In the directive 2004/107/EC (Fourth Daughter Directive), the EU has set a target value for polycyclic aromatic hydrocarbons (PAH) for the protection of human health; the target is defined in terms of concentration of benzo(a)pyrene (BaP) which is used as a marker substance for PAHs generally: the BaP annual mean value may not exceed 1 nanogram per cubic metre (ng/m3). The target value enters into force 31.12.2012.
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Let the grass grow higher and thus encourage root growth. It will also allow the grass to self-seed. If you mow a path in the middle, it will show that it is indeed meant to be that way as opposed to being neglected.
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