The blackberries rabbit hole

On Sunday, I went to a small hidden spot to check if the blackberries were ripe for foraging. It’s behind the playing field on Bornitzstraße, and you quickly stumble into dozens of blackberry bushes. No one was around, so I started picking - until a small thought grew bigger: “Is it safe to eat here? This was an industrial area - aren’t the berries polluted?” That question kept nagging at me. There’s some trash here and there (though not right at the front), but is there a better way to find out if it’s safe to eat?

As an ordinary person, it’s not so easy to know. Areas with harmful soil changes or suspected contamination are listed in the soil pollution register (Bodenbelastungskataster, BBK). The data is based on investigations and is regularly updated by the responsible soil protection authority. However, you can’t simply access it without a good reason (and I doubt “picking some blackberries” counts). I’m not even sure if the area is privately owned or public land. So, I could only make an educated guess.

I found a first clue in a map from FIS-Broker (Nährstoffspeicher- / Schadstoffbindungsvermögen der Böden 2015, Umweltatlas)¹. At first, I thought it was a good area with high nutrient storage and pollutant binding capacity, but the blackberry patch is right over an area with low capacity - not a good start.

Looking for more hints, I checked for pollution measurements and found one just a street away, at the Dong Xuan Center. In GDR times, there was the VEB Elektrokohle², and pollutant measurements found plenty of relics from that era:

Elevated levels of polycyclic aromatic hydrocarbons (PAH) in the soil were found all over the place (maximum value 5,086 mg/kg). 7,320 mg/kg phenols were found in the soil of the former phenol basin. MHC, heavy metal and cyanide contamination (area of the former electroplating shop) has been determined selectively; they are concentrated in the approx. 3 m thick filling.³

If that area was highly contaminated, then this one could be too. So I looked at old maps to see what used to be here.

The blackberries are all right under the Reichsmonopolverwaltung. They did Spirits purification and storage⁴. There was also a metallurgy factory right next to it in the 40s^{5 6}.

In GDR times the former Reichsmonopolverwaltung was additionally used as an Oil Storage (Bärensiegel and VEB Pflanzen- und Ölmühle).

It seems likely there’s pollution in the ground. I found a hint from a soil cleaning firm that worked on an old Reichsmonopolverwaltung site. Their investigation found gasoline, diesel, heating oil (MKW), BTEX, CHC/LHKW, cyanide, PAH, perfluorinated surfactants (PFT), phenols/chlorophenols, polychlorinated biphenyls (PCB), and heavy metals in soil and groundwater. More evidence for probable contamination - especially since the old Industriebahn⁷ tracks are still there, just overgrown with blackberries. The tracks themselves could be a source of pollution as well: PAHs and heavy metals are common, with creosote (used for wood preservation) and years of industrial use leaving their mark⁸.

All these points convinced me that foraging blackberries here probably isn’t a good idea. But now I was curious: how do blackberries actually accumulate pollutants? I remembered a study from TU Berlin about urban gardening. I’ll have to reread it, but what stuck with me was that, for example, tomatoes grown on a city balcony can end up contaminated with heavy metals. No other Autobahn in Germany has such bad soil nearby as we do here in the city, where exhaust and pollutants accumulate, and leafy greens are especially good at passing those on to us. The TU study analyzed typical urban gardening plants to see which pollutants they absorb and where they store them - basically, which city-grown edibles to avoid. The bottom line: you don’t want tomatoes, spinach, or herbs from city gardens. Highly watery plants and leafy greens are best avoided if grown in the city. The rule of thumb is that toxins, especially heavy metals, migrate into the wood, so tree fruit is generally safe. Trees are good; an edible balcony on a busy street, not so much⁹.

But what about blackberries? I found some studies that looked into exactly that¹⁰. Turns out, blackberries are very good markers for soil pollution. The leaves, exposed to atmospheric pollutants, are the largest reservoirs of heavy metals (so, never make blackberry leaf tea from city plants!). The berries themselves, sheltered by leaves and ripening slowly, accumulate smaller amounts of heavy metals. Still, even the fruit can pick up pollution just from being in the city, according to the TU study.

So should I just buy blackberries at the supermarket instead? Then I get all the joys of pesticide exposure¹¹. It feels like the only choice is to pick blackberries in a truly remote area with no history of pollution - or just accept the risks.

That simple question—are these blackberries safe to eat?—left me feeling a bit sad, and with even more questions. Is there anywhere left without a pollution source? Why isn’t the Bodenbelastungskataster open data? For now, I’ll just treat blackberry foraging as exercise, not as a snack.