While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Clean Harbors, Inc. (CLH 0.20%) slipped in premarket trading Thursday after Wedbush Securities downgraded the environmental services company from outperform to neutral.

So what: Along with the downgrade, analyst Al Kaschalk lowered his price target to $50 (from $74), representing about 9% worth of upside to yesterday's close. While contrarians might be attracted to yesterday's earnings-related 14% plunge, Kaschalk thinks that Clean Harbors' appreciation prospects remain limited given management's disappointing execution of late.

Now what: According to Wedbush, Clean Harbors' risk to reward trade-off is pretty balanced at this point. "[W]e cannot continue to justify our positive rating until we see an improvement in base business fundamentals and tangible evidence of improved execution on management's part," noted Kaschalk. "Further, management initiated a cost-reduction program to bring cost structure more in line with the company's current revenue profile. We believe a more detailed strategic review of company's business lines could result in small divestitures, while driving an improved capital return profile for the company." Of course, with Clean Harbors now off about 30% from its 52-week highs and trading at a forward P/E in the low teens, Wall Street's concerns might be providing patient Fools with a solid long-term opportunity.