available; PDWS, United States primary (health) drinking water standard; SDWS, United States secondary (aesthetic) drinking water standards.

In the laboratory tyre leachate is often generated by inundating a tyre sample (plug, shred, chip, or crumb) with water. There are limitations when comparing the results of the reviewed laboratory studies as different makes of tyres were used and different compounds were measured; however the following general observations can be made about the tyre leachate generated in the laboratory:

  • it may be toxic to some fish species (eg rainbow trout but not minnow), bacteria, invertebrates and green algae
  • levels of aluminium and manganese are likely to be elevated, especially where steel is exposed
  • levels of mercury and lead may be elevated; however most studies reported negligible levels
  • levels of zinc and organic compounds are likely to be dependent on individual circumstances as a wide range of levels have been reported in the studies reviewed
  • levels of other substances are likely to below United States Drinking Water Standards
  • levels of leachate compounds (metals and organic compounds) are likely to increase with time of inundation, increase proportionally with amount of tyre and decrease proportionally with size of tyre exposed to inundation.

5.2 Recent Field Trials

Recent field trials on tyre leachate reviewed in this study are briefly summarised in Table 5.2.

Table 5.2: Summary of reviewed field trials on tyre leachate

Paper

Date

Place

Method

Leachate Characteristics

Humphrey

1997

US

Tyre chips above GWT in Maine, GW or leachate collected for 2.5 years, control well.

Substances < PDWS. Substances < SDWS except Fe and Mn. Organics not detected.

Horner

1996

UK

Soil samples taken from 10-year-old tyre dump in West London.

Elevated soil Cd, Pb and Zn at base of dump, levels decreased exponentially with distance.

O'Shaughnessy

2000

CA

Tyre reinforced earthfill, leachate collected for two years, no control well.

No significant adverse effects on groundwater. Cd, Cr and Pb not detected. Zn and Fe < regulatory limits.

Humphrey

2001

US

Tyre shreds below GWT in Maine, leachate and downstream GW collected for 2.5 years, control well.

Highest level of contamination seen at site, with contamination decreasing to near background 3 m downstream. Substances < PDWS at site. Substances < SDWS at site except Fe, Mn, Zn and some organics.

Humphrey

2000

US

Tyre chips above GWT in Maine, leachate collected for five years, control well.

Substances with PDWS not altered. Al, Zn, Cl and SO4 not increased at site. Fe and Mn increased at site. Negligible level of organics at site.

Riaz

2001

CA

Shredded tyres in baselayer of road in Manitoba, GW collected, no control well.

Substances < PDWS below site. Substances < SDWS below site except Al, Fe and Mn. Organics not detected.

Notes:

  1. Abbreviations used in table for place names: CA, Canada; UK, United Kingdom; US, United States of America.
  2. General abbreviations used in table: PDWS, United States primary (health) drinking water standard; SDWS, United States secondary (aesthetic) drinking water standards; GWT, groundwater table; GW, groundwater.

In field trials tyre leachate is generated by water percolating through the tyre sample (whole tyre, shred or chip). There are limitations when comparing the results of the reviewed field trials as different makes of tyres were used and different compounds were measured; however the following general observations can be made about the nature of tyre leachate generated in the field:

  • levels of manganese and iron are likely to be elevated in groundwater, especially when steel is exposed
  • levels of aluminium, zinc and organic compounds may be elevated in groundwater; however the majority of studies reported negligible levels
  • level of cadmium and lead may be elevated in soil; however no studies reviewed reported elevated levels in groundwater
  • levels of other substances measured are likely to be below United States Drinking Water Standards
  • level of leachate compounds in groundwater are likely to decrease down gradient of the tyre site.

5.3 General Observations

The potential environmental impacts of tyre leachate are contamination of soil, surface water and groundwater on the site and surrounding area. Based on the reviewed literature and previous MWH experience in site contamination, factors that may affect the rate of leaching and/or the concentration of tyre leachate compounds in soil, surface water and groundwater include:

  • tyre size: leaching from whole tyres is likely to be slower than leaching from tyre chips or shreds - this is because of the differences in the surface area to volume ratio
  • amount of exposed steel: if steel is exposed, say in tyre chips, there is likely to be faster leaching of manganese and iron than from whole tyres where the steel is not exposed
  • chemical environment: leaching of metals is likely to be more rapid under acidic conditions while leaching of organic compounds is likely to be more rapid under basic conditions
  • permeability of soil: leaching is likely to be faster when soils are permeable
  • distance to groundwater table: the greater the vertical distance to the groundwater table, the less likely the contamination of groundwater
  • distance from tyre storage site: the further the downstream distance from the tyre storage site, the lower the contaminant concentration in the soil and groundwater
  • contact time with water: the longer the tyres are in contact with water, the greater the risk of groundwater contamination
  • vertical water flow through soil: the greater the water flow through the soil (eg, from rainfall), the greater the dilution of contaminants
  • horizontal groundwater flow: the greater the groundwater flow, the greater the spread of the contaminant plume
  • leached compounds at site: levels of manganese and iron are likely to be elevated in groundwater when steel is exposed. Levels of aluminium, zinc and organic compounds may be elevated in groundwater. Levels of zinc, cadmium and lead may be elevated in soil.

Specific and general mitigation measures to address the environmental risks associated with tyre leachate are outlined in Section 8.8.