Yesterday, I was at the park with my kids after dinner, a “night session” as we call it.

The dandelions, ubiquitous this time of year, had a distinctly sinister curve to their stems that meant they’d been sprayed recently with 2-4-D, the world’s most widely used herbicide. You can smell it vaguely in the air, too, the sweet smell that wafts from outside a nursery. The health effects of 2-4-D are unclear — it’s a synthetic plant hormone — and there’s some concern it can be linked to cancer and Lou Gerhig’s disease. Or, others say, there is no concern.

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Just to be on the safe side, I tell my kids: “Don’t lay on the grass … ” Which, of course, is all they want to do at this hilly park that is ideal for downhill rolling. When the words leave my lips, I can’t believe what I’m saying, in a park, in Colorado, in the spring. But, frankly, there are other reasons not to roll in the grass: dog owners let their pets poop randomly, so a joyous tumble can quickly morph into a public health crisis and complex sanitation project. Or they leave actual bags of poop on the hill, half getting the idea; both the poop and the bags I see as massively inconsiderate and damning of all dog owners. But it seems impossible to resolve.

There is trash in the park too, which we are all reluctant to pick up — why dirty our hands with other people’s waste? — but which I do pick up because I don’t want my children playing in trash.

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The herbicide, the dog poop, the garbage: as a onetime biology major, I guess its back to the future here, the tragedy of the commons all over again, or still. But for me, older than I used to be and less academic about things, this night session in the park is just a reminder that the commons is our children.