Tired tyres sup­ply beat­ing de­mand

Matamata Chronicle - - Rural Delivery - By BALA TIKKESETTY

IT’S un­clear how many old tyres are dis­carded an­nu­ally in the Waikato but it’s es­ti­mated about four mil­lion a year are worn out na­tion­ally, gen­er­at­ing about 36,000 tonnes of waste.

So it’s a fair bet to say the Waikato to­tal is in the hun­dreds of thou­sands. Re­cy­cling ini­tia­tives can’t keep pace with the vol­umes of old tyres gen­er­ated so most end up in land­fills.

Old tyres can some­times be put to good use on farms but it pays to be care­ful in the way they’re used as they can cause en­vi­ron­men­tal dam­age.

Us­ing them on silage stacks is a good use that has lit­tle po­ten­tial to harm the en­vi­ron­ment.

But, some farm­ers are us­ing old tyres as part of farm drainage sys­tems where the tyres can cause grad­ual and in­sid­i­ous pol­lu­tion of wa­ter. This pol­lu­tion is largely un­seen and of­ten not ob­vi­ous vis­ually.

When a tyre comes into con­tact with wa­ter some of the con­stituents in the tyre can leach into the sur­round­ing en­vi­ron­ment.

Tyres con­tain nat­u­ral and syn­thetic rub­bers, car­bon black, oils and resins, sul­phur, tex­tiles, steel and as­sorted chem­i­cals that have been left over from the man­u­fac­tur­ing process.

Chem­i­cals used to man­u­fac­ture tyres in­clude sol­vents, agents used to ac­ti­vate, ac­cel­er­ate, slow or ter­mi­nate rub­ber vul­can­i­sa­tion, cur­ing agents, ad­he­sives and an­tiox­i­dants.

Two key classes of con­tam­i­nants in tyre rub­ber are zinc and poly­cyclic aro­matic hy­dro­car­bons.

Or­di­nar­ily, with only one or a small num­ber of tyres, the size of this leach­ing ef­fect is quite small and may not be no­tice­able. But in cases where a rea­son­ably large num­ber of tyres are brought to­gether or wa­ter is al­lowed to pool in­side a tyre over an ex­tended pe­riod, the strength and tox­i­c­ity of tyre rub­ber leachate can be­come quite sig­nif­i­cant.

Re­search on the en­vi­ron­men­tal im­pacts of tyre leachate re­veals that:

Con­cen­trated tyre leachate is toxic to some fish species, in­sect life and mi­cro­bial or­gan­isms.

Most of this tox­i­c­ity is thought to be associated with the leached zinc. Con­cen­tra­tions of zinc in tyre rub­ber are about 10,000 to 15,000 mg/kg (parts per mil­lion).

Tyre leachate can con­tain high lev­els of sev­eral other met­als and a range of man­made or­ganic sub­stances. Of these, com­pounds called ‘‘ben­zoth­ia­zoles’’ are re­garded as be­ing di­ag­nos­tic of the pres­ence of tyre rub­ber in the en­vi­ron­ment.

Some con­tam­i­nants that leach from tyres do not de­grade but in­stead tend to build up in the sur­round­ing soil or nearby sed­i­ment.

Phys­i­cally, tyres are also not de­signed to serve as sec­tions of drainage pipe. In some cases, poorly de­signed drainage struc­tures us­ing tyres can dam­age the habi­tat of aquatic or­gan­isms and im­pede or block the pas­sage of na­tive and other fish species.

For these var­i­ous rea­sons, En­vi­ron­ment Waikato does not al­low the use of tyres in farm drainage ap­pli­ca­tions.

Sim­i­larly, stock­pil­ing of tyres greater than the num­ber needed for silage stacks is not al­lowed as it can cause the sorts of leach­ing prob­lems out­lined above and also be a fire risk Leach­ing oc­curs when rain­wa­ter runs over and through the stock­pile.

Some of the leached chem­i­cals can en­ter wa­ter­ways and oth­ers can grad­u­ally build up in the soil.

Over the longer term, this grad­ual build-up of con­tam­i­nants in soil un­der and near large tyre stock­piles has the po­ten­tial to cre­ate a con­tam­i­nated site.

Burn­ing tyres also burn to pro­duce a thick toxic smoke. To pro­tect hu­man health, the Na­tional En­vi­ron­men­tal Stan­dard for air qual­ity pro­hibits burn­ing of tyres in the open area.

Tyre stock­piles can also be breed­ing grounds for pests, such as rats and mos­qui­toes.

Tread: Care­fully with tired tyres.

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