That article is american. US regulations are completely different to uk/EU,
Miracle gro is not any more or less harmfull then Tomorite, Phostrogen, vitax, westland or any other plant food. You say bottle so I assume you have a liquid version rather then the granualted. Thats far less toxic than pouring bleach down the toilet, or urine for that matter. washing up liquid contains salt.
All fertilizers have an NPK ratio.
Nitrogen - promotes leaf growth.
Phosphorous - promotes root growth
Potassium - promotes flower and fruit development
Tomorite will have a higher amount of Potassium
Miracle Gro has a higher amount of Nitrogen and elevated Potassium
Summer lawn food has more nitrogen
Winter lawn food has more Phosphorous
The Article is scaremongering and reads as if they have thier own agenda and I find it strange they singled out 1 particular plant food. The leaching of nitrates from the soil is well known from agricultural use of fertiliser. You would need to be adding buckets of Miracle gro to your garden to come close to causing leaching. In fact people and dog p***ing behind a tree are putting a far more concentrated Nitrogen into the ground than correctly dosed plant food, the majority of which is used in planted pots and baskets anyway. If people do use the hose attachement dispensor they use far too little to have any actual effect on thier plants that water alone would do just as well.
I have 2 14m mixed planted borders. Most people - my neighbour included will wave a hose around for 10minutes a couple of times a week and the water barely wets the surface. They would need to spend several hours everyday filling watering cans to cause the kind of issues mentioned in the article.